Patent Publication Number: US-2011059275-A1

Title: Insulated glazing units

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 11/381,733, filed May 4, 2006, published on Aug. 24, 2006, as U.S. Publication No. 2006-0187608, now U.S. Pat. No. 7,832,177, issued on Nov. 16, 2010. Application Ser. No. 11/381,733 is a Continuation-In-Part of U.S. patent application Ser. No. 10/766,493, filed Jan. 27, 2004, published on Sep. 30, 2004, as U.S. Publication No. 2004-0188124, now abandoned. Application Ser. No. 11/381,733 also claims benefit of U.S. Provisional Application Nos. 60/707,367, filed Aug. 11, 2005 and 60/678,570, filed May 6, 2005. Application Ser. No. 10/766,493 is a Continuation-In-Part of U.S. patent application Ser. No. 10/713,475, filed Nov. 14, 2003, published on Jun. 3, 2004, as U.S. Publication No. 2004-0104460, now U.S. Pat. No. 6,962,834, issued on Nov. 8, 2005. Application Ser. No. 10/766,493 also claims benefit of U.S. Provisional Application Nos. 60/531,882, filed Dec. 22, 2003; 60/454,922, filed Mar. 13, 2003; 60/442,922, filed Jan. 27, 2003; and 60/442,941, filed Jan. 27, 2003. Application Ser. No. 10/713,475 is a Continuation-In-Part of U.S. patent application Ser. No. 10/133,049, filed Apr. 26, 2002, published on Oct. 9, 2003, as U.S. Publication No. 2003-0188881, now U.S. Pat. No. 6,723,379, issued on Apr. 20, 2004. Application Ser. No. 10/713,475 also claims benefit of U.S. Provisional Application Nos. 60/442,922, filed Jan. 27, 2003; 60/442,941, filed Jan. 27, 2003; and 60/426,522, filed Nov. 15, 2002. Application Ser. No. 10/133,049 is a Continuation-In-Part of U.S. patent application Ser. No. 10/104,315, filed Mar. 22, 2002, now U.S. Pat. No. 6,627,814, issued on Sep. 30, 2003. 
     U.S. Pat. Nos. 7,832,177; 6,962,834; 6,723,379; 6,627,814; and Patent Application Publication Nos. 2006-0187608; 2004-0188124; 2004-0104460; 2003-0188881 are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The current invention relates to thermally insulated building windows, and more particularly to multi-pane glazing units having a vacuum or a thermally insulating material disposed in the space between the windowpanes. 
     BACKGROUND OF THE INVENTION 
     Photonic, photovoltaic, optical and micro-mechanical devices are typically packaged such that the active elements (i.e., the emitters, receivers, micro-mirrors, etc.) are disposed within a sealed chamber to protect them from handling and other environmental hazards. In many cases, it is preferred that the chamber be hermetically sealed to prevent the influx, egress or exchange of gasses between the chamber and the environment. Of course, a window must be provided to allow light or other electromagnetic energy of the desired wavelength to enter and/or leave the package. In some cases, the window will be visibly transparent, e.g., if visible light is involved, but in other cases the window may be visibly opaque while still being “optically” transparent to electromagnetic energy of the desired wavelengths. In many cases, the window is given certain optical properties to enhance the performance of the device. For example, a glass window may be ground and polished to achieve certain curve or flatness specifications in order to disperse in a particular pattern and/or avoid distorting the light passing therethrough. In other cases, anti-reflective or anti-refractive coatings may be applied to the window to improve light transmission therethrough. 
     Hermetically sealed micro-device packages with windows have heretofore typically been produced using cover assemblies with metal frames and glass window panes. To achieve the required hermetic seal, the glass window pane (or other transparent window material) has heretofore been fused to its metallic frame by one of several methods. A first of these methods is heating it in a furnace at a temperature exceeding the window&#39;s glass transition temperature, T G  and/or the window&#39;s softening temperature T S  (typically at or above 900° C.). However, because the fusing temperature is above T G  or T S , the original surface finish of the glass pane is typically ruined, making it necessary to finish or re-finish (e.g., grinding and polishing) both surfaces of the window pane after fusing in order to obtain the necessary optical characteristics. This polishing of the window panes requires additional process steps during manufacture of the cover assemblies, which steps tend to be relatively time and labor intensive, thus adding significantly to the cost of the cover assembly, and hence to the cost of the overall package. In addition, the need to polish both sides of the glass after fusing requires the glass to project both above and below the attached frame. This restricts the design options for the cover assembly with respect to glass thickness, dimensions, etc., which can also result in increased material costs. 
     A second method to hermetically attach a transparent window to a frame is to solder the two items together using a separate preform made of a metal or metal-alloy solder material. The solder preform is placed between a pre-metallized window and a metal or metallized frame, and the soldering is performed in a furnace. During soldering, no significant pressure is applied, i.e., the parts are held together with only enough force to keep them in place. For this type of soldering, the most common solder preform material is eutectic gold-tin. 
     Eutectic gold-tin solder melts and solidifies at 280 degrees Celsius. Its CTE at 20 degree is 16 ppm/° C. These two characteristics cause three drawbacks to the reliability of the assembled window. First, the CTE of Mil-Spec kovar from 280° C. to ambient is approximately 5.15+/−0.2 ppm/0 C, while most window glasses intended for sealing to kovar have higher average CTEs over the same temperature range. During cooling from the set point of 280° down to ambient, the glass is shrinking at a greater rate than the kovar frame it&#39;s attached to. The cooled glass will be in tension, which is why it is prone to cracking. To avoid cracking, the glass should have an identical or slightly lower average CTE than the kovar so as to be stress neutral or in slight compression after cooling. Using solders with lower liquidus/solidus temperatures puts the kovar at a higher average CTE, more closely matching the average CTE of the glass. However, this worsens the second drawback of metal-allow solder seals. 
     The second drawback to soldering the glass to the kovar frame is that the window assembly will delaminate at temperatures above the liquidus temperature of the employed solder. Using lower liquidus/solidus temperature solders, while reducing the CTE mismatch between the kovar and glass, further limits the applications for the window assembly. Most lead-free solders have higher liquidus/solidus temperatures than the 183° C. of eutectic Sn/Pb. Surface-Mount Technology (SMT) reflow ovens are profiled to heat Printed-Wiring Board (PWB) assemblies 15-20 degrees above the solder&#39;s liquidus/solidus temperature. So the SMT reflow-soldering attachment to a PWB of a MOEMS device whose window was manufactured using lower melting-point solder preforms might have the unfortunate effect of reflowing the window assembly&#39;s solder, causing window delamination. 
     The third drawback is that the solder, which is the intermediate layer between the glass and the kovar frame, has a CTE up to three times greater than the two materials it&#39;s joining. An intermediate joining material would ideally have a compensating CTE in-between the two materials it&#39;s bonding. 
     A third method to hermetically attach a glass window to a frame is to solder the two items together using a solder-glass material. Solder-glasses are special glasses with a particularly low softening point. They are used to join glass to other glasses, ceramics, or metals without thermally damaging the materials to be joined. Soldering is carried out in the viscosity range h where h is the range from 10 4  to 10 6  dPa s (poise) for the solder-glass; this corresponds generally to a temperature range T (for the glass solder or solder-glass) within the range from 350° C. to 700° C. 
     Once a cover assembly with a hermetically sealed window is prepared, it is typically seam welded to the device base (i.e., substrate) in order to produce the finished hermetically sealed package. Seam welding uses a precisely applied AC current to produce localized temperatures of about 1,100° C. at the frame/base junction, thereby welding the metallic cover assembly to the package base and forming a hermetic seal. To prevent distortion of the glass windowpane or package, the metal frame of the cover assembly should be fabricated from metal or metal alloy having a CTE (i.e., coefficient of thermal expansion) that is similar to that of the transparent window material and to the CTE of the package base. 
     While the methods described above have heretofore produced useable window assemblies for hermetically sealed micro-device packages, the relatively high cost of these window assemblies is a significant obstacle to their widespread application. A need therefore exists, for package and component designs and assembly methods, which reduce the labor costs associated with producing each package. 
     A need still further exists for package and component designs and assembly methods that will minimize the manufacturing cycle time required to produce a completed package. 
     A need still further exists for package and component designs and assembly methods that reduce the number of process steps required for the production of each package. It will be appreciated that reducing the number of process steps will reduce the overhead/floor space required in the production facility, the amount of capital equipment necessary for manufacturing, and handling costs associated with transferring the work pieces between various steps in the process. A reduction in the cost of labor may also result. Such reductions would, of course, further reduce the cost of producing these hermetic packages. 
     A need still further exists for package and component designs and assembly methods that will reduce the overall materials costs associated with each package, either by reducing the initial material cost, by reducing the amount of wastage or loss during production, or both. 
     Many types of multi-pane insulated window assemblies are known. A conventional multi-pane insulated window assembly consists, at a minimum, of two windowpanes joined by a frame that maintains a space between them. The space is filled with air or another thermally insulating material, typically a gas. Multi-pane insulated window assemblies typically have better thermal insulation properties than single-pane windows; however, further improvement in insulating performance is often desired. 
     A vacuum-glazing unit (VGU) is a window assembly similar to a multi-pane insulated window assembly, except a vacuum or partial vacuum is maintained in the space between the windowpanes. The purpose of this type of construction is to produce an insulated window unit with a higher level of thermal insulation that can be obtained from air- or gas-filled insulated window assemblies. To date, however, many problems have been experienced in producing durable and reliable VGUs. For example, it has proven difficult to achieve seals between the windowpanes and the frame having the hermeticity necessary to maintain a vacuum (or partial vacuum) for an extended period. Further, it has proven difficult to produce VGUs for exterior wall installations (i.e., for use in the outside-facing (exterior) walls and doors of buildings) that can withstand large and/or rapid thermal cycling (e.g., caused by changes in outside temperatures and/or use of high-performance HVAC systems) without eventually leaking or cracking. A need therefore exists, for improved VGUs and methods of producing durable and reliable VGUs suitable for use in exterior walls and doors, as well as for other applications. 
     A Jun. 10, 2005 Department of Energy (DOE) solicitation states that the key technical challenges associated with highly insulating fenestration products include, but are not limited to: larger size (˜25 sq. ft. and larger), improved durability, excessive weight, seal durability, and high cost. Without an aggressive program to change the energy-related role of windows in buildings, it will thus be virtually impossible to meet Zero Energy Buildings goals. The DOE&#39;s Window Technology Industry Roadmap (Roadmap), published by the Office of Building Technology, State and Community Programs (BTS), after listing several areas of window technology in need of improvements, states such improvements have not been realized due to factors including: High-first-cost of improved products; the cost and questionable durability of existing highly-insulating window technologies; the lack of industry collaboration to improve insulation technology and manufacturing methods; and the presumed high-risk-low-return ratio of investments in improved technologies. 
     In fact, the window industry has not improved the basic technology or reliability of insulating windows for decades. Manufacturers use an adhesive to bond pairs of windowpanes to an intermediate spacer to achieve an airtight cavity between the windowpanes. No epoxy, glue or other adhesive in use today is airtight. All permit some amount of gas exchange to occur. According to data published in 2002 by The Sealed Insulated Glass Manufacturers Association (SIGMA), warranty claims for installed insulated glass (IG) window units due to seal failures is 4% ten years after installation, and almost 10% fifteen years after installation. Most window units do not identify the manufacturer. Many homeowners consciously or inadvertently choose to live with the failed window seals and water condensation between the IG windowpanes that reduce energy efficiency. The majority of IG unit (IGU) seal failures are not considered in the SIGMA data. The actual number of IGU seal failures 15 years after installation is unknown and believed to be very high. All of these conditions are bleeding us of energy. 
     Some academic institutions, companies and government labs have tried achieving higher insulating values (higher R-value; lower U-value) while attempting to solve the issue of leaking seals. Their solutions all have four things in common: The units contain a vacuum between windows # 1  and # 2  to provide higher insulation than a fill gas; mechanical spacers are used to maintain the separation of the window lites (i.e., panes) # 1  and # 2  (if the lites come in physical contact with each other, this creates an undesirable thermal path that substantially reduces the IG unit&#39;s insulating value); the lites are hermetically sealed at their perimeters (most P commonly, using reflowed solder glass to seal two closely separated lites, and less commonly, using a laser to melt the two lites together); and all currently produced or described vacuum glazing units employ a tube (i.e., “pinch-tube”) to evacuate the IG unit, after which the tube is sealed shut. 
     These experimental solutions are not commercially available in the U.S. because they have failed or have not proven to be reliable. Problems include: the spacers are opaque or not aesthetically appealing so they fail to meet industry needs; laser attempts at sealing have resulted in broken lites due to thermal shocking of the glass; high thermal conductivity between the perimeter surfaces of the inside of the glass lites where they are sealed together; stress eventually causes either the seal or the lites to break because the sealing method is not compliant (flexible); elevated soldering temperatures eliminate the ability to use some soft-coat low-e coatings; and/or when a vacuum tube is added, it increases the unit&#39;s complexity and decreases its reliability. 
     A need therefor exists, for vacuum glazing units (VGUs) and insulated glass units (IGUs) having improved designs which address some of the aforesaid problems with the current technology. 
     SUMMARY OF THE INVENTION 
     The present invention disclosed herein comprises, in one aspect thereof, a hermetically sealed multi-pane window assembly. The window assembly comprises first and second windowpane sheets formed of transparent materials. A first sealing member has an inner edge and an outer edge, the inner edge being hermetically attached around the periphery of the first windowpane sheet by diffusion bonding. A second sealing member has an inner edge and an outer edge, the inner edge being hermetically attached around the periphery of the second windowpane sheet by diffusion bonding and the outer edge being hermetically attached to the outer edge of the first sealing member. A spacer assembly is disposed between the first and the second windowpane sheets for maintaining a gap therebetween, whereby a hermetically sealed cavity is defined between the first and the second windowpanes. 
     The present invention disclosed herein comprises, in another aspect thereof, a method for manufacturing a hermetically sealed multi-pane window assembly. A first windowpane sheet formed of a transparent material and having a periphery is provided, as is a first sealing member having an inner edge and an outer edge. The inner edge of the first sealing member is positioned against the first windowpane sheet. The inner edge of the first sealing member is pressed against the first windowpane sheet with sufficient force to produce a first predetermined contact pressure between the inner edge and the windowpane sheet along a first junction region. The first junction region is heated to produce a first predetermined temperature along the first junction region. The first predetermined contact pressure and an elevated temperature are maintained until a diffusion bond is formed between the first sealing member and the first windowpane sheet around the periphery of the first windowpane sheet. A second windowpane sheet formed of a transparent material and having a periphery is provided, as is a second sealing member having an inner edge and an outer edge. The inner edge of the second sealing member is positioned against the second windowpane sheet. The inner edge of the second sealing member is pressed against the second windowpane sheet with sufficient force to produce a second predetermined contact pressure between the inner edge and the windowpane sheet along a second junction region. The second junction region is heated to produce a second predetermined temperature along the second junction region. The second predetermined contact pressure and an elevated temperature are maintained until a diffusion bond is formed between the second sealing member and the second windowpane sheet around the periphery of the second windowpane sheet. A spacer assembly is positioned between the first and the second windowpane sheets for maintaining a gap therebetween. The outer end of the first sealing member is hermetically connected to the outer end of the second sealing member, whereby a hermetically sealed cavity is defined between the first and the second windowpanes. 
     The present invention disclosed herein comprises, in a further aspect thereof, a hermetically sealed multi-pane window assembly comprising a first windowpane formed of a transparent material and having a periphery. A first sealing member has an inner edge and an outer edge. The inner edge is hermetically sealed to the first windowpane around the periphery. A second windowpane is formed of a transparent material and has a periphery. The second windowpane is spaced-apart from the first windowpane. A second sealing member has an inner edge and an outer edge. The inner edge is hermetically sealed to the second windowpane around the periphery, and the outer edge is hermetically attached to the outer edge of the first sealing member. At least one of the first and second sealing members is compliant to enable relative movement between the first and second windowpanes. In this manner, a hermetically sealed cavity is formed between the first and the second windowpanes. 
     The present invention addresses many limitations of the prior art and, in various embodiments, provides VGUs and/or IGUs having some or all of the following advantages: diffusion bonding is used to make glass-to-metal, glass-to-glass and/or metal-to-metal bonds that are permanent, i.e., they cannot be disassembled by any known means such that the seals may last for up to 80 years; the hermetic sealing system incorporates a compliant (i.e., flexible) sleeve/frame unit (also called a “bellows”) that acts as springs, allowing the outside-facing window lite (window # 1 ) to expand and contract due to temperature changes independent of the inside-facing lite (window # 2 ); the metal sleeves are bonded to the glass lites using a glass-to-metal diffusion bonding process, and thus are more hermetic (gas-tight) than other known glass-to-metal seals; the thin, flexible metal sleeves have a high thermal resistance so that they do not adversely impact the overall insulating value; the windowpanes of the invention are able to use any currently employed glazing and coating, including low-e and UV-blocking coatings, and are also be compatible with electrochromeric coatings; units of the current invention can be thinner to reduce the weight and depth of the product, whether the application is a commercial window wall or a fenestration product; and spacer systems that are nearly invisible from any viewing angle. 
     Additional embodiments of the invention address the need for a drop-in replacement system for the single-pane glass units still used in the majority of U.S. buildings. IGUs of the invention can be thin enough to replace the 6 mm (¼″) thick single pane windows now in the majority of U.S. buildings, and may be economically installed so that vast numbers of owners could achieve significant heating and cooling energy reductions without incurring substantial window replacement costs. 
     Still further embodiments of the invention produce insulating windows addressing all of the DOE concerns and needs. In one such embodiment, the invention is an IGU that employs a partial vacuum instead of a fill gas to increase its insulating value. 
     In another embodiment, the invention comprises an IGU that contains a vacuum in the cavity between the pairs of windowpanes. A vacuum is the ultimate thermal insulator. The higher the level of vacuum, the fewer the molecules available to transfer heat between the pairs of windowpanes. Thus, window assemblies containing a vacuum instead of a gas will have the highest theoretical thermal insulation value (U-Value) of any window unit composed of two or more panes of glass or other materials. 
     In a further embodiment, the invention comprises an IGU having compliant (flexible) metal sleeves/frames (also known as “bellows”) that hermetically seal the IG unit, providing highest reliability while also possessing high thermal resistance (low thermal conductance) to minimize their impact on the unit&#39;s overall thermal performance. 
     In a still further embodiment, the invention comprises an IGU employing glass-to-metal diffusion bonding to bond the flexible metal sleeves to the glass lites (windows # 1  and # 2 ). This bond is permanent because it is molecular in nature, and is more hermetic than any other known attachment method. The IGU may contain and maintain a vacuum upwards of 80 years. 
     In yet another embodiment, the invention comprises an IGU that employs a unique glass spacer system of a glass substrate with glass standoffs on the top and bottom substrate surfaces. Any coatings that can be applied to surfaces # 2  or # 3  of known IGUs can instead be applied to either surface of the glass spacer substrate. IGU surfaces # 2  and # 3  can be coated with a scratch-resistant thin-film material such as diamond-like coatings (DLC) so that the differential movement of the glass spacers and the lites they support do not produce scratches on the lites&#39; inside surfaces. 
     In another embodiment, the invention comprises an IGU having thinner windows, which reduce the weight and depth of the fenestration products. Reducing the frame and associated construction materials will also reduce weight. 
     In a further embodiment, the invention comprises an IGU for residential and small commercial use that may be made as thin or thinner than the 6 mm (¼″) thick single-pane windows now installed in the majority of homes, thereby simplifying and/or reducing the cost of upgrading to a super insulating IG unit in existing fenestration products. 
     In a still further embodiment, the invention comprises an IGU that eliminates breakage due to bulging at high altitude. 
     The present invention disclosed and claimed herein comprises, in another aspect thereof, a frame assembly for hermetic attachment to one side of a sheet of transparent material having a plurality of window aperture areas defined thereon, each window aperture area being circumscribed by a frame attachment area having a predefined plan. The frame assembly comprises a plurality of continuous sidewalls circumscribing a plurality of frame apertures such that some sidewalls are disposed between two adjacent frame apertures. The sidewalls have an upper side plan configured to substantially correspond with the predefined plans of the frame attachment areas of the sheet. The sidewalls disposed between the adjacent frame apertures include two generally parallel sidewall members having an overall vertical thickness and a first connecting tab extending therebetween. When viewed in cross-section taken perpendicular to the plan view, the configuration of the sidewalls disposed between adjacent frame apertures is characterized by the first connecting tab having a relatively constant vertical thickness that is significantly smaller than the overall vertical thickness of the adjacent sidewall members. 
     The present invention disclosed and claimed herein comprises, in another aspect thereof, a frame assembly for hermetic attachment to one side of a sheet of transparent material having a plurality of window aperture areas defined thereon, each window aperture area being circumscribed by a frame attachment area having a predefined plan. The frame assembly comprises a first layer having a plan including a plurality of continuous sidewalls circumscribing a plurality of frame apertures such that some sidewalls are disposed between two adjacent frame apertures. The sidewalls have an upper side plan configured to substantially correspond with the predefined plans of the frame attachment areas of the sheet. A second layer has a plan including a plurality of continuous sidewalls. The sidewalls of the second layer have an upper side plan configured to at least partially overlap the plan of the sidewalls of the first layer all the way around each frame aperture. The first and second layers are joined to one another to create a hermetically gas-tight frame around each frame aperture. 
     The present invention disclosed and claimed herein comprises, in yet another aspect thereof, a hermetically sealed multi-pane window assembly. The window assembly comprises a spacer having a continuous sidewall circumscribing and thereby defining an aperture therethrough. The sidewall has an upper sealing surface and a lower sealing surface. The upper sealing surface is disposed on the upper side of the sidewall and continuously circumscribes the aperture, and the lower sealing surface is disposed on the lower side of the sidewall and continuously circumscribes the aperture. The window assembly further comprises a first and a second transparent windowpane sheets. The first sheet is disposed over at least a part of the upper sealing surface continuously around the aperture, and the second sheet is disposed over at least a part of the lower sealing surface continuously around the aperture, thereby defining a cavity enclosed by the sidewall and the windowpane sheets. The first and second transparent windowpane sheets are each hermetically bonded to the spacer without non-hermetic adhesives to form a continuous hermetic joint around the aperture. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a hermetically sealed micro-device package; 
         FIG. 2  is a cross-sectional view of the micro-device package of  FIG. 1 ; 
         FIG. 3  is an exploded view of a cover assembly manufactured in accordance with one embodiment of the current invention; 
         FIGS. 4   a  and  4   b  show transparent sheets having contoured sides, specifically: 
         FIG. 4   a  showing a sheet having both sides contoured; 
         FIG. 4   b  showing a sheet having one side contoured; 
         FIG. 5  shows an enlarged view of the sheet seal-ring area prior to metallization; 
         FIG. 6  shows an enlarged view of the sheet seal-ring area after metallization; 
         FIG. 7  shows a cross-sectional view through a pre-fabricated frame; 
         FIG. 8  illustrates placing the frame against the metallized sheet prior to bonding; 
         FIG. 9  is a block diagram of a process for manufacturing cover assemblies using prefabricated frames in accordance with one embodiment; 
         FIG. 10  is an exploded view of a cover assembly manufactured using a solder preform; 
         FIG. 11  is a partial perspective view of another embodiment utilizing solder applied by inkjet; 
         FIGS. 12   a - c  and  FIGS. 13   a - c  illustrate a process of manufacturing cover assemblies in accordance with yet another embodiment of the invention, specifically: 
         FIG. 12   a  shows the initial transparent sheet; 
         FIG. 12   b  shows the transparent sheet after initial metallization; 
         FIG. 12   c  shows the transparent sheet after deposition of the integral frame/heat spreader; 
         FIG. 13   a  shows a partial cross-section of the sheet of  FIG. 12   a;    
         FIG. 13   b  shows a partial cross-section of the sheet of  FIG. 12   b;    
         FIG. 13   c  shows a partial cross-section of the sheet of  FIG. 12   c;    
         FIG. 14  is a block diagram of a process for manufacturing cover assemblies using cold gas dynamic spray technology in accordance with another embodiment; 
         FIGS. 15   a - 15   b  illustrate a multi-unit assembly manufactured in accordance with another embodiment; specifically: 
         FIG. 15   a  illustrates an exploded view of a the multi-unit assembly; 
         FIG. 15   b  is bottom view of the frame of  FIG. 15   a;    
         FIG. 16   a  illustrates compliant tooling formed in accordance with another embodiment; 
         FIG. 16   b  is a side view of a multi-unit assembly illustrating the method of separation; 
         FIGS. 17   a  and  17   b  illustrate the manufacture of multiple cover assemblies in accordance with yet another embodiment, specifically: 
         FIG. 17   a  shows the transparent sheet in its original state; 
         FIG. 17   b  illustrates the sheet after deposition of the multi-aperture frame/heat spreader; 
         FIGS. 18   a - 18   c  illustrate an assembly configuration suitable for use with electrical resistance heating; specifically: 
         FIG. 18   a  illustrates the configuration of the sheet; 
         FIG. 18   b  illustrates the configuration of the frame; 
         FIG. 18   c  illustrates the joined sheet and frame; 
         FIGS. 19   a - 19   f  illustrate multi-unit assembly configurations suitable for heating with electrical resistance heating; 
         FIG. 20   a  illustrates an exploded view of a window assembly including interlayers for diffusion bonding; 
         FIG. 20   b  illustrates the window assembly of  FIG. 20   a  after diffusion bonding; 
         FIGS. 20   c  and  20   d  illustrate an additional embodiment of the invention having internal and external frames; specifically: 
         FIG. 20   c  illustrates an exploded view of a “sandwiched” window assembly before bonding; 
         FIG. 20   d  illustrates the completed assembly of  FIG. 20   c  after bonding; 
         FIGS. 20   e ,  20   f  and  20   g , illustrate fixtures for aligning and compressing the window assemblies during diffusion bonding; specifically: 
         FIG. 20   e  illustrates an empty fixture and clamps; 
         FIG. 20   f  illustrates the fixture of  FIG. 20   e  with a window assembly positioned therein for bonding; 
         FIG. 20   g  illustrates an alternative fixture designed to produce more axial pressure on the window assembly; 
         FIGS. 21   a - 21   b  are cross-sectional views of wafer-level hermetic micro-device packages in accordance with other embodiments of the invention; specifically: 
         FIG. 21   a  shows a wafer-level hermetic micro-device packages having reverse-side electrical connections; 
         FIG. 21   b  shows a wafer-level hermetic micro-device package having same-side electrical connections; 
         FIG. 21   c  is an exploded view illustrating the method of assembly of the package of  FIG. 21   b;    
         FIG. 22  illustrates a semiconductor wafer having a multiple micro-devices formed thereupon suitable for multiple simultaneous wafer-level packaging; 
         FIG. 23  illustrates the semiconductor wafer of  FIG. 22  after metallization of the wafer surface; 
         FIG. 24  illustrates a metallic frame for attachment between the wafer surface and the window sheet of a hermetic package; 
         FIGS. 25   a - 25   d  show enlarged views of the frame members of  FIG. 24 ; specifically: 
         FIG. 25   a  is a top view of a portion of a double frame member prior to singulation; 
         FIG. 25   b  is an end view of the double frame member of  FIG. 25   a;    
         FIG. 25   c  is a top view of a portion of a single frame member from the perimeter of the frame, or after device singulation; and 
         FIG. 25   d  is an end view of the single frame member of  FIG. 25   c;    
         FIG. 26  illustrates a metallized window sheet for attachment to the frame of  FIG. 24 ; 
         FIG. 27  shows a cross-sectional side view of a multiple-package assembly prior to singulation; 
         FIG. 28  illustrates one option for singulation of the multiple-package assembly of  FIG. 27 ; 
         FIG. 29  illustrates another option for singulation of the multiple-package assembly of  FIG. 27 ; 
         FIG. 30  illustrates a semiconductor wafer after metallization of the wafer surface in accordance with another embodiment having an electrode placement portion; 
         FIG. 31  illustrates a metallized window sheet in accordance with another embodiment having an electrode placement portion; 
         FIG. 32  is a cross-sectional side view of a multiple-package assembly prior to singulation in accordance with another embodiment having direct electrode access; 
         FIG. 33  is a top view of a micro-device with same-side pads; 
         FIG. 34  illustrates a semiconductor wafer having formed thereon a plurality of the micro-devices of  FIG. 33 ; 
         FIG. 35  illustrates the semiconductor wafer of  FIG. 34  after metallization of the wafer surface; 
         FIG. 36  illustrates a metallic frame for attachment to the wafer surface of  FIG. 35 ; 
         FIG. 37  illustrates a metallized window sheet for attachment to the frame of  FIG. 36 ; 
         FIG. 38  shows a top view a complete multiple-package assembly; 
         FIG. 39  illustrates a multi-package strip after column separation of the multiple-package assembly of  FIG. 38 ; 
         FIG. 40  illustrates a single packaged micro-device after singulation of the multiple-package strip of  FIG. 39 ; 
         FIG. 41  illustrates a partial cross-sectional side view of a multiple-package assembly having an alternative frame design prior to singulation; 
         FIGS. 42   a - 42   e  are cross-sectional side views of alternative frame designs, each showing a pair of adjacent frame side members joined by a connecting tab; 
         FIGS. 43   a - 43   e  are cross-sectional side views of additional alternative frame designs, each showing a pair of adjacent frame side members joined by one or more connecting tabs; 
         FIGS. 44   a - 44   e  are cross-sectional side views of further alternative frame designs, each showing a pair of adjacent frame side members joined by a connecting tab; 
         FIGS. 45   a - 45   f  are cross-sectional side views of still other alternative frame designs, each showing a pair of adjacent frame side members joined by one or more connecting tabs; 
         FIGS. 46   a - 46   d  are partial plan views of alternative frame designs, each showing a pair of adjacent frame side members joined by a connecting tab; 
         FIG. 47  is a plan view of a frame assembly fabricated by photo-chemical machining (PCM); 
         FIG. 48  is a cross-sectional side view of the frame assembly of  FIG. 47 ; 
         FIG. 49  is a perspective view of a PCM-fabricated multiple-frame array prior to singulation; 
         FIG. 50  is an exploded view of a double-pane hermetic window assembly; 
         FIG. 51  is a perspective view of the assembled double-pane hermetic window assembly of  FIG. 50 ; 
         FIG. 52  is an exploded view of a building window unit including two double-pane hermetic window assemblies; 
         FIG. 53  is a perspective view of the assembled building window unit of  FIG. 52 ; 
         FIG. 54  is an exploded view of a triple-pane hermetic window assembly; 
         FIG. 55  is a perspective view of the assembled triple-pane hermetic window assembly of  FIG. 54 ; 
         FIG. 56  illustrates the apparatus for fixturing multiple sets of hermetic window assemblies for simultaneous bonding; 
         FIG. 57  is a double-pane vacuum glazing unit (“VGU”) in accordance with the PRIOR ART; 
         FIG. 58   a  is an exploded view of the components of a vacuum glazing unit in accordance with one embodiment; 
         FIG. 58   b  is an assembled view of the VGU of  FIG. 58   a;    
         FIGS. 58   c ,  58   d  and  58   e  illustrate joining/bonding the upper frame member to the lower frame member; 
         FIG. 58   f  is a perspective view of a compliant frame in accordance with another embodiment; 
         FIG. 59   a  is an exploded view of the components of a vacuum glazing unit incorporating a woven spacer in accordance with another embodiment; 
         FIG. 59   b  is an assembled view of the VGU of  FIG. 59   a;    
         FIG. 60   a  exploded view of the components of a VGU with optional interlayers in accordance with another embodiment; 
         FIG. 60   b  is an assembled view of the VGU of  FIG. 60   a;    
         FIG. 61   a  is an exploded view of the components of a VGU with the spacers incorporated into the fabrication of the lower windowpane in accordance with another embodiment; 
         FIG. 61   b  is an assembled view of the VGU of  FIG. 61   a;    
         FIG. 62   a  is a side view of a windowpane with spacers on one of its surfaces that are incorporated into the windowpane&#39;s fabrication in accordance with another embodiment; 
         FIG. 62   b  is a first perspective view of the windowpane with spacers of  FIG. 62   a;    
         FIG. 62   c  is a second perspective view of the windowpane with spacers of  FIG. 62   a;    
         FIG. 63   a  is an exploded view of the components of a VGU with a transparent sheet center spacer unit that is fabricated with stand-offs on (as part of) the sheet&#39;s top and bottom sides in accordance with another embodiment; 
         FIG. 63   b  is an assembled view of the VGU of  FIG. 63   a;    
         FIG. 64   a  is an exploded view of the components of a VGU with an optional member between the sealed frame members and the windowpanes in accordance with another embodiment; 
         FIG. 64   b  is an assembled view of the VGU of  FIG. 64   a;    
         FIG. 65   a  is an exploded view of the components of a VGU with upper and lower frame members of similar shape and size in accordance with another embodiment; 
         FIG. 65   b  is an assembled view of the VGU of  FIG. 65   a;    
         FIGS. 66   a ,  66   b  and  66   c  show three variations on the “gull-wing” cross-sectional profile of the frame member; 
         FIG. 67   a  is a perspective view of an assembly of horizontal and vertical muntin bars in accordance with another embodiment; 
         FIG. 67   b  is a perspective view of an assembly of horizontal and vertical muntin bars with standoffs in accordance with another embodiment; 
         FIG. 67   c  is a side view of the muntin bar assembly of  FIG. 67   b;    
         FIG. 67   d  is an exploded view of the muntin bar assembly of  FIG. 67   b  positioned between the upper windowpane and the lower windowpane to form a sub-assembly; 
         FIG. 67   e  is an assembled perspective view of the sub-assembly of  FIG. 67   d;    
         FIG. 67   f  is an assembled side view of the sub-assembly of  FIG. 67   d;    
         FIG. 67   g  is an exploded view showing components of a VGU utilizing the muntin and windowpane sub-assembly of  FIG. 67   f;    
         FIG. 67   h  is an assembled view showing the VGU of  FIG. 67   g;    
         FIG. 68   a  is an exploded view of a VGU with frame members bonded to the inner (inside) surfaces of the windowpanes in accordance with another embodiment; 
         FIG. 68   b  is an assembled view showing the VGU of  FIG. 68   a;    
         FIG. 69   a  is an exploded view of a VGU with an internal muntin assembly and with inside-the windowpane bonded frame members that extend past the outer surfaces of the upper and lower windowpanes in accordance with another embodiment; 
         FIG. 69   b  is an assembled view showing the VGU of  FIG. 69   a;    
         FIG. 70   a  is an exploded view of a VGU with inside-the-windowpane bonded frame members and optional interlayers between the frame members and the windowpanes in accordance with another embodiment; 
         FIG. 70   b  is an assembled view showing the VGU of  FIG. 70   a;    
         FIG. 71   a  shows a VGU with a center spacer unit in accordance with another embodiment; 
         FIG. 71   b  shows a VGU with a center spacer unit and an intermediate frame member that is attached to the center spacer unit in accordance with yet another embodiment; 
         FIG. 71   c  shows a VGU with a center spacer unit and an intermediate frame member that is attached to the center spacer unit in accordance with a still further embodiment; 
         FIG. 72   a  is an exploded view of the components of a VGU with upper and lower windowpanes having built-on spacers and a flat center spacer in accordance with another embodiment; 
         FIG. 72   b  is an assembled view of the VGU of  FIG. 72   a;    
         FIG. 73   a  is an exploded view of the components of a vacuum glazing unit in accordance with another embodiment; 
         FIG. 73   b  is an assembled view of the VGU of  FIG. 73   a;    
         FIG. 73   c  is a perspective view of a compliant frame in accordance with another embodiment; 
         FIG. 74  is a side view of a spacer unit for a vacuum glazing unit in accordance with one embodiment; 
         FIG. 75  is a side view of a spacer unit for a vacuum glazing unit in accordance with another embodiment; 
         FIG. 76  is a side view of a spacer unit for a vacuum glazing unit in accordance with a further embodiment having “laminated” or “sandwiched” construction; 
         FIG. 77  is an enlarged elevation view of a portion of the spacer unit with cross-shaped stand-offs; 
         FIG. 78  is another elevation view of a portion of the spacer unit with cross-shaped stand-offs; 
         FIG. 79  is an enlarged elevation view of a portion of the spacer unit with “C”-shaped stand-offs. 
         FIG. 80  is a cross-sectional view of a two-lite IGU with spacer in accordance with another embodiment; 
         FIG. 81  is a cross-sectional view of a three-lite gas-filled IGU in accordance with another embodiment; 
         FIG. 82  is a cross-sectional view of a three-lite IGU with spacer in accordance with another embodiment; 
         FIG. 83  is a top view, with portions broken away, of the IGU of  FIG. 80 ; 
         FIG. 84  is a cross-sectional view of a two-lite IGU with spacer in accordance with another embodiment; 
         FIG. 85  is an enlarged cross-sectional perspective view of the spacer and retainer bar of  FIG. 84 ; 
         FIG. 86  is the spacer and retainer bar of  FIG. 85  showing the connection thereof; 
         FIG. 87  is a cross-sectional view of a three-lite IGU with inside frame mounting and spacers in accordance with another embodiment; 
         FIG. 88  is an enlarged portion of the IGU of  FIG. 87 ; 
         FIG. 89  is a cross-sectional view of a two-lite IGU with spacer in accordance with another embodiment; 
         FIG. 90  shows the IGU of  FIG. 89  supported by a mounting block in accordance with another embodiment; 
         FIG. 91   a  shows the IGU and mounting block of  FIG. 90  mounted in a frame; 
         FIG. 91   b  shows a unitary combined frame in accordance with another embodiment; 
         FIG. 92  is a perspective view of a portion of the mounting block of  FIG. 90 ; 
         FIG. 93  is a top view of a portion of the mounting block of  FIG. 92 ; 
         FIG. 94   a  shows a two-pane IGU having an anchored spacer in accordance with another embodiment; 
         FIG. 94   b  shows a two-pane IGU having no spacer in accordance with another embodiment; 
         FIG. 95  shows a three-pane IGU having split anchored spacers in accordance with still another embodiment; and 
         FIGS. 96   a ,  96   b  and  96   c  are perspective views showing assembly of an IGU with flexible spacers in accordance with another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The current invention is described below in greater detail with reference to certain preferred embodiments illustrated in the accompanying drawings. 
     Referring now to  FIGS. 1 and 2 , there is illustrated a typical hermetically sealed micro-device package for housing one or more micro-devices. For purposes of this application, the term “micro-device” includes photonic devices, photovoltaic devices, optical devices (i.e., including reflective, refractive and diffractive type devices), electro-optical and electro-optics devices (EO devices), light emitting devices (LEDs), liquid crystal displays (LCDs), liquid crystal on silicon (LCOS) technologies which includes direct drive image light amplifiers (D-ILA), opto-mechanical devices, micro-optoelectromechanical systems (i.e., MOEMS) devices and micro-electromechanical systems (i.e., MEMS) devices. The package  102  comprises a base or substrate  104 , which is hermetically sealed to a cover assembly  106  comprising a frame  108  and a transparent window  110 . A micro-device  112  mounted on the base  104  is encapsulated within a cavity  114  when the cover assembly  106  is joined to the base  104 . One or more electrical leads  116  may pass through the base  104  to carry power, ground, and signals to and from the micro-device  112  inside the package  102 . It will be appreciated that the electrical leads  116  must also be hermetically sealed to maintain the integrity of the package  102 . The window  110  is formed of an optically or electro-magnetically transparent material. For purposes of this application, the term “transparent” refers to materials, which allow the transmission of electromagnetic radiation having predetermined wavelengths, including, but not limited to, visible light, infrared light, ultraviolet light, microwaves, radio waves, or x-rays. The frame  108  is formed from a material, typically a metal alloy, which preferably has a CTE close to that of both the window  110  and the package base  104 . 
     Referring now to  FIG. 3 , there is illustrated an exploded view of a cover assembly manufactured in accordance with one embodiment of the current invention. The cover assembly  300  includes a frame  302  and a sheet  304  of a transparent material. The frame  302  has a continuous sidewall  306 , which defines a frame aperture  308  passing therethrough. The frame sidewall  306  includes a frame seal-ring area  310  (denoted by crosshatching) circumscribing the frame aperture  308 . Since the frame  302  will eventually be welded to the package base  104  (from FIGS.  1  and  2 ,) it is usually formed of a weldable metal or alloy, preferably one having a CTE very close to that of the micro-device package base  104 . In some embodiments, however, the cover assembly frame  304  may be formed of a non-metallic material such as ceramic or alumina. Regardless of whether the frame  302  is formed of a metallic or non-metallic material, the surface of the frame seal-ring area  310  is preferably metallic (e.g., metal plated if not solid metal) to facilitate the hermetic sealing of the sheet  304  to the frame. In a preferred embodiment, the frame is primarily formed of an alloy having a nominal chemical composition of 54% iron (Fe), 29% nickel (Ni) and 17% cobalt (Co). Such alloys are also known by the designation ASTM F-15 alloy and by the trade name Kovar Alloy. As used in this application, the term “Kovar Alloy” will be understood to mean the alloy having the chemical composition just described. In embodiments where a Kovar Alloy frame  302  is used, it is preferred that the surface of the frame seal-ring area  310  have a surface layer of gold (Au) overlying a layer of nickel (Ni), or a layer of nickel without the overlaying gold. The frame  302  also includes a base seal area  320 , which is adapted for eventual joining, typically by welding, to the package base  104 . The base seal area  320  frequently includes a layer of nickel overlaid by a layer of gold to facilitate seam welding to the package base. Although the gold over nickel surface layers are only required along the base seal-ring area  320 , it will be appreciated that in many cases, for example, where solution bath plating is used to apply the surface materials, the gold over nickel layers may be applied to the entire surface of the frame  302 . The sheet  304  can be any type of transparent material, for example, soft glass (e.g., soda-lime glass), hard glass (e.g. borosilicate glass), crystalline materials such as quartz and sapphire, or polymeric materials such as polycarbonate plastic. In addition to optically transparent materials, the sheet  304  may be visibly opaque but transparent to non-visible wavelengths of energy. As previously discussed, it is preferred that the material of the sheet  304  have a CTE that is similar to that of the frame  304  and of the package base  104  to which the cover assembly will eventually be attached. For many semiconductor photonic, photovoltaic, MEMS or MOEMS applications, a borosilicate glass is well suited for the material of the sheet  304 . Examples of suitable glasses include Corning 7052, 7050, 7055, 7056, 7058, 7062, Kimble (Owens Corning) EN-1, and Kimble K650 and K704. Other suitable glasses include Abrisa soda-lime glass, Schott 8245 and Ohara Corporation S-LAM60. 
     The sheet  304  has a window portion  312  defined thereupon, i.e., this is the portion of the sheet  302  which must remain transparent to allow for the proper functioning of the encapsulated, i.e., packaged, micro-device  112 . The window portion  312  of the sheet has top and bottom surfaces  314  and  316 , respectively, that are optically finished in the preferred embodiment. The sheet  304  is preferably obtained with the top and bottom surfaces  314  and  316  of the window portion  312  in ready to use form, however, if necessary the material may be ground and polished or otherwise shaped to the desired surface contour and finish as a preliminary step of the manufacturing process. While in many cases the window portion  312  will have top and bottom surfaces of  314  and  316  that are optically flat and parallel to one another, it will be appreciated that in other embodiments at least one of the finished surfaces of the window portion will be contoured. A sheet seal-ring area  318  (denoted with cross-hatching) circumscribes the window portion  312  of the sheet  304 , and provides a suitable surface for joining to the front seal-ring area  310 . 
     Referring now to  FIGS. 4   a  and  4   b , there are illustrated transparent sheets having contoured sides. In  FIG. 4   a , transparent sheet  304 ′ has both a curved top side  314 ′ and a curved bottom side  316 ′ producing a window portion  312  having a curved contour with a constant thickness. In  FIG. 4   b , sheet  304  has a top side  314 , which is curved, and a bottom side  316 , which is flat, thereby resulting in a window portion  312  having a plano-convex lens arrangement. It will be appreciated that in similar fashion (not illustrated) the finished surfaces  314  and  316  of the window portion  312  can have the configuration of a refractive lens including a plano-convex lens as previously illustrated, a double convex lens, a plano-concave lens or a double concave lens. Other surface contours may give the finished surfaces of the window portion  312  the configuration of a Fresnel lens or of a diffraction grating, i.e., “a diffractive lens.” 
     In many applications, it is desirable that window portion  312  of the sheet  304  have enhanced optical or physical properties. To achieve these properties, surface treatments or coatings may be applied to the sheet  304  prior to or during the assembly process. For example, the sheet  304  may be treated with siliconoxynitride (SiOn) to provide a harder surface on the window material. Whether or not treated with SiOn, the sheet  304  may be coated with a scratch resistant/abrasion resistant material such as amorphous diamond-like carbon (DLC) such as that sold by Diamonex, Inc., under the name Diamond Shield®. Other coatings which may be applied in addition to, or instead of, the SiOn or diamond-like carbon include, but are not limited to, optical coatings, anti-reflective coatings, refractive coatings, achromatic coatings, optical filters, solar energy filters or reflectors, electromagnetic interference (EMI) and radio frequency (RF) filters of the type known for use on lenses, windows and other optical elements. It will be appreciated that the optical coatings and/or surface treatments can be applied either on the top surface  314  or the bottom surface  316 , or in combination on both surfaces, of the window portion  312 . It will be further appreciated, that the optical coatings and treatments just described are not illustrated in the figures due to their transparent nature. 
     In some applications, a visible aperture is formed around the window portion  312  of the sheet  304  by first depositing a layer of non-transparent material, e.g., chromium (Cr), sometimes coating the material over the entire surface of the sheet and then etching the non-transparent material from the desired aperture area. This procedure provides a sharply defined border to the window portion  312 , which is desirable in some applications. This operation may be performed prior to or after the application of other treatments depending on the compatibility and processing economics. 
     The next step of the process of manufacturing the cover assembly  300  is to prepare the sheet seal-ring area  318  for metallization. The sheet seal-ring area  318  circumscribes the window portion  312  of the sheet  304 , and for single aperture covers is typically disposed about the perimeter of the bottom surface  316 . It will be appreciated, however, that in some embodiments the sheet seal-ring area  318  can be located in the interior portion of a sheet, for example where the sheet will be diced to form multiple cover assemblies (i.e., as described later herein). The sheet seal-ring area  318  generally has a configuration, which closely matches the configuration of the frame seal-ring area  310  to which it will eventually be joined. Preparing the sheet seal-ring area  318  may involve a thorough cleaning to remove any greases, oils or other contaminants from the surface, and/or it may involve roughening the seal-ring area by chemical etching, laser ablating, mechanical grinding or sandblasting this area. This roughening increases the surface area of the sheet seal-ring, thereby providing increased adhesion for the subsequently deposited metallization materials, if the sheet seal-ring is to be metallized prior to joining to the frame seal-ring area  310  or to other substrates or device package bases. 
     Referring now to  FIG. 5 , there is illustrated a portion of the sheet  304  which has been placed bottom side up to better illustrate the preparation of the sheet seal-ring area  318 . In this example the seal-ring area  318  has been given a roughened surface  501  to improve adhesion of the metallic layers to be applied. Chemical etching to roughen glass and similar transparent materials is well known. Alternatively, laser ablating, conventional mechanical grinding or sandblasting may be used. A grinding wheel with 325 grit is believed suitable for most glass materials, while a diamond grinding wheel may be used for sapphire and other hardened materials. The depth  502  to which the roughened surface  501  of the sheet seal-ring area  318  penetrates the sheet  304  is dependent on at least two factors: first, the desired mounting height of the bottom surface  316  of the window relative to the package bottom and/or the micro-device  112  mounted inside the package; and second, the required thickness of the frame  306  including all of the deposited metal layers (described below). It is believed that etching or grinding the sheet seal-ring area  318  to a depth of  502  within the range from about 0 inches to about 0.05 inches will provide a satisfactory adhesion for the metallized layers as well as providing an easily detectable “lip” for locating the sheet  304  in the proper position against the frame  306  during subsequent joining operations. 
     It will be appreciated that it may be necessary or desirable to protect the finished surfaces  314  and/or  316  in the window portion  312  of the sheet (e.g., the portions that will be optically active in the finished cover assembly) from damage during the roughening process. If so, the surfaces  314  and/or  316  may be covered with semiconductor-grade “tacky tape” or other known masking materials prior to roughening. The mask material must, of course, be removed in areas where the etching/grinding will take place. Sandblasting is probably the most economical method of selectively removing strips of tape or masking material in the regions that will be roughened. If sandblasting is used, it could simultaneously perform the tape removal operation and the roughening of the underlying sheet. 
     Referring now to  FIG. 6 , there is illustrated a view of the seal-ring area  318  of the sheet  304  after metallization. The next step of the manufacturing process may be to apply one or more metallic layers to the prepared sheet seal-ring area  318 . The current invention contemplates several options for accomplishing this metallization. A first option is to apply metal layers to the sheet seal-ring area  318  using conventional chemical vapor deposition (CVD) technology. CVD technology includes atmospheric pressure chemical vapor deposition (APCVD), low pressure chemical vapor deposition (LPCVD), plasma assisted (enhanced) chemical vapor deposition (PACVD, PECVD), photochemical vapor deposition (PCVD), laser chemical vapor deposition (LCVD), metal-organic chemical vapor deposition (MOCVD) and chemical beam epitaxy (CBE). A second option for metallizing the roughened seal-ring area  318  is using physical vapor deposition (PVD) technology. PVD technology includes sputtering, ion plasma assist, thermal evaporation, vacuum evaporation, and molecular beam epitaxy (MBE). A third option for metallizing the roughened sheet seal-ring area  318  is using solution bath plating technology (SBP). Solution bath plating includes electroplating, electroless plating and electrolytic plating technology. While solution bath plating cannot be used for depositing the initial metal layer onto a nonmetallic surface such as glass or plastic, it can be used for depositing subsequent layers of metal or metal alloy to the initial layer. Further, it is envisioned that in many cases, solution bath plating will be the most cost effective metal deposition technique. Since the use of chemical vapor deposition, physical vapor deposition and solution bath plating to deposit metals and metal alloys is well known, these techniques will not be further described herein. 
     A fourth option for metallizing the sheet seal-ring area  318  of the sheet  304  is so-called cold-gas dynamic spray technology, also known as “cold-spray”. This technology involves the spraying of powdered metals, alloys, or mixtures of metal and alloys onto an article using a jet of high velocity gas to form continuous metallic coating at temperatures well below the fusing temperatures of the powdered material. Details of the cold-gas dynamic spray deposition technology are disclosed in U.S. Pat. No. 5,302,414 to Alkhimov et al. It has been determined that aluminum provides good results when applied to glass using the cold-gas dynamic spray deposition. The aluminum layer adheres extremely well to the glass and may create a chemical bond in the form of aluminum silicate. However, other materials may also be applied as a first layer using cold-spray, including tin, zinc, silver and gold. Since the cold-gas dynamic spray technology can be used at low temperatures (e.g., near room temperature), it is suitable for metallizing materials having a relatively low melting point, such as polycarbonates or other plastics, as well as for metallizing conventional materials such as glass, alumina, and ceramics. 
     For the initial metallic layer deposited on the sheet  304 , it is believed that any of chromium, nickel, aluminum, tin, tin-bismuth alloy, gold, gold-tin alloy can be used, this list being given in what is believed to be the order of increasing adhesion to glass. Other materials might also be appropriate. Any of these materials can be applied to the sheet seal-ring area  318  using any of the CVD or PVD technologies (e.g., sputtering) previously described. After the initial layer  602  is deposited onto the sheet seal-ring area  318  of the nonmetallic sheet  304 , additional metal layers, e.g., second layer  604 , third layer  606  and fourth layer  608  (as applicable) can be added by any of the deposition methods previously described, including solution bath plating. It is believed that the application of the following rules will result in satisfactory thicknesses for the various metal layers. Rule No. 1: the minimum thickness, except for the aluminum or tin-based metals or alloys, which will be bonded to the gold-plated Kovar alloy frame: 0.002 microns. Rule 2: the minimum thickness for aluminum or tin-based metals or alloys deposited onto the sheet or as the final layer, which will be bonded to the gold-plated Kovar alloy frame: 0.8 microns. Rule 3: the maximum thickness for aluminum or tin-based metals or alloys deposited onto the sheet or as the final layer, which will be bonded to the gold-plated Kovar alloy frame: 63.5 microns. Rule 4: the maximum thickness for metals, other than chromium, deposited onto the sheet as the first layer and which will have other metals or alloys deposited on top of them: 25 microns. Rule 5: the maximum thickness for metals, other than chromium, deposited onto other metals or alloys as intermediate layers: 6.35 microns. Rule 6: the minimum thickness for metals or alloys deposited onto the sheet or as the final layer, which will act as the solder for attachment to the gold-plated Kovar alloy frame: 7.62 microns. Rule 7: the maximum thickness for metals or alloys deposited onto the sheet or as the final layer, which will act as the solder for attachment to the gold-plated Kovar alloy frame: 101.6 microns. Rule 8: the maximum thickness for chromium: 0.25 microns. Rule 9: the minimum thickness for gold-tin solder, applied via inkjet or supplied as a solder preform: 6 microns. Rule 10: the maximum thickness for gold-tin solder, applied via inkjet or supplied as a solder preform: 101.6 microns. Rule 11: The minimum thickness for immersion zinc; 0.889 microns. Note that the above rules apply to metals deposited using all deposition methods other than cold-gas dynamic spray deposition. 
     For cold spray applications, the following rules apply: Rule 1: the minimum practical thickness for any metal layer: 2.54 microns. Rule 2: the maximum practical thickness for the first layer, and all additional layers, but not including the final Kovar alloy layer: 127 microns. Rule 3: the maximum practical thickness for the final Kovar alloy layer: 12,700 microns, i.e., 0.5 inches. 
     By way of example, not to be considered limiting, the following metal combinations are believed suitable for seal-ring area  318  when bonding the prepared sheet  304  to a Kovar alloy-nickel-gold frame  302  (i.e., Kovar alloy core plated first with nickel and then with gold) using thermal compression (TC) bonding, or sonic, ultrasonic or thermosonic bonding. 
     The assembly sequence can also be to first bond the frame/spacer and window sheet together to form a hermetically sealed window unit, and later, to bond this window unit to the substrate. A third assembly sequence can also be to first bond the frame/spacer and substrate together and later, to bond this substrate/frame/spacer unit to the window. In some instances, an intermediate material, also referred to as an interlayer material, may be employed between the substrate and the frame/spacer and/or between the frame/spacer and the window sheet. It will be understood that, while the examples described herein are believed suitable for metallizing the seal-ring surface of a sheet or lens prior to bonding in applications where metallization is used, in some other embodiments employing diffusion bonding (i.e., thermal compression bonding), metallization of the seal-ring area on the sheet or lens may be omitted altogether when joining the sheet/lens to the frame or another substrate of the device package base. 
     Example 1 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 A1 
                 CVD, PVD 
                 0.7 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 2 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.002 
                 25 
               
               
                 2 
                 Cu 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Sn or SnBi 
                 CVD, PVD, SBP 
                 0.7 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 3 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.002 
                 25 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Sn or Sn—Bi 
                 CVD, PVD, SBP 
                 0.7 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 4 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.002 
                 25 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Sn or Sn—Bi 
                 CVD, PVD, SBP 
                 0.7 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 5 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Sn (de-stressed) 
                 CVD, PVD 
                 0.002 
                 25 
               
               
                 2 
                 Cu 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Sn or Sn—Bi 
                 CVD, PVD, SBP 
                 0.7 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 6 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Sn—Bi 
                 CVD, PVD 
                 0.7 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 7 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.002 
                 0.15 
               
               
                 2 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Sn or Sn—Bi 
                 CVD, PVD, SBP 
                 0.7 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 8 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.002 
                 0.15 
               
               
                 2 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Al 
                 CVD, PVD, SBP 
                 0.7 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 9 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.002 
                 0.15 
               
               
                 2 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Zn 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Al 
                 CVD, PVD, SBP 
                 0.7 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 10 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.002 
                 152.4 
               
               
                 2 
                 Sn or Sn—Bi 
                 CVD, PVD, SBP 
                 0.7 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 11 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.002 
                 152.4 
               
               
                 2 
                 Al 
                 CVD, PVD, SBP 
                 0.7 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 12 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.002 
                 152.4 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 A1 
                 CVD, PVD, SBP 
                 0.7 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 13 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Sn 
                 CVD, PVD 
                 0.7 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 14 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.002 
                 0.15 
               
               
                   
               
            
           
         
       
     
     Example 15 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.002 
                 152.4 
               
               
                   
               
            
           
         
       
     
     Example 16 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Sn—Bi 
                 CVD, PVD 
                 0.7 
                 63.5 
               
               
                   
               
            
           
         
       
     
     By way of further example, not to be considered limiting, the following metal combinations and thicknesses are preferred for seal-ring area  318  when bonding the prepared sheet  304  to a Kovar alloy-nickel-gold frame  302  using thermal compression (TC) bonding, or sonic, ultrasonic or thermosonic bonding. 
     Example 17 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 A1 
                 CVD, PVD 
                 1 
                 50.8 
               
               
                   
               
            
           
         
       
     
     Example 18 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.1 
                 2.54 
               
               
                 2 
                 Cu 
                 CVD, PVD, SBP 
                 0.25 
                 2.54 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Sn or SnBi 
                 CVD, PVD, SBP 
                 1 
                 50.8 
               
               
                   
               
            
           
         
       
     
     Example 19 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.1 
                 2.54 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.3175 
                 5.08 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Sn or Sn—Bi 
                 CVD, PVD, SBP 
                 1 
                 50.8 
               
               
                   
               
            
           
         
       
     
     Example 20 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.1 
                 2.54 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.3175 
                 5.08 
               
               
                 3 
                 Sn or Sn—Bi 
                 CVD, PVD, SBP 
                 1 
                 50.8 
               
               
                   
               
            
           
         
       
     
     Example 21 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Sn (de-stressed) 
                 CVD, PVD 
                 0.1 
                 2.54 
               
               
                 2 
                 Cu 
                 CVD, PVD, SBP 
                 0.25 
                 2.54 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Sn or Sn—Bi 
                 CVD, PVD, SBP 
                 1 
                 50.8 
               
               
                   
               
            
           
         
       
     
     Example 22 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Sn—Bi 
                 CVD, PVD 
                 1 
                 50.8 
               
               
                   
               
            
           
         
       
     
     Example 23 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                 2 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 3 
                 Sn or Sn—Bi 
                 CVD, PVD, SBP 
                 1 
                 50.8 
               
               
                   
               
            
           
         
       
     
     Example 24 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                 2 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 3 
                 Al 
                 CVD, PVD, SBP 
                 1 
                 50.8 
               
               
                   
               
            
           
         
       
     
     Example 25 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                 2 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 3 
                 Zn 
                 CVD, PVD, SBP 
                 0.3175 
                 5.08 
               
               
                 4 
                 Al 
                 CVD, PVD, SBP 
                 1 
                 50.8 
               
               
                   
               
            
           
         
       
     
     Example 26 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.1 
                 5.08 
               
               
                 2 
                 Sn or Sn—Bi 
                 CVD, PVD, SBP 
                 1 
                 50.8 
               
               
                   
               
            
           
         
       
     
     Example 27 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.1 
                 5.08 
               
               
                 2 
                 A1 
                 CVD, PVD, SBP 
                 1 
                 50.8 
               
               
                   
               
            
           
         
       
     
     Example 28 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.1 
                 5.08 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.3175 
                 5.08 
               
               
                 3 
                 A1 
                 CVD, PVD, SBP 
                 1 
                 50.8 
               
               
                   
               
            
           
         
       
     
     Example 29 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Sn 
                 CVD, PVD 
                 1 
                 50.8 
               
               
                   
               
            
           
         
       
     
     Example 30 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                   
               
            
           
         
       
     
     Example 31 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.1 
                 50.8 
               
               
                   
               
            
           
         
       
     
     Example 32 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Sn—Bi 
                 CVD, PVD 
                 1 
                 50.8 
               
               
                   
               
            
           
         
       
     
     As indicated above, the previous examples are believed suitable for application of, among other processes, thermal compression bonding. TC bonding is a process of diffusion bonding in which two prepared surfaces are brought into intimate contact, and plastic deformation is induced by the combined effect of pressure and temperature, which in turn results in atom movement causing the development of a crystal lattice bridging the gap between facing surfaces and resulting in bonding. TC bonding can take place at significantly lower temperatures than many other forms of bonding such as braze soldering. 
     Referring now to  FIG. 7 , there is illustrated a cross-sectional view of the prefabricated frame  302  suitable for use in this embodiment. The illustrated frame  302  includes a Kovar alloy core  702 , or a core of different metal or alloy, overlaid with a first metallic layer  704  of nickel which, in turn, is overlaid by an outer layer  706  of gold. The use of Kovar alloy for the core  702  of the frame  302  may be preferred where hard glass, e.g., Corning 7056 or 7058, is used for the sheet  304  and where Kovar alloy or a similar material is used for the package base  104 , since these materials have a CTE for the temperature range 30° C. to 300° C. that is within the range from about 5.0-10 −6 /° K to about 5.6-10 −6 /° K (e.g., from about 5.0 to about 5.6 ppm/° K). 
     Referring still to  FIG. 7 , another step of the manufacturing process is the preparation of a prefabricated frame  302  for joining to the sheet  304 . As previously described, the frame  302  includes a continuous sidewall  306 , which defines an aperture  308  therethrough. The sidewall  306  includes a frame seal-ring area  310  on its upper surface and a base seal-ring area  320  on its lower surface. The frame seal-ring area  310  is generally dimensioned to conform with the sheet seal-ring area  318  of the transparent sheet  304 , while the base seal-ring area  320  is generally dimensioned to conform against the corresponding seal area on the package base. The frame  302  may be manufactured using various conventional metal forming technologies, including stamping, casting, die casting, extrusion/parting, and machining. It is contemplated that stamping or die casting may be the most cost effective method for producing the frames  302 . However, fabricating the frame  302  using photo-chemical machining (PCM), also known as chemical etching, may, in some instances be the most economical method. In some instances, several sheets of photo-chemical machined (i.e., etched) metals and/or alloy might be bonded together to form the frame  302 . One of the bonding methods includes TC bonding, also known as diffusion bonding, the PCM&#39;d layers together to create the frame  302 . Depending upon the degree of flatness required for the contemplated bonding procedure and the degree achieved by a particular frame manufacturing method, surface grinding, and possibly even lapping or polishing, may be required on the frame seal-ring area  310  or base seal-ring area  320 , to provide the final flatness necessary for a successful hermetic seal. 
     In this example, the base seal-ring area  320  is on the frame face opposite frame seal-ring area  310 , and may utilize the same layers of nickel  704  overlaid by gold  706  to facilitate eventual welding to the package base  104 . In some instances, the gold  706  will not be overlaid on the nickel  704 . 
     In some embodiments, the frame  302  will serve as a “heat sink” and/or “heat spreader” when the cover assembly  300  is eventually welded to the package base  104 . It is contemplated that conventional high temperature welding processes (e.g., manual or automatic electrical resistance seam welding or laser welding) may be used for this operation. If the metallized glass sheet  304  were welded directly to the package base  104  using these welding processes, the concentrated heat could cause thermal stresses likely to crack the glass sheet or distort its optical properties. However, when a metal frame is attached to the transparent sheet, it acts as both a heat sink, absorbing some of the heat of welding, and as a heat spreader, distributing the heat over a wider area such that the thermal stress on the transparent sheet  304  is reduced to minimize the likelihood of cracking or optical distortion. Kovar alloy is especially useful in this heat sink and heat spreading role as explained by Kovar alloy&#39;s thermal conductivity, 0.0395, which is approximately fourteen times higher than the thermal conductivity of Corning 7052 glass, 0.0028. 
     Another important aspect of the frame  302  is that it should be formed from a material having a CTE that is similar to the CTE of the transparent sheet  304  and the CTE of the package base  104 . This matching of CTE between the frame  302 , transparent sheet  304  and package base  104  is beneficial to minimize stresses between these components after they are joined to one another so as to ensure the long term reliability of the hermetic seal therebetween under conditions of thermal cycling and/or thermal shock environments. 
     For window assemblies that will be attached to package bases formed of ceramic, alumina or Kovar alloy, Kovar alloy is preferred for use as the material for the frame  304 . Although Kovar alloy will be used for the frames in many of the embodiments discussed in detail herein, it will be understood that Kovar alloy is not necessarily suitable for use with all transparent sheet materials. Additionally, other frame materials besides Kovar alloy may be suitable for use with glass. Suitability is determined by the desire that the material of the transparent sheet  304 , the material of the frame  302  and the material of the package base  104  all have closely matching CTEs to insure maximum long-term reliability of the hermetic seals. 
     Referring now to  FIG. 8 , the next step of the manufacturing process is to position the frame  302  against the sheet  304  such that at least a portion of the frame seal-ring area  310  and a least a portion of the sheet seal-ring area  318  contact one another along a continuous junction region  804  that circumscribes the window portion  312 . Actually, in some cases a plasma-cleaning operation and/or a solvent or detergent cleaning operation is performed on the seal-ring areas and any other sealing surfaces just prior to joining the components to ensure maximum reliability of the joint. In  FIG. 8 , the sheet  304  moves from its original position (denoted in broken lines) until it is in contact with the frame  302 . It is, of course, first necessary to remove any remaining tacky tape or other masking materials left over from operations used to prepare the sheet seal-ring area  318  if they cannot withstand the elevated temperatures encountered in the joining process without degradation of the mask material and/or its adhesive, if an adhesive is used to attach the mask to the sheet. It will be appreciated that it is not necessary that the sheet seal-ring area  318  and the frame seal-ring area  310  have an exact correspondence with regard to their entire areas, rather, it is only necessary that there be some correspondence between the two seal-ring areas forming a continuous junction region  804 , which circumscribes the window portion  312 . In the embodiment illustrated in  FIG. 8 , the metallized layers  610  in the sheet seal-ring area  318  are much wider than the plated outer layer  706  of the frame seal-ring area  310 . Further, the window portion  312  of the sheet  304  extends partway through the frame aperture  308 , providing a means to center the sheet  304  on the frame  302 . 
     The next step of the manufacturing process is to heat the junction region  804  until a joint is formed between the frame  302  and the sheet  304  all along the junction region, whereby a hermetic seal circumscribing the window portion  312  is formed. It is necessary that during the step of heating the junction region  804 , the temperature of the window portion  312  of the sheet  304  remain below its glass transition temperature, T G  as well as below the softening temperature of the sheet  304 , to prevent damage to the finished surfaces  314  and  316 . The softening point for glass is defined as the temperature at which the glass has a viscosity of 107.6 dPa s or 107.6 poise (method of measurement: ISO 7884-3). The current invention contemplates several options for accomplishing this heating. A first option is to utilize thermal compression (TC) bonding, also known as diffusion bonding, including conventional hot press bonding as well as Hot Isostatic Press or Hot Isostatic Processing (HIP) diffusion bonding. As previously described, TC bonding, also known as diffusion bonding involves the application of high pressures to the materials being joined such that a reduced temperature is required to produce the necessary diffusion bond. Rules for determining the thickness and composition of the metallic layers  610  on the sheet  304  were previously provided, for TC bonding to, e.g., a Kovar alloy, nickel or gold frame such as illustrated in  FIG. 7 . The estimated process parameters for the TC bonding of a Kovar alloy/nickel/gold frame  302  to a metallized sheet  304  having aluminum as the final layer would be a temperature of approximately 380° C. at an applied pressure of approximately 95,500 psi (6713.65 kg/cm 2 ). Under these conditions, the gold plating  706  on the Kovar alloy frame  302  will diffuse into/with the aluminum layer, e.g., layer 4 in Example 7. Since the 380° C. temperature necessary for TC bonding is below the approximately 500° C. to 900° C. T G  for hard glasses such as Corning 7056, the TC bonding process could be performed in a single or batch mode by fixturing the cover assembly components  302 ,  304  together in compression and placing the compressed assemblies into a furnace (or oven, etc.) at approximately 380° C. The hermetic bond would be obtained without risking the finished surfaces  314  and  316  of the window portion  312 . Vacuum, sometimes with some small amounts of specific gasses included, or other atmospheres with negative or positive pressures might be needed inside the furnace to promote the TC bonding process. 
     Alternatively, employing resistance welding at the junction area  804  to add additional heat in addition to the TC bonding could allow preheating the window assemblies to less than 380° C. and possibly reduce the overall bonding process time. In another method, the TC bonding could be accomplished by fixturing the cover assembly components  302  and  304  using heated tooling that would heat the junction area  304  by conduction. In yet another alternative method, electrical resistance welding can be used to supply 100% of the heat required to achieve the necessary TC bonding temperature, thereby eliminating the need for furnaces, ovens, etc. or specialized thermally conductive tooling. 
     After completion of TC bonding or other welding processes, the window assembly  300  is ready for final processing, for example, chamfering the edges of the cover assembly to smooth them and prevent chipping, scratching, marking, etc., during post-assembly, cleaning, marking or other operations. In some instances, the final processing may include the application of a variety of coatings to the window and/or to the frame. 
     Referring now to  FIG. 9 , there is illustrated a block diagram of the manufacturing process just described in accordance with one embodiment of the current invention. Block  902  represents the step of obtaining a sheet of transparent material, e.g., glass or other material, having finished top and bottom surfaces as previously described. The process then proceeds to block  904  as indicated by the arrow. 
     Block  904  represents the step of applying surface treatments to the sheet, e.g., scratch-resistant or anti-reflective coatings, as previously described. In addition to these permanent surface treatments, block  904  also represents the sub-steps of applying tape or other temporary masks to the surfaces of the sheet to protect them during the subsequent steps of the process. It will be appreciated that the steps represented by block  904  are optional and that one or more of these steps may not be present in every embodiment of the invention. The process then proceeds to block  906  as indicated by the arrow. 
     Block  906  represents the step of preparing the seal-ring area on the sheet to provide better adhesion for the metallic layers, if such metallic layers are used. This step usually involves roughening the seal-ring area using chemical etching, mechanical grinding, laser ablating or sandblasting as previously described. To the extent necessary, block  906  also represents the sub-steps of removing any masking material from the seal-ring area. Block  906  further represents the optional steps of cleaning the sheet (or at least the seal-ring area of the sheet) to remove any greases, oils or other contaminants from the surface of the sheet. As previously discussed, such cleaning steps may be performed regardless of whether the seal-ring area is to be metallized (i.e., to promote better adhesion of the metallic layers) or is to be left unmetallized (i.e., to promote better diffusion bonding of the unmetallized sheet). It will be appreciated that the steps represented by block  906  are optional and that some or all of these steps may not be present in every embodiment of the invention. The process then proceeds to block  908  as indicated by the arrow. 
     Block  908  represents the step of metallizing the seal-ring areas of the sheet. The step represented by block  908  is mandatory only when the desired bond of sheet  304  to frame  302  is a metal-to-metal bond since at least one metallic layer must be applied to the seal-ring area of the sheet. It is possible, for instance by use of diffusion bonding processes, to bond the sheet  304  to frame  302  without first metallizing sheet  304 . In most embodiments, block  908  will represent numerous sub-steps for applying successive metallic layers to the sheet, where the layers of each sub-step may be applied by processes including CVD, PVD, cold-spray or solution bath plating as previously described. Following the steps represented by block  908 , the sheet is ready for joining to the frame. However, before the process can proceed to this joining step (i.e., block  916 ), a suitable frame must first be prepared. 
     Block  910  represents the step of obtaining a pre-fabricated frame, preferably having a CTE that closely matches the CTE of the transparent sheet from block  902  and the CTE of the package base. In most cases where the base is alumina or Kovar alloy, a frame formed of Kovar alloy will be suitable. As previously described, the frame may be formed using, e.g., stamping, die-casting or other known metal-forming processes. The process then proceeds to block  912  as indicated by the arrow. 
     Block  912  represents the step of grinding, polishing and/or otherwise flattening the seal-ring areas of the frame as necessary to increase its flatness so that it will fit closely against the seal-ring areas of the transparent sheet. It will be appreciated that the steps represented by block  912  are optional and may not be necessary or present in every embodiment of the invention. The process then proceeds to block  914  as indicated by the arrow. 
     Block  914  represents the step of applying additional metallic layers to the seal-ring areas of the frame. These metallic layers are sometimes necessary to achieve compatible chemistry for bonding with the metallized seal-ring areas of the transparent sheet. In most embodiments, block  914  will represent numerous sub-steps for applying successive metallic layers to the frame. Block  914  further represents the optional steps of cleaning the frame (or at least the seal-ring area of the frame) to remove any greases, oils or other contaminants from the surface of the frame. As previously discussed, such cleaning steps may be performed regardless of whether the seal-ring area of the frame is to be metallized with additional metal layers or is to be used without additional metallization. Once the steps represented by block  914  are completed, the frame is ready for joining to the transparent sheet. Thus, the results of process block  908  and block  914  both proceed to block  916  as indicated by the arrows. 
     Block  916  represents the step of clamping the prepared frame together with the prepared transparent sheet so that their respective metallized seal-ring areas are in contact with one another under conditions producing a predetermined contact pressure at the junction region circumscribing the window portion. This predetermined contact pressure between the seal-ring surfaces allows thermal compression (TC) bonding of the metallized surfaces to occur at a lower temperature than would be required for conventional welding (including most soldering and brazing processes). The process then proceeds to block  918  as indicated by the arrow. 
     Block  918  represents the step of applying heat to the junction between the frame and the transparent sheet while maintaining the predetermined contact pressure until the temperature is sufficient to cause thermal compression bonding to occur. In some embodiments, block  918  will represent a single heating step, e.g., heating the fixtured assembly in a furnace. In other embodiments, block  918  will represent several sub-steps for applying heat to the junction area, for example, first preheating the fixtured assembly (e.g., in a furnace) to an intermediate temperature, and then using resistance welding techniques along the junction to raise the temperature of the localized area of the metallic layers the rest of the way to the temperature where thermal compression bonding will occur. The thermal compression bonding creates a hermetic seal between the transparent sheet material and the frame. The process then proceeds to block  920  as indicated by the arrow. 
     In the illustrated example, metallized seal-ring areas are joined using diffusion bonding/thermal compression bonding in which the predetermined pressure is applied first (block  916 ) and the heat is applied second (block  918 ). It will be appreciated, however, that the use of diffusion bonding is not limited to these specific conditions. In some other embodiments, the sheet and/or frame may not be metallized prior to bonding. In still other embodiments, the heat may be applied first until the desired bonding temperature is reached, and the predetermined pressure may be applied thereafter until the diffusion bond is formed. In yet additional embodiments, the heat and pressure may be applied simultaneously until the diffusion bond is formed. 
     Block  920  represents the step of completing the window assembly. Block  920  may represent merely cooling the window assembly after thermal compression bonding, or it may represent additional finishing processes including chamfering the edges of the assembly to prevent chipping, cracking, etc., marking the assembly, coating the window and/or the frame with one or more materials, or other post-assembly procedures. The process of this embodiment has thus been described. 
     It will be appreciated that in alternative embodiments of the invention, conventional welding techniques (including soldering and/or brazing) may be used instead of thermal compression bonding to join the frame to the transparent sheet. In such alternative embodiments, the steps represented by blocks  916  and  918  of  FIG. 9  would be replaced by the steps of fixturing the frame and transparent sheet together so that the metallized seal-ring areas are in contact with one another (but not necessarily producing a predetermined contact pressure along the junction) and then applying heat to the junction area using conventional means until the temperature is sufficient to cause the melting and diffusing of the metallic layers necessary to achieve the welded bond. 
     In an alternative embodiment, braze-soldering is used to join the frame  302  to the metallized sheet  304 . In this embodiment, a solder metal or solder alloy may be utilized as the final layer of the metallic layers  610  on the metallized sheet  304 , and clamping the sheet  304  to the frame  302  at a high predetermined contact pressure is not required. A solder metal or solder alloy preform may be utilized as a separate, intermediate item between the frame  302  and the sheet  304  instead of having a solder metal or solder alloy as the final layer of the metallic layers  610  on the metallized sheet  304 . Light to moderate clamping pressure can be used: 1) to insure alignment during the solder&#39;s molten phase; and 2) to promote even distribution of the molten solder all along the junction region between the respective seal-ring areas; thereby helping to insure a hermetic seal, however, this clamping pressure does not contribute to the bonding process itself as in TC bonding. In most other respects, however, this embodiment is substantially similar to that previously described. 
     The following examples, not to be considered limiting, are provided to illustrate the details of the metallic layers  610  in the sheet seal-ring area  318  that are suitable for braze-soldering to a Kovar alloy/nickel/gold frame  302  such as that illustrated in  FIG. 7 . 
     Example 33 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.002 
                 25 
               
               
                 2 
                 Cu 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Eutectic Au—Sn 
                 CVD, PVD, SBP 
                 1.27 
                 127 
               
               
                   
                 solder 
               
               
                   
               
            
           
         
       
     
     Example 34 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.002 
                 25 
               
               
                 2 
                 Cu 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Sn—Bi solder 
                 CVD, PVD, SBP 
                 1.27 
                 152.4 
               
               
                   
               
            
           
         
       
     
     Example 35 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.002 
                 25 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Eutectic Au—Sn 
                 CVD, PVD, SBP 
                 1.27 
                 127 
               
               
                   
                 solder 
               
               
                   
               
            
           
         
       
     
     Example 36 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.002 
                 25 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Sn—Bi solder 
                 CVD, PVD, SBP 
                 1.27 
                 152.4 
               
               
                   
               
            
           
         
       
     
     Example 37 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.002 
                 0.15 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Eutectic Au—Sn 
                 CVD, PVD, SBP 
                 1.27 
                 127 
               
               
                   
                 solder 
               
               
                   
               
            
           
         
       
     
     Example 38 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.002 
                 0.15 
               
               
                 2 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Eutectic Au—Sn 
                 CVD, PVD, SBP 
                 1.27 
                 127 
               
               
                   
                 solder 
               
               
                   
               
            
           
         
       
     
     Example 39 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.002 
                 0.15 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Sn—Bi solder 
                 CVD, PVD, SBP 
                 1.27 
                 152.4 
               
               
                   
               
            
           
         
       
     
     Example 40 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.002 
                 0.15 
               
               
                 2 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Sn—Bi solder 
                 CVD, PVD, SBP 
                 1.27 
                 152.4 
               
               
                   
               
            
           
         
       
     
     Example 41 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.002 
                 0.15 
               
               
                 2 
                 Sn—Bi solder 
                 CVD, PVD, SBP 
                 1.27 
                 152.4 
               
               
                   
               
            
           
         
       
     
     Example 42 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 De-stressed Sn 
                 CVD, PVD 
                 1.27 
                 152.4 
               
               
                   
                 Solder 
               
               
                   
               
            
           
         
       
     
     Example 43 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Sn—Bi Solder 
                 CVD, PVD 
                 1.27 
                 152.4 
               
               
                   
               
            
           
         
       
     
     Example 44 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Eutectic Au—Sn 
                 CVD, PVD 
                 1.27 
                 127 
               
               
                   
                 Solder 
               
               
                   
               
            
           
         
       
     
     Example 45 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.002 
                 152.4 
               
               
                 2 
                 Eutectic Au—Sn 
                 CVD, PVD, SBP 
                 1.27 
                 127 
               
               
                   
                 Solder 
               
               
                   
               
            
           
         
       
     
     Example 46 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.002 
                 152.4 
               
               
                 2 
                 Sn—Bi Solder 
                 CVD, PVD, SBP 
                 1.27 
                 152.4 
               
               
                   
               
            
           
         
       
     
     While numerous examples herein show the use of eutectic Au—Sn, other applications may utilize non-eutectic Au—Sn, or other eutectic or non-eutectic solders for attaching the window. This allows subsequent use of a higher melting temperature solder to attach the unit to a higher level assembly without melting the window bond. 
     By way of further examples, not to be considered limiting, the following combinations are preferred for the metallic layers  610  in the sheet seal-ring area  318  for braze-soldering to a Kovar alloy/nickel/gold frame  302  such as that illustrated in  FIG. 7 . 
     Example 47 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.1 
                 2.54 
               
               
                 2 
                 Cu 
                 CVD, PVD, SBP 
                 0.25 
                 2.54 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Eutectic Au—Sn 
                 CVD, PVD, SBP 
                 2.54 
                 63.5 
               
               
                   
                 solder 
               
               
                   
               
            
           
         
       
     
     Example 47a 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.1 
                 2.54 
               
               
                 2 
                 Cu 
                 CVD, PVD, SBP 
                 0.25 
                 2.54 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Sn—Cu—Ag Solder 
                 CVD, PVD, SBP 
                 2.54 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 48 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.1 
                 2.54 
               
               
                 2 
                 Cu 
                 CVD, PVD, SBP 
                 0.25 
                 2.54 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Sn—Bi solder 
                 CVD, PVD, SBP 
                 2.54 
                 127 
               
               
                   
               
            
           
         
       
     
     Example 49 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.1 
                 2.54 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.3175 
                 5.08 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Eutectic Au—Sn 
                 CVD, PVD, SBP 
                 2.54 
                 63.5 
               
               
                   
                 solder 
               
               
                   
               
            
           
         
       
     
     Example 49a 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.1 
                 2.54 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.3175 
                 5.08 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Sn—Cu—Ag Solder 
                 CVD, PVD, SBP 
                 2.54 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 50 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.1 
                 2.54 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.3175 
                 5.08 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Sn—Bi solder 
                 CVD, PVD, SBP 
                 2.54 
                 127 
               
               
                   
               
            
           
         
       
     
     Example 51 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.3175 
                 5.08 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Eutectic Au—Sn 
                 CVD, PVD, SBP 
                 2.54 
                 63.5 
               
               
                   
                 solder 
               
               
                   
               
            
           
         
       
     
     Example 51a 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.3175 
                 5.08 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Sn—Cu—Ag Solder 
                 CVD, PVD, SBP 
                 2.54 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 52 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                 2 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 3 
                 Eutectic Au—Sn 
                 CVD, PVD, SBP 
                 2.54 
                 63.5 
               
               
                   
                 solder 
               
               
                   
               
            
           
         
       
     
     Example 52a 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                 2 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 3 
                 Sn—Cu—Ag Solder 
                 CVD, PVD, SBP 
                 2.54 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 53 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.3175 
                 5.08 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Sn—Bi solder 
                 CVD, PVD, SBP 
                 2.54 
                 127 
               
               
                   
               
            
           
         
       
     
     Example 54 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                 2 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 3 
                 Sn—Bi solder 
                 CVD, PVD, SBP 
                 2.54 
                 127 
               
               
                   
               
            
           
         
       
     
     Example 55 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                 2 
                 Sn—Bi solder 
                 CVD, PVD, SBP 
                 2.54 
                 127 
               
               
                   
               
            
           
         
       
     
     Example 56 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 De-stressed Sn 
                 CVD, PVD 
                 2.54 
                 127 
               
               
                   
                 Solder 
               
               
                   
               
            
           
         
       
     
     Example 57 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Sn—Bi Solder 
                 CVD, PVD 
                 2.54 
                 127 
               
               
                   
               
            
           
         
       
     
     Example 58 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Eutectic Au—Sn 
                 CVD, PVD 
                 2.54 
                 63.5 
               
               
                   
                 Solder 
               
               
                   
               
            
           
         
       
     
     Example 58a 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Sn—Cu—Ag Solder 
                 CVD, PVD 
                 2.54 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 59 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.1 
                 5.08 
               
               
                 2 
                 Eutectic Au—Sn 
                 CVD, PVD, SBP 
                 2.54 
                 63.5 
               
               
                   
                 Solder 
               
               
                   
               
            
           
         
       
     
     Example 59a 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.1 
                 5.08 
               
               
                 2 
                 Sn—Cu—Ag Solder 
                 CVD, PVD, SBP 
                 2.54 
                 63.5 
               
               
                   
               
            
           
         
       
     
     Example 60 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.1 
                 5.08 
               
               
                 2 
                 Sn—Bi Solder 
                 CVD, PVD, SBP 
                 2.54 
                 127 
               
               
                   
               
            
           
         
       
     
     Referring now to  FIG. 10 , there is illustrated yet another embodiment of the current invention. Note that in this embodiment, the cover assembly  300  is circular in configuration rather than rectangular. It will be appreciated that this is simply another possible configuration for a cover assembly manufactured in accordance with this invention, and that this embodiment is not limited to configurations of any particular shape. As in the embodiment previously described, this embodiment also uses braze-soldering to hermetically join the transparent sheet  304  to the frame  302 . However, in this embodiment, the solder for braze soldering is provided in the form of a separate solder preform  1000  having the shape of the sheet seal-ring area  318  or the frame seal-ring area  310 . Also in this embodiment, preform  1000  can be of materials other than solder for use as an innerlayer or interlayer material between the transparent sheet  304  and the frame  302 . When used as the innerlayer or interlayer for TC bonding, one or more elements of preform  1000  diffuses with one or more elements of sheet  304  and the frame  302 . 
     In this embodiment, when the preform solder  1000  is used for braze-soldering to hermetically join the transparent sheet  304  to the frame  302 , instead of positioning the frame and the sheet directly against one another, the frame  302  and the sheet  304  are instead positioned against opposite sides of the solder preform  1000  such that the solder preform is interposed between the frame seal-ring area  310  and the sheet seal-ring are  318  along a continuous junction region that circumscribes the window portion  312 . After the frame  302  and sheet  304  are positioned against the solder preform  1000 , the junction region is heated until the solder preform fuses forming a solder joint between the frame and sheet all along the junction region. The heating of the junction region may be performed by any of the procedures previously described, including heating or preheating in a furnace, oven, etc., either alone or in combination with other heating methods including resistance welding. It is required that during the step of heating the junction region, the temperature of the window portion  312  of the sheet  304  remain below the glass transition temperature T G  and the softening temperature such that the finished surfaces  314  and  316  on the sheet are not adversely affected. 
     The current embodiment using a solder preform  1000  can be used for joining a metallized sheet  304  to a Kovar alloy/nickel/gold frame such as that illustrated in  FIG. 7 . In accordance with a preferred embodiment, the solder preform  1000  is formed of a gold-tin (Au—Sn) alloy, and in a more preferred embodiment, the gold-tin alloy is the eutectic composition. One of the alternative alloys for preform  1000  is tin-copper-silver (Sn—Cu—Ag). The thickness of the gold-tin preform  1000  will probably be within the range from about 6 microns to about 101.2 microns. The thickness of other alloys for preform  1000  will also probably be within the range of about 6 microns to about 101.2 microns. 
     The following examples, not to be considered limiting, are provided to illustrate the details of the metallic layers  610  and the sheet seal-ring area  318  that are suitable for braze-soldering to a Kovar alloy/nickel/gold frame in combination with a gold-tin solder preform or other suitable solder alloy preforms, including, but not limited to tin-copper-silver alloys. 
     Example 61 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.002 
                 25 
               
               
                 2 
                 Cu 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Au 
                 CVD, PVD, SBP 
                 0.0508 
                 0.508 
               
               
                   
               
            
           
         
       
     
     Example 62 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.002 
                 25 
               
               
                 2 
                 Cu 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Sn—Bi 
                 CVD, PVD, SBP 
                 0.635 
                 12.7 
               
               
                   
               
            
           
         
       
     
     Example 63 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.002 
                 25 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Au 
                 CVD, PVD, SBP 
                 0.0508 
                 0.508 
               
               
                   
               
            
           
         
       
     
     Example 64 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.002 
                 25 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Sn—Bi 
                 CVD, PVD, SBP 
                 0.635 
                 12.7 
               
               
                   
               
            
           
         
       
     
     Example 65 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.002 
                 0.15 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Au 
                 CVD, PVD, SBP 
                 0.0508 
                 0.508 
               
               
                   
               
            
           
         
       
     
     Example 66 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.002 
                 0.15 
               
               
                 2 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Au 
                 CVD, PVD, SBP 
                 0.0508 
                 0.508 
               
               
                   
               
            
           
         
       
     
     Example 67 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.002 
                 0.15 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 4 
                 Sn—Bi 
                 CVD, PVD, SBP 
                 0.635 
                 12.7 
               
               
                   
               
            
           
         
       
     
     Example 68 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.002 
                 0.15 
               
               
                 2 
                 Ni 
                 CVD, PVD, SBP 
                 0.002 
                 6.35 
               
               
                 3 
                 Sn—Bi 
                 CVD, PVD, SBP 
                 0.635 
                 12.7 
               
               
                   
               
            
           
         
       
     
     Example 69 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.002 
                 0.15 
               
               
                 2 
                 Sn—Bi 
                 CVD, PVD, SBP 
                 0.635 
                 12.7 
               
               
                   
               
            
           
         
       
     
     Example 70 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.002 
                 0.15 
               
               
                   
               
            
           
         
       
     
     Example 71 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 De-stressed Sn 
                 CVD, PVD 
                 0.635 
                 12.7 
               
               
                   
                 or Sn—Bi 
               
               
                   
               
            
           
         
       
     
     Example 72 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Au 
                 CVD, PVD 
                 0.0508 
                 0.508 
               
               
                   
               
            
           
         
       
     
     Example 73 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.002 
                 152.4 
               
               
                 2 
                 Au 
                 CVD, PVD, SBP 
                 0.0508 
                 0.508 
               
               
                   
               
            
           
         
       
     
     Example 74 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.002 
                 152.4 
               
               
                 2 
                 Sn—Bi 
                 CVD, PVD, SBP 
                 0.635 
                 12.7 
               
               
                   
               
            
           
         
       
     
     Example 75 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.002 
                 152.4 
               
               
                 2 
                 Sn (De-stressed 
                 CVD, PVD, SBP 
                 0.635 
                 12.7 
               
               
                   
                 after deposition) 
               
               
                   
               
            
           
         
       
     
     By way of further examples, not to be considered limiting, the following combinations are preferred for the metallic layers  610  and the sheet seal-ring area  318  for braze-soldering to a Kovar alloy/nickel/gold frame in combination with a gold-tin soldered preform. In addition to having a frame of Kovar alloy/nickel/gold, materials other than Kovar may be employed as the frame&#39;s base material and the overlying layer or layers may be nickel without the gold, or combinations of two or more metals including, but not limited to nickel and gold. 
     Example 76 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.1 
                 2.54 
               
               
                 2 
                 Cu 
                 CVD, PVD, SBP 
                 0.25 
                 2.54 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Au 
                 CVD, PVD, SBP 
                 0.127 
                 0.381 
               
               
                   
               
            
           
         
       
     
     Example 77 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.1 
                 2.54 
               
               
                 2 
                 Cu 
                 CVD, PVD, SBP 
                 0.25 
                 2.54 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Sn—Bi 
                 CVD, PVD, SBP 
                 2.54 
                 7.62 
               
               
                   
               
            
           
         
       
     
     Example 78 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.1 
                 2.54 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.3175 
                 5.08 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Au 
                 CVD, PVD, SBP 
                 0.127 
                 0.381 
               
               
                   
               
            
           
         
       
     
     Example 79 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 CVD, PVD 
                 0.1 
                 2.54 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.3175 
                 5.08 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Sn—Bi 
                 CVD, PVD, SBP 
                 2.54 
                 7.62 
               
               
                   
               
            
           
         
       
     
     Example 80 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.3175 
                 5.08 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Au 
                 CVD, PVD, SBP 
                 0.127 
                 0.381 
               
               
                   
               
            
           
         
       
     
     Example 81 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                 2 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 3 
                 Au 
                 CVD, PVD, SBP 
                 0.127 
                 0.381 
               
               
                   
               
            
           
         
       
     
     Example 82 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                 2 
                 Zn 
                 CVD, PVD, SBP 
                 0.3175 
                 5.08 
               
               
                 3 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 4 
                 Sn—Bi 
                 CVD, PVD, SBP 
                 2.54 
                 7.62 
               
               
                   
               
            
           
         
       
     
     Example 83 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                 2 
                 Ni 
                 CVD, PVD, SBP 
                 1 
                 5.08 
               
               
                 3 
                 Sn—Bi 
                 CVD, PVD, SBP 
                 2.54 
                 7.62 
               
               
                   
               
            
           
         
       
     
     Example 84 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                 2 
                 Sn—Bi 
                 CVD, PVD, SBP 
                 2.54 
                 7.62 
               
               
                   
               
            
           
         
       
     
     Example 85 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Cr 
                 CVD, PVD 
                 0.05 
                 0.12 
               
               
                   
               
            
           
         
       
     
     Example 86 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 De-stressed Sn 
                 CVD, PVD 
                 2.54 
                 7.62 
               
               
                   
                 or Sn—Bi 
               
               
                   
               
            
           
         
       
     
     Example 87 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Au 
                 CVD, PVD 
                 0.127 
                 0.381 
               
               
                   
               
            
           
         
       
     
     Example 88 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.1 
                 5.08 
               
               
                 2 
                 Au 
                 CVD, PVD, SBP 
                 0.127 
                 0.381 
               
               
                   
               
            
           
         
       
     
     Example 89 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.1 
                 5.08 
               
               
                 2 
                 Sn—Bi 
                 CVD, PVD, SBP 
                 2.54 
                 7.62 
               
               
                   
               
            
           
         
       
     
     Example 90 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 CVD, PVD 
                 0.1 
                 5.08 
               
               
                 2 
                 Sn (De-stressed 
                 CVD, PVD, SBP 
                 2.54 
                 7.62 
               
               
                   
                 after deposition) 
               
               
                   
               
            
           
         
       
     
     Referring now to  FIG. 11 , there is illustrated yet another embodiment of the current invention. This embodiment also uses soldering, however, in this embodiment the solder is applied via inkjet technology to either the metallized area  610  in the sheet seal-ring area  318  or the sheet seal-ring  310  of the frame assembly.  FIG. 11  shows a portion of the Kovar alloy/nickel/gold frame  302  (or other frame alloy and overlayer combination) and an inkjet dispensing head  1102  which is dispensing overlapping drops of solder  1104  onto the frame seal-ring area  310  as the dispensing head moves around the frame aperture  308  or the frame aperture is moved underneath the dispensing head, as indicated by arrow  1106 . Preferably, the inkjet dispensed solder is a gold-tin (Au—Sn) alloy, and more preferably it is the eutectic composition. The preferred thickness of the gold-tin solder applied by dispensing head  1102  in this embodiment is within the range from about 6 microns to about 101.2 microns. It will be appreciated that while the example illustrated in  FIG. 11  shows the dispensing head  1102  depositing the solder droplets  1104  onto the frame  302 , in other embodiments the inkjet deposited solder may be applied to the sheet seal-ring area  318 , either alone or in combination with applications on the frame seal-ring area  310 . In still other embodiments, the inkjet deposited solder may be used to create a discrete solder preform that would be employed as described in the previous examples herein. In still other embodiments, the inkjet deposited material, which may or may not be solder, may be used to create an innerlayer or interlay preform that would be employed for use in TC bonding or HIP diffusion bonding as described in previous examples herein. Details of the metallic layers  610  in the sheet seal-ring area  318  that are suitable for a soldering to a Kovar alloy/nickel/gold frame  302  such as that illustrated in  FIG. 7  using inkjet supplied solder are substantially identical to those layers illustrated in previous Examples 21 through 32. 
     Referring now to  FIGS. 12   a  through  12   c  and  FIGS. 13   a  through  13   c , there is illustrated yet another alternative method for manufacturing cover assemblies constituting another embodiment of the current invention. Whereas, in the previous embodiments a separate prefabricated metal frame was joined to the transparent sheet to act as a heat spreader/heat sink needed for subsequent welding, in this embodiment a cold gas dynamic spray deposition process is used to fabricate a metallic frame/heat spreader directly on the transparent sheet material. In other words, in this embodiment the frame is fabricated directly on the transparent sheet as an integral part, no subsequent joining operation is required. In addition, since cold gas dynamic spray deposition can be accomplished at near room temperature, this method is especially useful where the transparent sheet material and/or surface treatments thereto have a relatively low T G , melting temperature, or other heat tolerance parameter. 
     Referring specifically to  FIG. 12   a , there is illustrated a sheet of transparent material  304  having a window portion  312  defined thereupon. The window portion  312  has finished top and bottom surfaces  314  and  316  (note that the  304  sheet appears bottom side up in  FIGS. 12   a  through  12   c ). A frame attachment area  1200  is defined on the sheet  304 , the frame attachment area circumscribing the window portion  312 . It will be appreciated in the embodiment illustrated in  FIGS. 12   a - c  that the frame attachment area  1200  need not follow the specific boundaries of the window area  312  (i.e., which in this case are circular) as long as the frame attachment area  1200  completely circumscribes the window portion. 
     It will be appreciated that, unless specifically noted otherwise, the initial steps of obtaining a transparent sheet having a window portion with finished top and bottom surfaces, preparing the seal-ring area of the sheet and metallizing the seal-ring area of the sheet are substantially identical to those described for the previous embodiments and will not be described in detail again. 
     Referring now also to  FIG. 13   a , there is illustrated a partial cross-sectional view to the edge of the sheet  304 . In this example, the step of preparing a frame attachment area  1200  on the sheet  304  comprises an optional step of roughening the frame attachment area by roughening and/or grinding the surface from its original level (shown in broken line) to produce a recessed area  1302 . After the frame attachment area  1200  has been prepared, metal layers are deposited into the frame attachment area of the sheet using cold gas dynamic spray deposition. In  FIG. 12   b , an initial metal layer  1202  has been applied into the frame attachment area  1200  using cold gas dynamic spray deposition. 
     Referring now also to  FIG. 13   b , the cold gas dynamic spray nozzle  1304  is shown depositing a stream of metal particles  1306  onto the frame attachment area  1200 . The initial layer  1202  has now been overlaid with a secondary layer  1204  and the spray nozzle  1304  is shown as it begins to deposit the final Kovar alloy layer  1206 . Layer  1206  need not be Kovar. 
     Referring now to  FIGS. 12   c  and  13   c , the completed cover assembly  1210  is illustrated including the integral frame/heat spreader  1212 , which has been built up from layer  1206  to a predetermined height, denoted by reference numeral  1308 , above the finished surface of the sheet. In a preferred embodiment, the predetermined height  1308  of the built-up metal frame above the frame attachment area  1200  is within the range from about 5% to about 100% of the thickness denoted by reference numeral  1310  of the sheet  304  beneath the frame attachment area. In the embodiment shown, the step of depositing metal using cold gas dynamic spray included depositing a layer of Kovar alloy onto the sheet to fabricate the built-up frame/heat spreader  1212 . The use of cold gas dynamic spray deposition allows a tremendous range of thickness for this Kovar alloy layer, which thickness may be within the range from about 2.54 microns to about 12,700 microns. It will, of course, be appreciated that the frame/heat spreader  1212  may be fabricated through the deposition of materials other than Kovar alloy, depending upon the characteristics of the transparent sheet  304  and of the package base  104 , especially their respective CTEs. 
     The following examples, not to be considered limiting, are provided to illustrate the details of the metallic layers, denoted collectively by reference numeral  1207  for forming a frame/heat spreader compatible with hard glass transparent sheets and Kovar alloy or ceramic package bases. The deposition of materials other than Kovar alloy may be used as the final layer whenever Kovar Alloy is indicated as the final layer, depending upon the characteristics of the transparent sheet  304  and of the package base  104 , especially their respective CTEs. 
     Example 91 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 2 
                 Cu 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 3 
                 Ni 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 4 
                 Kovar Alloy 
                 cold gas spray 
                 127 
                 12,700 
               
               
                   
               
            
           
         
       
     
     Example 92 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 2 
                 Ni 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 3 
                 Kovar Alloy 
                 cold gas spray 
                 127 
                 12,700 
               
               
                   
               
            
           
         
       
     
     Example 93 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 2 
                 Kovar Alloy 
                 cold gas spray 
                 127 
                 12,700 
               
               
                   
               
            
           
         
       
     
     Example 94 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Kovar Alloy 
                 cold gas spray 
                 127 
                 12,700 
               
               
                   
               
            
           
         
       
     
     Example 95 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Zn 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 2 
                 Ni 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 3 
                 Kovar alloy 
                 cold gas spray 
                 127 
                 12,700 
               
               
                   
               
            
           
         
       
     
     Example 96 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Zn 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 2 
                 Kovar alloy 
                 cold gas spray 
                 127 
                 12,700 
               
               
                   
               
            
           
         
       
     
     Example 97 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 2 
                 Ni 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 3 
                 Kovar alloy 
                 cold gas spray 
                 127 
                 12,700 
               
               
                   
               
            
           
         
       
     
     Example 98 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 2 
                 Kovar alloy 
                 cold gas spray 
                 127 
                 12,700 
               
               
                   
               
            
           
         
       
     
     Example 99 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 A1 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 2 
                 Zn 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 3 
                 Ni 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 4 
                 Kovar Alloy 
                 cold gas spray 
                 127 
                 12,700 
               
               
                   
               
            
           
         
       
     
     Example 100 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 2 
                 Kovar Alloy 
                 cold gas spray 
                 127 
                 12,700 
               
               
                   
               
            
           
         
       
     
     Example 101 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Sn or Sn—Bi 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 2 
                 Zn 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 3 
                 Ni 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 4 
                 Kovar Alloy 
                 cold gas spray 
                 127 
                 12,700 
               
               
                   
               
            
           
         
       
     
     Example 102 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Sn or Sn—Bi 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 2 
                 Ni 
                 cold gas spray 
                 2.54 
                 127 
               
               
                 3 
                 Kovar Alloy 
                 cold gas spray 
                 127 
                 12,700 
               
               
                   
               
            
           
         
       
     
     By way of further examples, not to be considered limiting, the following combinations are preferred for the metallic layers  1207  for forming a frame/heat spreader compatible with hard glass transparent sheets and Kovar or other alloys or ceramic package bases. The deposition of materials other than Kovar alloy may be used as the final layer whenever Kovar Alloy is indicated as the final layer, depending upon the characteristics of the transparent sheet  304  and of the package base  104 , especially their respective CTEs. 
     Example 103 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 2 
                 Cu 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 3 
                 Ni 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 4 
                 Kovar Alloy 
                 cold gas spray 
                 635 
                 2,540 
               
               
                   
               
            
           
         
       
     
     Example 104 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 2 
                 Ni 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 3 
                 Kovar Alloy 
                 cold gas spray 
                 635 
                 2,540 
               
               
                   
               
            
           
         
       
     
     Example 105 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Al 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 2 
                 Kovar Alloy 
                 cold gas spray 
                 635 
                 2,540 
               
               
                   
               
            
           
         
       
     
     Example 106 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                 1 
                 Kovar Alloy 
                 cold gas spray 
                 635 
                 2,540 
               
               
                   
               
            
           
         
       
     
     Example 107 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Zn 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 2 
                 Ni 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 3 
                 Kovar alloy 
                 cold gas spray 
                 635 
                 2,540 
               
               
                   
               
            
           
         
       
     
     Example 108 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Zn 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 2 
                 Kovar alloy 
                 cold gas spray 
                 635 
                 2,540 
               
               
                   
               
            
           
         
       
     
     Example 109 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 2 
                 Ni 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 3 
                 Kovar alloy 
                 cold gas spray 
                 635 
                 2,540 
               
               
                   
               
            
           
         
       
     
     Example 110 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Cr 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 2 
                 Kovar alloy 
                 cold gas spray 
                 635 
                 2,540 
               
               
                   
               
            
           
         
       
     
     Example 111 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 A1 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 2 
                 Zn 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 3 
                 Ni 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 4 
                 Kovar Alloy 
                 cold gas spray 
                 635 
                 2,540 
               
               
                   
               
            
           
         
       
     
     Example 112 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Ni 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 2 
                 Kovar Alloy 
                 cold gas spray 
                 635 
                 2,540 
               
               
                   
               
            
           
         
       
     
     Example 111 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Sn or Sn—Bi 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 2 
                 Zn 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 3 
                 Ni 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 4 
                 Kovar Alloy 
                 cold gas spray 
                 635 
                 2,540 
               
               
                   
               
            
           
         
       
     
     Example 114 
       
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Min. 
                 Max. 
               
               
                 Layers 
                 Metal 
                 Deposition 
                 (microns) 
                 (microns) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 Sn or Sn—Bi 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 2 
                 Ni 
                 cold gas spray 
                 12.7 
                 76.2 
               
               
                 3 
                 Kovar Alloy 
                 cold gas spray 
                 635 
                 2,540 
               
               
                   
               
            
           
         
       
     
     After the deposition of the metal layers using the cold gas dynamic spray deposition, it may be necessary to grind or shape the top surface of the built-up frame  1212  to a predetermined flatness before performing additional steps to ensure that a good contact will be made in later bonding. Another process which may be used, either alone or in combination with shaping the top surface of the built-up frame, is the depositing of additional metal layers onto the built-up frame/heat spreader  1212  using solution bath plating. The most common reason for such plated layers is to promote a good bonding when the frame/heat spreader is adjoined to the package base  104 . In a preferred embodiment, the additional metallic layers applied to the built-up frame  1212  include a layer of nickel directly over the cold gas dynamic spray deposited metal having a thickness within the range of about 0.002 microns to about 25 microns and, in some instances, then solution bath plating a layer of gold over the nickel layer until the gold layer has a thickness within the range from about 0.0508 microns to about 0.508 microns. 
     Referring now to  FIG. 14 , there is illustrated a block diagram of the alternative embodiment utilizing cold gas dynamic spray deposition. It will be appreciated that, unless specifically noted otherwise, the initial steps of obtaining a transparent sheet having finished surfaces, applying surface treatments to the sheet, cleaning, roughening or otherwise preparing the frame attachment area of the sheet are substantially identical to those described for the previous embodiments and will not be described in detail again. For example, block  1402  of  FIG. 14  represents the step of obtaining a sheet of transparent material having finished surfaces and corresponds directly with block  902 , and with the description of suitable transparent materials. Similarly, except as noted, blocks  1404 ,  1406  and  1408  of  FIG. 14  correspond directly with blocks  904 ,  906  and  908 , respectively, of  FIG. 9  and with the previous descriptions of the steps and sub-steps provided herein. Thus, it will be understood that all of the options described for performing the various steps and sub-steps represented by the blocks  902 - 908  in the previous (i.e., prefabricated frame) embodiments are applicable to the blocks  1402 - 1408  in the current (i.e., cold spray) embodiment. 
     The next step of the process is to use cold gas dynamic spray deposition to deposit frame/heat spreader metal onto any previously deposited metal layers in the frame attachment area  1200 . This step is represented by block  1410 . As previously described in connection with  FIGS. 13   b  and  13   c , the high velocity particles  1306  from the gas nozzle  1304  form a new layer on the previous metallic layers, and by directing the cold spray jet across the frame attachment area  1200  repeatedly, the new material can become a continuous metallic layer around the entire periphery of the frame attachment area, i.e., it will circumscribe the window portion  312  of the transparent sheet  304 . Where the material of the package base  104  (to which the cover assembly  1210  will eventually be joined) is Kovar alloy or appropriately metallized alumina, Kovar alloy is preferred for the material  1206  to be cold sprayed to form the integral frame. In other cases, a heat spreader material should be selected which has a CTE that is closely matched to the CTE of the package base  104 . Of course, that material must also be compatible with the cold gas dynamic spray process. 
     The cold spraying of the powdered heat spreader material is continued until the new layer  1206  reaches the thickness required to serve as a heat spreader/integral frame. This would represent the end of the process represented by block  1410 . For some applications, the built-up heat spreader/frame  1212  is now complete and ready for use. For other applications, however, performing further finishing operations on the heat spreader/frame  1212  may be desirable. 
     For example, it is known that significant residual stresses may be encountered in metal structures deposited using cold-gas dynamic spray technology as a result of the mechanics of the spray process. These stresses may make the resulting structure prone to dimensional changes, cracking or other stress-related problems during later use. Annealing by controlled heating and cooling is known to reduce or eliminate residual stresses. Thus, in some applications, the integral heat spreader/frame  1212  is annealed following its deposition on the sheet  304 . This optional step is represented by block  1411  in  FIG. 14 . In some embodiments, the annealing step  1411  may include the annealing of the totality of the sprayed-on metals and alloys constituting the heat spreader/frame  1212 . In other embodiments, however, the annealing step  1411  includes annealing only the outermost portions of the integral built-up heat spreader/frame  1212 , while the inner layers are left unannealed. 
     It will be appreciated that there are flatness requirements for the sealing surface at the “top” of the heat spreader (which is actually projecting from the bottom surface  316  of the sheet). If these flatness requirements are not met via the application of the heat spreader material by the cold spray process, it will be necessary to flatten the sealing surface at the next step of the process. This step is represented by block  1412  in  FIG. 14 . There are a number of options for achieving the required surface flatness. First, it is possible to remove surface material from the heat spreader to achieve the required flatness. This may be accomplished by conventional surface grinding, by other traditional mechanical means, or it may be accomplished by the laser removal of high spots. Where material removal is used, care must be taken to avoid damaging the finished window surfaces  314  and  316  during the material removal operations. Special fixturing and/or masking of the window portion  312  may be required. Alternatively, if the cold spray deposited heat spreader  1212  is ductile enough, the surface may be flattened using a press operation, i.e., pressing the frame against a flat pattern or by employing a rolling operation. This would reduce the handling precautions as compared to using a surface grinder or laser operations. 
     Finally, as previously described, in some embodiments additional metal layers are plated onto the integral frame/heat spreader  1212 . These optional plating operations, such as solution bath plating layers of nickel and gold onto a Kovar alloy frame, are represented by block  1414  in  FIG. 14 . In the embodiment shown in  FIG. 14 , the optional plating operation  1414  is performed after the optional flattening operation  1412 , which in turn is performed after the optional annealing operation  1411 . While such order is preferred, it will be appreciated that in other embodiments the order of the optional finishing steps  1411 ,  1412  and  1414  may be rearranged. The primary considerations for the ordering of these finishing steps is whether later steps will damage the results of earlier steps. For example, it would be impractical to perform plating step  1414  before the flattening step  1412  if the flattening was to be carried out by grinding, while it might be acceptable if the flattening was to be carried out by pressing. 
     Referring now to  FIGS. 15   a  and  15   b , there is illustrated a method for manufacturing multiple cover assemblies simultaneously in accordance with another embodiment of the current invention. Shown in  FIG. 15   a  is an exploded view of a multi-unit assembly, which can be subdivided after fabrication to produce individual cover assemblies. The multi-unit assembly  1500  includes a frame  1502  and a sheet  1504  of a transparent material. The frame  1502  has sidewalls  1506  defining a plurality of frame apertures  1508  therethrough. Each frame aperture  1508  is circumscribed by a continuous sidewall section having a frame seal-ring area  1510  (denoted by cross-hatching). Each frame seal-ring area  1510  has a metallic surface, which may result from the inherent material of the frame  1502  or it may result from metal layers, which have been applied to the surface of the frame. In some embodiments, the frame  1502  includes reduced cross-sectional thickness areas  1509  formed on the frame sidewalls  1506  between adjacent frame apertures  1508 .  FIG. 15   b  shows the bottom side of the frame  1502 , to better illustrate the reduced cross-sectional thickness areas  1509  formed between each aperture  1508 . Also illustrated is the base seal-ring area  1520  (denoted by cross-hatching) which surrounds each aperture  1508  to allow joining to the package bases  104 . 
     Further regarding the multi-aperture frames illustrated in  FIGS. 15   a  and  15   b , it will be understood that the frame  1502  can be attached as shown, with the open ends of the V-shaped notches facing away from the sheet, or alternatively, with the open ends of the V-shaped notches facing toward the sheet. 
     Except for the details just described, the multiple-aperture frame  1502  of this embodiment shares material, fabrication and design details with the single aperture frame  302  previously described. In this regard, a preferred embodiment of the frame  1502  is primarily formed of Kovar alloy or similar materials and more preferably, will have a Kovar alloy core with a surface layer of gold overlaying an intermediate layer of nickel as previously described. 
     The transparent sheet  1504  for the multi-unit assembly can be formed from any type of transparent material as previously discussed for sheet  304 . In this embodiment, however, the sheet  1504  has a plurality of window portions  1512  defined thereupon, with each window portion having finished top and bottom surface  1514  and  1516 , respectively. A plurality of sheet seal-ring areas  1518  are denoted by cross-hatching surrounding each window portion in  FIG. 15   a . With respect to the material of the sheet  1504 , with respect to the finished configuration of the top and bottom surfaces  1514  and  1516 , respectively, of each window portion  1512 , with respect to surface treatments, and/or coatings, the sheet  1504  is substantially identical to the single window portion sheet  304  previously discussed. 
     The next step of the process of manufacturing the multi-unit assembly  1500  is to prepare the sheet seal-ring areas  1518  for metallization. As noted earlier, each sheet seal-ring area  1518  circumscribes a window portion of the sheet  1504 . The sheet seal-ring areas  1518  typically have a configuration which closely matches the configuration of the frame seal-ring areas  1510  to which they will eventually be joined. It will be appreciated, however, that in some cases other considerations will affect the configuration of the frame grid, e.g., when electrical resistance heating is used to produce bonding, then the seal-ring areas  1518  must be connected to form the appropriate circuits. The steps of preparing the sheet seal-ring areas  1518  for metallization is substantially identical to the steps and options presented during discussion of preparing the frame seal-ring area  310  on the single aperture frame  302 . Thus, at a minimum, preparing the sheet seal-ring area  1518  typically involves a thorough (e.g., plasma, solvent or detergent) cleaning to remove any contaminants from the surfaces and typically also involves roughening the seal-ring area by chemical etching, laser ablating, mechanical grinding or sandblasting this area. 
     The step of metallizing the prepared sheet seal-ring areas  1510  of the sheet  1502  are substantially identical to the steps described for metallizing the frame seal-ring area  310  on the single aperture frame  302 . For example, the metal layers shown in Examples 1 through 120 can be used in connection with thermal compression bonding, for soldering where the solder material is plated onto the sheet as a final metallic layer, and can be used in connection with soldering in combination with a separate gold-tin of solder preform and also for soldering in connection with solders deposited or formed using inkjet technology. 
     The next step of the process is to position the frame  1502  against the sheet  1504  (it being understood that solder preforms or solder layers would be interposed between the frame and the sheet if braze soldering is used to join the frame  1502  to the sheet  1504 ) such that each of the window portions  1512  overlays one of the frame apertures  1508 , and that for each such window portion/frame aperture combination, at least a portion of the associated frame seal-ring area  1510  and at least a portion of the associated sheet seal-ring area  1518  contact one another along a continuous junction region that circumscribes the associated window portion. This operation is generally analogous to the steps of positioning the frame against the sheet in the single aperture embodiment previously described. If diffusion bonding is used to join the frame  1502  to the sheet  1504 , an interlayer or innerlayer between the frame  1502  to the sheet  1504  may or may not be employed. 
     Referring now to  FIG. 16   a , there is illustrated the positioning of a multi-window sheet  1504  (in this case having window portions  1512  with contoured surfaces) against a multi-aperture frame  1502  using compliant tooling in accordance with another embodiment. The compliant tooling includes a compliant element  1650  and upper and lower support plates  1652 ,  1654 , respectively. The support plates  1652  and  1654  receive compressive force, denoted by arrows  1656 , at discrete locations from tooling fixtures (not shown). The compliant member  1650  is positioned between one of the support plates and the cover assembly pre-fab (i.e., frame  1502  and sheet  1504 ). The compliant member  1650  yields elastically when a force is applied, and therefore can conform to irregular surfaces (such as the sheet  1504 ) while at the same time applying a distributed force against the irregular surface to insure that the required contact pressure is achieved all along the frame/sheet junction. Such compliant tooling can also be used to press a sheet or frame against the other member when the two members are not completely flat, taking advantage of the inherent flexibility (even if small) present in all materials. In the illustrated example, the compliant member  1650  is formed from a solid block of an elastomer material, e.g., rubber, however in other embodiments the compliant member may also be fabricated from discrete elements, e.g., springs. The compliant material must be able to withstand the elevated temperatures experienced during the bonding operation. 
     The next step of the process is heating all of the junction regions until a metal-to-metal joint is formed between the frame  1502  and the sheet  1504  all along each junction region, thus creating the multi-unit assembly  1500  having a hermetic frame/sheet seal circumscribing each window portion  1512 . If diffusion bonding is used to join the frame  1502  and the sheet  1504 , the bond could be between the outermost metal layer of the frame and the non-metallized sheet  1504 . It will be appreciated that any of the heating technologies previously described for joining the single aperture frame  302  to the single sheet  304  are applicable to joining the multi-aperture frame  1502  to the corresponding multi-window sheet  1504 . 
     Referring now to  FIG. 16   b , the final step of the current process is to divide the multi-unit assembly  1500  along each junction region that is common between two window portions  1512  taking care to preserve and maintain the hermetic seal circumscribing each window portion. A plurality of individual cover assemblies are thereby produced.  FIG. 16   b , illustrates a side view of a multi-unit assembly  1500  following the hermetic bonding of the sheet  1504  to the frame  1502 . Where the frame  1502  includes reduced cross-sectional thickness areas  1509 , the step of dividing the multi-unit assembly may include scoring the frame along the back side of the reduced cross-sectional thickness area at the position indicated by arrow  1602 , preferably breaking through or substantially weakening the remaining frame material below area  1509 , and also simultaneously scoring the sheet  1504  along a line vertically adjacent to area  1509 , i.e., at the point indicated by arrow  1604 , followed by flexing the assembly  1500 , e.g., in the direction indicated by arrows  1606  such that a fracture will propagate away from the score along line  1608 , thereby separating the assembly into two pieces. This procedure can be repeated along each area of reduced cross-sectional thickness  1509  until the multi-unit assembly  1500  has been completely subdivided into single aperture cover assemblies that are substantially identical to those produced by the earlier method described herein. In other embodiments, instead of using the score-and-break method, the cover assemblies may be cut apart, preferably from the frame side along the path indicated by arrow  1602  (i.e., between the window portions  1512 ), using mechanical cutting, dicing wheel, laser, water jet or other parting technology. 
     Referring now to  FIGS. 17   a  and  17   b , there is illustrated yet another method for simultaneously manufacturing multiple cover assemblies. This method expands upon the cold gas dynamic spray technique used to build an integral frame/heat spreader directly upon the transparent sheet material as previously illustrated in connection with  FIGS. 12   a  through  12   c  and  FIGS. 13   a  through  13   c . As shown in  FIG. 17   a , the process starts with a sheet of nonmetallic transparent material  1704  having a plurality of window portions  1712  defined thereupon, each window portion having finished top and bottom surfaces  1714  and  1716 , respectively. The properties and characteristics of the transparent sheet  1704  are identical to those in the embodiments previously discussed. The next step of the process involves preparing a plurality of frame attachment areas  1720  (denoted by the path of the broken line surrounding each window portion  1712 ), each frame attachment area  1720  circumscribing one of the window portions  1712 . As in previous embodiments, the step of preparing the frame attachment areas may comprise cleaning, roughening, grinding or otherwise modifying the frame attachment areas in preparation for metallization. 
     The next step in this process is metallizing the prepared frame attachment areas on the sheet, i.e., this metallization may be performed using a cold gas dynamic spray technology or where the layers are relatively thin, using a CVD, physical vapor deposition or other conventional metal deposition techniques. It will be appreciated that the primary purpose of this step is to apply metal layers necessary to obtain good adhesion to the transparent sheet  1704  and/or to meet the metallurgical requirements for corrosion prevention, etc. 
     Referring now to  FIG. 17   b , the next step of the process is depositing metal onto the prepared/metallized frame attachment areas of the sheet  1704  using cold gas dynamic spray deposition techniques until a built-up metal frame  1722  is formed upon the sheet having a seal-ring area  1726  that is a predetermined vertical thickness above the frame attachment areas, thus creating a multi-unit assembly having an inherent hermetic seal between the frame  1722  and the sheet  1704  circumscribing each window portion  1712 . In some embodiments, reduced cross-sectional thickness areas  1724  are formed by selectively depositing the metal during the cold spray deposition. In other embodiments, the reduced cross-sectional area sections  1724  may be formed following deposition of the frame/heat spreader  1722  through the use of grinding, cutting or other mechanical techniques such as laser ablation and water jet. In addition, the reduced cross-sectional area sections  1724  may be formed following deposition of the frame/heat spreader  1722  through the use of photo-chemical machining (PCM). 
     The next step of the process which, while not required is strongly preferred, is to flatten, if necessary, the seal-ring area  1726  of the sprayed-on frame  1722  to meet the flatness requirements for joining it to the package base  104 . This flattening can be accomplished by mechanical means, e.g., grinding, lapping, polishing, etc., or by other techniques such as laser ablation. 
     The next step of the process, which, while not required, is strongly preferred, is to add additional metallic layers, e.g., a nickel layer and preferably also a gold layer, to the seal-ring area  1726  of the sprayed-on frame  1722  to facilitate welding the cover assembly to the package base  104 . These metallic layers are preferably added using a solution bath plating process, e.g., solution bath plating, although other techniques may be used. 
     The next step of the process is dividing the multi-unit assembly  1700  along each frame wall section common between two window portions  1712  while, at the same time, preserving and maintaining the hermetic seal circumscribing each window portion. After dividing the multi-unit  1700 , a plurality of single aperture cover assemblies  1728  (shown in broken line) will be produced, each one being substantially identical to the single aperture cover assemblies produced using the method described in  FIGS. 12   a  through  12   c  and  FIGS. 13   a  through  13   c . All of the options, characteristics and techniques described for use in the single unit cover assembly produced using cold gas dynamic spray technology are applicable to this embodiment. It will be appreciated that certain operations for example, the flattening of the frame and the plating of the frame with additional metallic layers, may be performed on the multi-unit assembly  1700 , prior to separation of the individual units, or on the individual units after separation. 
     As previously described, heating the junction region between the metallized seal-ring area of the transparent sheet and the seal-ring area of the frame is required for forming the hermetic seal therebetween. Also as previously described, this heating may be accomplished using a furnace, oven, or various electrical heating techniques, including electrical resistance heating (ERH). Referring now to  FIGS. 18   a - 18   c , there is illustrated methods of utilizing electric resistance heating to manufacture multiple cover assemblies simultaneously. 
     Referring first to  FIG. 18   a , there is illustrated a transparent sheet  1804  having a plurality of seal-ring areas  1818  laid out in a rectangular arrangement around a plurality of window portions  1812 . These seal-ring areas  1818  have been first prepared, and then metallized with one or more metal or metal alloy layers, as previously described herein. The transparent sheet  1804  further includes an electrode portion  1830 , which has been metallized, but does not circumscribe any window portions  1812 . This electrode portion is electrically connected to the metallized seal-ring areas  1818  of the sheet. One or more electrode pads  1832  may be provided on the electrode portion  1830  to receive electrical energy from electrodes during the subsequent ERH procedure. 
     Referring now to  FIG. 18   b , there is illustrated a frame  1802  having a plurality of sidewalls  1806  laid out in a rectangular arrangement around a plurality of frame apertures  1808 . The apertures  1808  are disposed so as to correspond with the positions of the window portions  1812  of the sheet  1804 , and the sidewalls  1806  are disposed so that frame seal-ring areas  1810  (located thereupon) correspond with the positions of the sheet seal-ring areas  1818  of the sheet. The frame is metallic or metallized in order to facilitate joining as previously described herein. The frame  1802  further includes an electrode portion  1834  that does not circumscribe any frame apertures  1808 . This frame electrode portion  1834  is positioned so as not to correspond to the position of the sheet electrode portion  1830 , and preferably is disposed on an opposing side of the sheet-window/frame-grid assembly (i.e., when the sheet is assembled against the frame). The frame electrode portion  1834  is electrically connected to the metallized frame seal-ring areas  1810 . One or more electrode pads  1836  may be provided on the electrode portion  1834  to receive electrical energy from electrodes during the subsequent ERH procedure. 
     Referring now to  FIG. 18   c , the sheet  1804  is shown positioned against the frame  1802  in preparation for heating to produce the hermetic seal therebetween. If applicable, solder or a solder preform has been positioned therebetween as previously described. It will be appreciated that when the transparent sheet  1804  is brought against the frame  1802 , the metallized seal-ring areas  1818  on the lower surface of the sheet will be in electrical contact with the metallized seal-ring areas  1810  on the upper surface of the frame. However, the sheet electrode portion  1830  and the frame electrode portion  1834  will not be in direct contact with one another, but instead will be electrically connected only through the metallized seal-ring areas  1818  and  1810  to which they are, respectively, electrically connected. When an electrical potential is applied from electrode pads  1832  to electrode pads  1836  (denoted by the “+” and “−” symbols adjacent to the electrodes), electrical current flows through the junction region of the entire sheet-window/frame-grid assembly. This current flow produces electrical resistance heating (ERH) due to the resistance inherent in the metallic layers. In some embodiments, this electrical resistance heating may be sufficient to supply the necessary heat, in and of itself, to result in TC bonding, soldering, or other hermetic seal formation between the sheet  1804  and the frame  1802  in order to form a multi-unit assembly. In other embodiments, however, electrical resistance heating may be combined with other heating forms such as furnace or oven pre-heating in order to supply the necessary heat required for bonding to form the multi-unit assembly. 
     After bonding the sheet  1804  to the frame  1802  to form the multi-unit assembly, the sheet electrode portion  1830  and the frame electrode portion  1834  can be cut away and discarded, having served their function of providing electrical access for external electrodes (or other electrical supply members) to the metallized seal-ring areas of the sheet and frame, respectively. The removal of these “sacrificial” electrode portions  1830  and  1834  may occur before or during the “dicing” process step, i.e., the separating of the multi-unit assembly into individual cover assemblies. It will be appreciated that any of the technologies previously described herein for separating a multi-unit assembly into individual cover assemblies can be used for the dicing step of separating a multi-unit assembly fabricated using ERH heating. 
     Where ERH is to be used for manufacturing multiple cover assemblies simultaneously, the configuration of the sheet-window/frame-grid array and/or the placement of the electrodes portions within the sheet-window/frame-grid array may be selected to modify the flow of current through the junction region during heating. The primary type of modification is to even the flow of current through the various portions of the sheet-window/frame-grid during heating to produce more even temperatures, i.e., to avoid “hot spots” or “cold spots.” 
     Referring now to  FIGS. 19   a - 19   f , there are illustrated various sheet-window/frame-grid configurations adapted for producing more even temperatures during ERH. In each of  FIGS. 19   a - 19   f , there is shown a sheet-window/frame-grid array  1900  comprising a prepared, metallized transparent sheet  1904  overlying a prepared, metallic/metallized frame  1902 . The window portions of the sheet  1904  directly overlie the frame apertures of the frame  1902 , and the metallized seal-ring areas of the sheet directly overlie the seal-ring areas of the frame (it will be appreciated that metallized portions of the sheet  1904  and the frame  1902  appear coincident in these figures). Metallized electrode portions formed on the transparent sheet  1904  are denoted by reference letters A, B, C and D. These electrode portions A, B, C and D are electrically connected to the adjoining sheet seal-ring areas of the sheet, but are electrically insulated from one another by non-metallized areas  1906  of the sheet. An external electrode is applied to the top of the metallic/metallized frame (on the side opposite from the sheet) across the area denoted by reference letter E. For bonding or soldering, electrical power is applied at the electrodes, e.g., one line to electrodes A, B, C and D simultaneously, and the other line to electrode E, or alternatively, one line in sequence to each of electrode A, B, C and D, and the other line to electrode E. It will be appreciated that many other combinations of electrode powering are within the scope of the invention. 
     Referring to  FIG. 19   f , this embodiment illustrates a sheet-window/frame-grid  1900  having a “shingle” configuration, i.e., where the seal-ring areas between the window portions/frame apertures do not form continuous straight lines across the assembly array. Shingle-arrangement frame assemblies are more labor-intensive to separate using scribe-and-break or cutting procedures. Separating such assemblies requires that each row first be separated from the overall grid, and then that individual cover assemblies be separated from the row by separate scribe-and-break or cutting operations. Nevertheless, use of shingle-arrangement assemblies may have benefits relating to heating using ERH techniques. 
     It will be understood that a metal frame such as  1802  or  1902 , which may contain one or more added layers on its exterior, including but not limited to metal or metal alloy layers, may be diffusion bonded to a non-metallized sheet using ERH techniques to apply heat to the frame. The amount of temperature rise throughout the thickness of the non-metallized sheet will depend on the intensity and duration of the application of the electrical power (voltage and amperage) to the frame, as well as other factors. An innerlayer or interlayer material may be employed between the frame and the sheet during the diffusion bonding process, as discussed previously. 
     It will further be appreciated that the terms “thermal compression bonding” (and its abbreviation “TC bonding”) and “diffusion bonding” are used interchangeably throughout this application. The term “diffusion bonding” is preferred by metallurgists while the term “thermal compression bonding” is preferred in many industries (e.g., semiconductor manufacturing) to avoid possible confusion with other types of “diffusion” processes used for creating semiconductor devices. Regardless of which term is used, as previously discussed, diffusion bonding refers to the family of bonding methods using heat, pressure, specific positive or negative pressure atmospheres and time alone to create a bond between mating surfaces at a temperature below the normal fusing temperature of either mating surface. In other words, neither mating surface is intentionally melted, and no melted filler material is added, nor any chemical adhesives used. 
     As previously described, diffusion bonding utilizes a combination of elevated heat and pressure to hermetically bond two surfaces together without first causing one or both of the adjoining surfaces to melt (as is the case with conventional soldering, brazing and welding processes). When making optical cover assemblies, wafer level assemblies or other temperature-sensitive articles, it is almost always required that the bonding temperatures remain below some upper limit. For example, in optical cover assemblies, the bonding temperature should be below the T G  and the softening temperature, T S , of the sheet material so as not to affect the pre-existing optical characteristics of the sheet. As another example, in wafer level assemblies, the bonding temperature should be below the upper temperature limit for the embedded micro device and/or its operating atmosphere (i.e., the gas environment inside the sealed package). However, the specific temperature and pressure parameters required to produce a hermetic diffusion bond can vary widely depending upon the nature and composition of the two mating surfaces being joined. Therefore, it is possible that some combinations of transparent sheet material (e.g., glass) and frame material (e.g., metals or metallized non-metals), or some combinations of frame materials and substrate materials (e.g., silicon, alumina or metals), will have a diffusion bonding temperature that exceeds the T G  and/or the T S  of the sheet material, or that exceeds some other temperature limit. In such cases, it might appear that diffusion bonding is unsuitable for use in hermetically joining the components together if the temperature limits are to be followed. In fact, however, it has been discovered that the use of “interlayers,” i.e., intermediate layers of specially selected material, placed between the sheet material and the frame, or between the frame material and the substrate material, can cause hermetic diffusion bonding to take place at a substantially lower temperature than if the same sheet material was bonded directly to the same frame material, or if the same frame material was bonded directly to the same substrate material. Note that the terms “interlayers” and “innerlayers” are used interchangeably throughout this application, as both terms may be encountered in the art for the same thing. 
     A properly matched interlayer improves the strength and hermeticity (i.e., gas tightness or vacuum tightness) of a diffusion bond. Further, it may promote the formation of compatible joints, produce a monolithic bond at lower bonding temperatures, reduce internal stresses within the bond zone, and prevent the formation of extremely stable oxides which interfere with diffusion, especially on the surface of Al, Ti and precipitation-hardened alloys. The interlayer is believed to diffuse into the parent material, thereby raising the melting point of the joint as a whole. Depending upon the materials to be joined by diffusion bonding, the interlayer material could be composed of a metal, a metal alloy, a glass material, a solder glass material including solder glass in tape or sheet form, or other materials. In the diffusion bonding of BT5-1 Ti alloy to Armco iron, an interlayer of molybdenum foil 0.3 mm thick has been used. Reliable glass-to-glass and glass-to-metal bonds are achieved with metal interlayers such as Al, Cu, Kovar, Niobium and Ti in the form of foil, usually not over 0.2 mm thick. The interlayers are typically formed into thin preforms shaped like the seal ring area of the mating surfaces to be joined. 
     It is important to distinguish the use of diffusion bonding interlayers from the use of conventional solder preforms and other processes previously disclosed. For purposes of this application, an interlayer is a material used between sealing surfaces to promote the diffusion bonding of the surfaces by allowing the respective mating surfaces to diffusion bond to the interlayer rather than directly to one another. For example, with the proper interlayer material, the diffusion bonding temperature for the joint between the sheet material and interlayer material, and for the joint between the interlayer material and the frame material, may be substantially below the diffusion bonding temperature of a joint formed directly between the sheet material and the frame material. Thus, use of the interlayer allows diffusion bonding of the sheet to the frame at a temperature which is substantially below the diffusion bonding temperature that would be necessary for bonding that sheet material and that frame material directly. The hermetic joint is still formed by the diffusion bonding process, i.e., none of the materials involved (the sheet material, the interlayer material nor the frame material) melts during the bonding process. This distinguishes diffusion bonding using interlayers from other processes such as the use of solder preforms in which the solder material actually melts to form the bond between the materials being joined. It is possible to use materials conventionally used for solders, for example, Au—Sn solder preforms, as interlayers for diffusion bonding. However, when used as interlayers they are used for their diffusion bonding properties and not as conventional solders (in which they melt). 
     The use of interlayers in the production of window assemblies or other packaging may provide additional advantages over and above their use as promoting diffusion bonding. These advantages include interlayers which serve as activators for the mating surfaces. Sometimes the interlayer materials will have a higher ductility in comparison to the base materials. The interlayers may also compensate for stresses which arise when the seal involves materials having different coefficients of thermal expansion or other thermal expansion properties. The interlayers may also accelerate the mass transfer or chemical reaction between the layers. Finally, the interlayers may serve as buffers to prevent the formation of undesirable chemical or metallic phases in the joint between components. 
     Referring now to  FIGS. 20   a  and  20   b , there is illustrated a window cover assembly including interlayers to promote joining by diffusion bonding. In this embodiment, the window assembly  2050  includes a transparent glass sheet  2052 , an interlayer  2054  and a metal or metal alloy base  2056 . The base  2056  includes a built-up seal ring area  2058  and a flange  2060  which facilitates the subsequent electric resistance seam welding of the finished window assembly to a package base or other higher level portion of the final component. The interlayer  2054  in this embodiment takes the form of a metallic preform which has the configuration selected to match the seal ring area  2058  of the frame. To form the hermetic window assembly, the sheet  2052 , interlayer  2054  and frame  2056  are placed in a fixture (i.e., tooling) or mechanical apparatus (not shown) which can provide the required predetermined bonding pressure between the seal ring areas of the respective components. In some cases, the fixture may serve only to align the components during bonding, while the elevated bonding pressure is applied from a mechanical apparatus such as a ram. In other cases, however, the fixture may be designed to constrain the expansion of the stacked components during heating (i.e., along the stacking axis), whereby the thermal expansion of the assembly components toward the fixture, and of the fixture itself toward the components, will “self-generate” some or all of the necessary bonding pressures between the components as the temperature increases. 
     Referring now to  FIGS. 20   e  and  20   f , an example of a “self-compressing” fixture assembly is shown. As best seen in  FIG. 20   e , the fixture  2085  includes an upper fixture member  2086  and a lower fixture member  2087 , which together define a cavity  2088  for receiving the window assembly components to be bonded. Clamps  2089  are provided which constrain the outward movement of the fixture members  2086  and  2087  in the axial direction (denoted by arrow  2090 ). Generally, the CTE of the material forming the clamps  2089  will be lower than the CTE of the material forming the fixture members  2086  and  2087 .  FIG. 20   f  shows the components for the window assembly  2070  ( FIGS. 20   c  and  20   d ) loaded into the cavity  2088  of the fixture  2085  in preparation for bonding. Note that while the fixture members  2086  and  2087  are in contact with the upper and lower surfaces of the window components, a small gap  2097  is left between the fixture members themselves to allow the members to expand axially toward one another when heated (since they are constrained by the clamps). Also, note that a small gap  2098  is generally left between the lateral sides of the window assembly components and the fixture members  2086  and  2087  to minimize the lateral force exerted on the components by the fixture members during heating. When the fixture  2085  is heated, the inner surfaces (i.e., facing the cavity  2088 ) of the fixture members  2086  and  2087  will expand (due to thermal expansion) axially toward one another against the window components, and the window components will expand outward against the fixture. These thermal expansions can press the window components against one another with great force in the axial direction to facilitate diffusion bonding. It will be appreciated that thermal expansion of the fixture members  2086  and  2087  will also occur in the lateral direction (denoted by arrow  2091 ). While this lateral expansion is not generally desired, in most cases is will not present an obstacle to the use of self-compressing fixtures. 
     Referring now to  FIG. 20   g , there is illustrated an alternative self-compressing fixture adapted to enhance thermal expansion (and hence compression) in the axial direction  2090  without causing excessive thermal expansion in the lateral direction  2091 . As with the previous example, alternative fixture  2092  includes an upper fixture member  2086  and a lower fixture member  2087  defining a cavity  2088  for receiving the window assembly components to be bonded, and clamps  2089  (only one of which is shown for purposes of illustration) which constrain the outward movement of the fixture members in the axial direction  2090 . Also as in the previous embodiment, a first small gap  2097  is present between the fixture members  2086  and  2087  themselves, and a second small gap  2098  is present between the lateral sides of the window components and the fixture members. Unlike the previous embodiment, however, each fixture member  2086  and  2087  of the alternative fixture  2092  comprises two sub-members, namely, first sub-members  2093  and  2094 , respectively, adapted to bear primarily axially against the window assembly components (not shown), and second sub-members  2095  and  2096 , respectively, adapted to hold and align the window assembly components in the cavity. By selecting a material for the first sub-members  2093  and  2094  having a high CTE, axial expansion (and hence compression) during heating will be correspondingly high. However, lateral expansion and relative lateral movement between the second sub-members  2095  and  2096  and the window components can be minimized by selecting a different material for the second sub-members, namely, a material having a lower CTE (i.e., lower than the CTE for the first sub-members). Preferably, the CTE of the second sub-members  2095  and  2096  will be close to the CTE for the adjacent window components. 
     Referring again to  FIGS. 20   a  and  20   b , the assembled (but not yet bonded) components of the window assembly  2050  are then heated until the diffusion bonding pressure/temperature conditions are reached, and these conditions are maintained until a first diffusion bond is formed between the sheet  2052  and the interlayer  2054 , and a second diffusion bond is formed between the interlayer  2054  and the seal ring area  2058  of the frame  2056 . It will be understood that the first bond between the sheet and the interlayer may actually occur before, after or simultaneously with, the second bond between the interlayer and the frame. As previously explained, it will also be understood that the order of applying heat and pressure to form the diffusion bond is not believed to be significant, i.e., in other words whether the pre-determined pressure is applied, and then the heat is applied or whether the heat is applied and then the predetermined pressure is applied, or whether both heat and pressure are increased simultaneously is not believed to be significant, rather the diffusion bonding will occur when the preselected pressure and temperature are present in the bond region for a sufficient amount of time. After the diffusion bonds are formed, the sheet  2052  will be hermetically bonded to the frame  2056  to form a completed window assembly  2050  as shown in  FIG. 20   b.    
     In further embodiments of the current invention, it has been discovered that clean, i.e., unmetallized, glass windows may be directly bonded to frames of Kovar or other metallic materials using diffusion bonding. This is in addition to the diffusion bonding of metallized glass windows to Kovar frames as previously described. Optionally, the direct diffusion bonding of unmetallized glass windows to metallic frames may be enhanced through the use of certain compounds, e.g., molybdenum-manganese, on the frames. Whether the glass is metallized or unmetallized, the diffusion bonding is most commonly performed in a vacuum; however, it may be performed in various other atmospheres. The use of oxidizing atmospheres is typically not required, however, as any resulting oxides tend to be dispersed by pressures encountered in the bonding operation. In still other embodiments, of the invention, diffusion bonding can be used for joining frames made of Kovar and other metallic materials directly to sheets or wafers of semiconductor materials including silicon and gallium arsenide (GaAs). 
     Since successful diffusion bonding requires the mating surfaces being bonded to be brought into intimate contact with one another, the surface finish characteristics of the mating surfaces may be important parameters of the invention. It is believed that the following mating surface parameters will allow successful diffusion bonding between the mating surfaces of Kovar frames and thin sheet materials including, but not limited to, Kovar to metallized glass, Kovar to clean (i.e., unmetallized) glass, Kovar to metallized silicon, Kovar to clean (i.e., unmetallized) silicon, Kovar to metallized gallium arsenide (GaAs) and Kovar to clean (i.e., unmetallized) GaAs: Parallelism of sheet material (i.e., uniformity of thickness) within the range of ±about 12.7° microns; Surface flatness (i.e., deviation in height per unit length when placed on ideal flat surface) within range from 5 mils/inch to about 10 mils/inch; Surface roughness not more than about 16 micro-inches (0.4064 microns). These surface parameters can also be used for diffusion bonding of Kovar directly to Kovar, e.g., to manufacture built-up metallic frames. 
     The temperature parameters for diffusion bonding between the mating surfaces of Kovar frames and the thin sheet materials described above are believed to be within the range from about 40% to about 70% of the absolute melting temperature, in degrees Kelvin, of the parent material having the lower melting temperature. When diffusion bonding is used for bonding optically finished glass or other transparent materials, the bonding temperature may be selected to be below the T G  and/or the softening temperature of the for the glass other transparent materials, thereby avoiding damage to the optical finish. Depending upon the bonding temperature selected, in some embodiments the application of optical and/or protective coatings to the transparent sheets (i.e., that become the windows) may be performed after the bonding of the sheets to the frames, rather than before bonding. In other embodiments, some of the optical and/or protective coatings may be applied to the glass sheets prior to bonding, while other coatings may be applied subsequent to bonding. With regard to pressure parameters, a pressure of 105.5 kg/cm 2  (500 psi) is believed suitable for diffusion bonding Kovar frames and the thin sheet materials previously described. 
     It will be noted that since the diffusion bonding occurs at high temperature, the CTE of the glass sheet should be matched to the CTE of the metallic frame. To the extent that the CTEs cannot be completely matched (e.g., due to non-linearities in the CTEs over the range of expected temperatures), then it is preferred that the CTE of the glass sheet be lower than the CTE of the metallic frame. This will result in the metallic frame shrinking more than the glass sheet as the combined window/frame assembly cools from its elevated bonding temperature (or from an elevated operational temperature) back to room temperature. The glass will therefore be subjected primarily to compression stress rather than tension, which reduces the tendency for cracking. 
     Referring now to  FIGS. 20   c  and  20   d , there is illustrated an additional embodiment of the invention, a window assembly having internal and external frames.  FIG. 20   c  illustrates the components of window assembly  2070  before assembly, while  FIG. 20   d  illustrates the completed assembly. The window assembly  2070  includes separate frame members  2072  and  2074 , which are bonded (using diffusion bonding, soldering, brazing or other techniques disclosed herein) to the inner and outer surfaces  2076  and  2078 , respectively, of the transparent sheet  2080 . In other words, the transparent window material is “sandwiched” between a layer of frame material on the top of the window and a layer of frame material on the bottom of the window. Interlayers  2082  and  2084  may be provided for diffusion bonding as previously described, or alternatively, solder preforms (also shown as  2082  and  2084 ) may be provided for bonding by soldering as previously described. 
     Typically, the same bonding technique will be used for bonding both the internal and external frames to the window, however, this is not required. Similarly, the internal and external bonds will typically be formed at the same time, however, this in not required. The internal frame  2072  must, however, be hermetically bonded to the window  2080  to produce a hermetic window assembly. A hermetic bond is not typically required for bonding the external frame  2074  to the window  2080 , however, it may be preferred for a number of reasons. 
     One benefit of window assemblies having the so-called “sandwiched” frame configuration is to equalize the stresses on the internal and external surfaces,  2076  and  2078 , respectively, of the transparent sheet  2080  that are caused by differential thermal expansion characteristics of the frames  2072  and  2074  and sheet (due to unequal CTE), e.g., during cooling after bonding, or during thermal cycling. Put another way, when a window assembly has a frame bonded to only one surface, uneven expansion and contraction between the frame and sheet may produce significant shear stresses within the sheet. These shear stresses may be strong enough to cause shear failure (e.g., cracking or flaking) within the transparent sheet even though the window-to-frame bond itself remains intact. When a frame is bonded to both the internal and external surfaces of the window, however, the shear stresses within the glass (or other transparent material) may be significantly reduced. This is particularly true if the same material or material having similar CTEs are used for both the internal and external frames. This stress-equalization through the thickness of the window increases the reliability and durability of the assembled window during subsequent thermal cycling and/or physical shock. 
     Sandwiched construction may be used in window assemblies or in WLP assemblies. Sandwiched construction with internal and external frames is especially advantageous where the sheet and frame materials have significantly different CTEs. In addition to the stress balancing features of sandwiched construction, use of an external frame on the sheet may have additional benefits, including: enhancing thermal spreading across the window; enhancing heat dissipation from the assembly; serving as an optical aperture; facilitating the aligning/fixturing or clamping of the device during bonding or assembly to higher level assemblies; and to display working symbolization. 
     Referring now to  FIGS. 21   a  and  21   b , there are illustrated two examples of hermetically sealed wafer-level packages (also known as “WLPs”) for micro-devices in accordance with other embodiments of the invention. These embodiments are substantially similar to one another, except that wafer-level package  2002  ( FIG. 21   a ) has reverse-side external electrical connections while wafer-level package  2024  ( FIG. 21   b ) has same-side external electrical connections. The wafer-level packages, while similar in many respects to the discrete device packages previously disclosed herein, utilize the substrate of the micro-device itself, typically a semiconductor substrate, as a portion of the package&#39;s hermetic envelope. Such wafer-level packaging provides a very economical method for hermetically encapsulating wafer-fabricated micro-devices, especially where high production volumes are involved. As will be described below, a single micro-device may be packaged using WLP technology, or multiple micro-devices on the original production wafer may be packaged simultaneously using WLP technology in accordance with various aspects of the current invention. 
     Referring now specifically to  FIG. 21   a , the wafer-level package  2002  encloses one or more micro-devices  2004 , e.g., a MEMS device or MOEMS device fabricated on a substrate  2006 . The substrate  2006  is typically a wafer of silicon (Si) or gallium arsenide (GaAs) upon which electronic circuitry  2008  associated with the micro-device  2004  is formed using known semiconductor fabrication methods. Electrical vias  2010  (shown in broken line) may be formed in the substrate  2006  using known methods to connect the circuitry  2008  to externally accessible connection pads  2012  disposed on the reverse side (i.e., with respect to the device) of the substrate. It will be appreciated that the path of vias  2010  shown in  FIG. 20  has been simplified for purposes of illustration. One end of a frame  2014  made of Kovar or other metallic material is hermetically bonded to the substrate  2006 , and a transparent window  2016  is, in turn, hermetically bonded to the other end of the frame to complete the hermetic envelope sealing the micro-device within the cavity  2018 . The frame-mating surfaces of the substrate  2006  may be prepared or metallized with one or more metal layers  2020  to facilitate bonding to the frame, and similarly the frame-mating surfaces of the window  2016  may be prepared or metallized with one or more metal layers  2022  for the same purpose. 
     Referring now specifically to  FIG. 21   b , the wafer-level package  2024  is substantially identical to the package  2002  previously described, except that in this case the vias  2026  are routed to external connection pads  2028  disposed on the same side of the substrate  2006 . Obviously, in such embodiments, the frame  2014  and window  2016  are dimensioned to leave uncovered a portion of the substrate&#39;s upper surface. 
     Referring now to  FIG. 21   c , there is shown an exploded view of a WLP  2100  illustrating one possible method of manufacture. To package individual or multiple micro-devices using WLP methods, the following components are necessary: a substrate  2006  having a micro-device  2004  thereupon; a frame/spacer  2014  having a continuous sidewall  2015  and that is “taller” than the device to be encapsulated (to provide clearance); and a transparent sheet or window  2016 . Depending upon the bonding method to be used, solder preforms of a metal alloy or glass composition, or interlayers for diffusion bonding  2102  and  2103  may also be required. It will be appreciated that the top preform  2102  (between the window  2106  and the frame  2014 ) may be a different material than the bottom preform  2103  (between the frame  2014  and the substrate  2006 ). 
     Briefly, the steps for forming the package  2100  are as follows: A first frame-attachment area  2104  is prepared on the surface of the wafer substrate  2006  of the subject micro-device. This first frame-attachment area  2104  has a plan (i.e., configuration when viewed from above) that circumscribes the micro-device or micro-devices  2004  on the substrate  2006 . A second frame-attachment area  2106  is prepared on the surface of the window  2016 . The second frame-attachment area  2106  typically has a plan substantially corresponding to the plan of the first frame-attachment area  2104 . The execution order of the previous two steps is immaterial. Next, the frame/spacer  2014  is positioned between the substrate  2006  and the window  2016 . The frame/spacer  2014  has a plan substantially corresponding to, and in register with, the plans of the first and second frame-attachment areas  2104  and  2106 , respectively. If applicable, the solder preforms  2102  and  2103  or diffusion bonding interlayers  2102  and  2103  are interposed at this time between the frame/spacer  2014  and the frame-attachment areas  2104  and/or  2106 . Finally, the substrate  2006 , frame/spacer  2014  and window  2016  are bonded together (facilitated by solder or glass preforms  2102  and  2103  or diffusion bonding interlayers  2102  and  2103 , if applicable) to form a hermetically sealed package encapsulating micro-device  2004  within, but allowing light to travel to and/or from the micro-device through the transparent aperture area  2108  of the window. 
     It will be understood that diffusion bonding of the package  2100  can be performed in a single (combined) step or in a number of sub-steps. For example, all five components (sheet  2016 , first interlayer  2102 , frame  2014 , second interlayer  2103  and substrate  2006 ) could be stacked in a single fixture and simultaneously heated and pressed together to cause diffusion bonds to form at each of the sealing surfaces. Alternatively, the window sheet  2016  may be first diffusion bonded to the frame  2014  using first interlayer  2102  (making a first subassembly), and then this first subassembly may be subsequently diffusion bonded to the substrate  2006  using second interlayer  2103 . In another alternative, the frame  2014  could be diffusion bonded to the substrate  2006  using second interlayer  2103 , and then the transparent sheet  2016  may subsequently be bonded to the sub-assembly using first interlayer  2102 . The choice of which bonding sequence to be used would, of course, depend upon the exact materials to be used, the heat sensitivity of the transparent material in the sheet  2016 , the heat sensitivity of the micro device  2004  and, perhaps, other parameters such as the expansion characteristics of the frame  2014  and interlayer materials. 
     It will further be appreciated that the current invention is similar in several respects to the manufacturing of the “stand-alone” hermetic window assemblies previously described. The preparing of the frame-attachment areas  2106  of the window  2016  may be performed using the same techniques previously described for use in preparing the sheet seal-ring area  318 , including cleaning, roughening, and/or metallizing with one or more metallic layers as set forth in the earlier Examples 1-96. 
     While the transparent windowpane  2016  may be roughened (e.g., in preparing the frame-attachment area  2106 ) to promote adhesion of the first metallic layer being deposited onto it (e.g., by CVD or PVD), the wafer substrate  2006  will not typically be roughened in the same manner. Instead, the initial metallic layer on the wafer substrate  2006  will typically be deposited using conventional wafer fabrication techniques. Where conventional methods of wafer fabrication include the requirement or option of etching a silicon or GaAs wafer to promote adhesion of a metal&#39;s deposition, then the same practice may be followed in preparing the frame attachment area  2104  on the wafer substrate  2006  when building WLP devices. 
     Other wafer or substrate materials include, but are not limited to, glass, diamond and ceramic materials. Some ceramic wafers are known as alumina wafers. These alumina wafers or substrates may be multi-layer substrates, and may be manufactured using Low-Temperature Co-Fired (LTCC) or High-Temperature Co-Fired (HTCC) materials and processes. LTCC and HTCC substrates often have internal and external electrical circuitry or interconnections. This circuitry is typically screen printed onto the ceramic or alumina material layer(s) prior to co-firing the layers together. 
     Also, any of the bonding techniques and parameters previously described for use on window assemblies may be used to hermetically bond the WLP components to one another, including diffusion bonding/TC bonding with or without the use of interlayers, soldering using a solder preform and soldering using inkjet-dispensed solders. The primary difference is that when making “stand-alone” window assemblies, only two primary components (namely, the transparent sheet/window  304  and frame  302 ) are bonded together, while when making WLPs, three primary components (namely, the window  2016 , frame  2014  and substrate  2006 ) are bonded together (sometimes simultaneously). Of course, when producing WLPs using soldering techniques, additional components may be required, for example one or more solder preforms  2102  or a quantity of inkjet-dispensed solder. The solder preforms, if used, may be attached to the top and/or bottom of the frame  2014  as one step in the manufacture of that item. This will simplify the alignment of the three major components of the WLP assembly. It will, of course, be appreciated that this pre-attachment of the solder preforms to the frame is also applicable to the “stand-alone” window assemblies previously described. One of the methods for attaching solder preforms to the window  2016 , frame  2014  and/or substrate  2006  is to tack the preform in place using a localized heat source. 
     Prior to soldering components together, cleaning the surfaces of the solder preforms and/or the metallized surfaces of the window  2016 , frame  2014  and/or substrate  2006  may be necessary to remove surface oxides. It is desirable to avoid using fluxes during the soldering process to eliminate the need for post-soldering or defluxing. Several surface preparation technologies are available to prepare the metal and solder surfaces for fluxless soldering. 
     Several other processes may be used for preparing the surfaces of window assemblies or WLP components for soldering to avoid the need to remove fluxes after soldering. A first option is to use what is known in the trade as a no-clean flux. This type of flux is intended to be left in place after soldering. A second option is the use of gas plasma treatments for improving solderability without flux. For example, a non-toxic fluorine-containing gas may be introduced that reacts at the surface of the solder. This reaction forms a crust on the solder and dissolves upon remelt. The welds and joints formed are equal to or better than those formed when using flux. Such plasmas offer benefits including the removal by reduction of oxides and glass to promote improvements in solderability and wire bondability. Such treatments have been indicated on thick film copper, gold and palladium. Additional candidate gases for leaving a clean oxide-free surface include hydrogen and carbon monoxide plasma. Still further candidate gases include hydrogen, argon and freon gas combinations. One version of plasma treatment is known as Plasma-Assisted Dry Soldering (PADS). The PADS process coverts tin oxide (present in fluxless solders when unstable reduced tin oxide reoxidizes upon exposure to air) to oxyfluorides that promote wetting. The conversion film breaks up when the solder melts and allows reflow. The film is understood to be stable for more than a week in air and for more than two weeks when the parts are stored in nitrogen. 
     As in the previously described methods for manufacture of individual and multiple window assemblies for hermetically packaging discrete micro-devices, the selection of compatible materials for the various components for the manufacture of WLPs is another aspect of the invention. For example, each of the primary components (e.g., window, frame/spacer and wafer substrate) of the WLP will preferably have closely matched CTEs to insure maximum long-term reliability of the hermetic seal. The frame/spacer  2014  may be formed of either a metallic material or of a non-metallic material. The best CTE match will be achieved by forming the frame/spacer  2014  from the same material as either the wafer substrate  2006  or the window  2016 . However, gallium arsenide (GaAs) and silicon (Si) (i.e., the materials typically used for the wafer substrate) and most glasses (i.e., the material that is typically used for the window) are relatively brittle, at least in comparison to most metals and metal alloys. These non-metallic materials are therefore typically not as preferred for forming the frame/spacer  2014  as are metals or metal alloys, because the metals and metal alloys typically exhibit better resistance to cracking. In fact, the use of a metal or metal alloy for the frame/spacer  2014  is believed to provide additional resistance to accidental cracking or breaking of the wafer substrate  2006 , window  2016  and complete WLP  2002  after bonding. When a metallic frame/spacer  2014  is employed, it will preferably be plated with either gold alone, or with nickel and then gold, sometimes to facilitate diffusion bonding or soldering, but more often, to provide a surface on the frame/spacer that provides various kinds of protection between the frame/spacer and the atmosphere inside the package. If, however, a non-metallic frame/spacer  2014  is employed, then it might be metallized to facilitate diffusion bonding or soldering. The metal layers used on the frame/spacer  2014  may be the same as those used on the windowpane  304  for the manufacture of window assemblies, e.g., the final layer might be one of chromium, nickel, tin, tin-bismuth and gold. 
     In selecting compatible materials for the components of WLPs, it is recognized that silicon (Si) has a CTE ranging from about 2.6 PPM/° K at 293° K to about 4.1 PPM/° K at 1400° K. If it is assumed that the operating temperatures for micro-devices such as MEMS and MOEMS will be within the range from about −55° C. to about +125° C., and that the expected diffusion bonding or soldering temperatures will be within the range from about +250° C. to about +500° C., it may be interpolated that silicon wafers of the type used for WLP substrates will have a CTE within the range from about 2.3 PPM/° K to about 2.7 PPM/° K. One metallic material believed suitable for use in frame/spacers  2014  that will be bonded to silicon (Si) substrates is the alloy known as “Low Expansion 39 Alloy,” developed by Carpenter Specialty Alloys. Low Expansion 39 Alloy is understood to have a composition (weight percent; nominal analysis) as follows: about 0.05% C, about 0.40% Mn, about 0.25% Si, about 39.0% Ni, and the balance Fe. Low Expansion 39 Alloy has a CTE that is understood to range from about 2.3 PPM/° K over the interval of 25° C. to 93° C., to about 2.7 PPM/° K at 149° C., to about 3.2 PPM/° K at 260° C., and to about 5.8 PPM/° K at 371° C. 
     Similarly, it is recognized that gallium arsenide (GaAs) of the type used for WLP wafer substrates has a nominal CTE of about 5.8 PPM/° K. Based on material suppliers&#39; data, Kovar alloy is understood to have a CTE ranging from about 5.86 PPM/° K at 20° C. to about 5.12 PPM/° K at 250° C. Thus, Kovar alloy appears to be a good choice for frame/spacers  2014  that will be bonded to GaAs substrates. Another material believed suitable for frame/spacers  2014  that will be bonded to GaAs substrates is the alloy known as Silvar™, developed by Texas Instruments Inc.&#39;s Metallurgical Materials Division, of Attleboro, Mass. It is understood that Silvar™ is a derivative of Kovar with CTE characteristics closely matched to GaAs devices. 
     With regard to the window/lens for WLPs, it is believed that all of the glasses previously described for use in the manufacture of individual and multiple window assemblies having Kovar frames, e.g., Corning 7052, 7050, 7055, 7056, 7058 and 7062, Kimble (Owens Corning) EN-1, Kimble K650 and K704, Abrisa soda-lime glass, Schott 8245 and Ohara Corporation S-LAM60, will be suitable for the window/lens  2016  of WLPs having a GaAs substrate  2006 . Pyrex glasses and similar formulations are believed suitable for the window/lens  2016  of WLPs having silicon substrates  2006 . The properties of Pyrex, per the Corning website, are: softening point of about 821° C., annealing point of about 560° C., strain point of about 510° C., working point of about 1252° C., expansion (0-300° C.) of about 32.5×10 −7 /° C., density of about 2.23 g/cm 3 , Knoop hardness of about 418 and refractive index (at 589.3 nm) of about 1.474. 
     Referring now to  FIG. 22 , there is illustrated a semiconductor wafer  2202  having a plurality of micro-devices  2204  formed thereupon. It will be appreciated that methods for the production of multiple micro-devices on a single semiconductor wafer are conventional. Heretofore, however, when the micro-devices  2204  are of the type which must be hermetically packaged prior to use, e.g., MEMS, MOEMS, opto-electronic or optical devices, it has been standard practice in the industry to first “individuate” or “singulate” the micro-devices, e.g., by cutting-apart, dicing (apart) or breaking-apart the wafer  2202  into sections having, typically, only a single micro-device on each, and then packaging the individuated micro-devices in separate packages. Now, in accordance with additional embodiments of the current invention, multiple micro-devices may be individually hermetically packaged, or hermetically packaged in multiples, in a WLP prior to individuation or singulation of the substrate wafer. This process is referred to as multiple simultaneous wafer-level packaging, or “MS-WLP.” 
     Referring now to  FIGS. 23 through 29 , there is illustrated one method for MS-WLP of micro-devices. Briefly, this method includes the steps of: a) preparing a first frame-attachment area on the surface of a semiconductor wafer substrate having a plurality of micro-devices, the first frame-attachment area having a plan circumscribing individual (or multiple) micro-devices on the substrate; b) preparing a second frame-attachment area on the surface of a window (i.e., a sheet of transparent material), the second frame-attachment area having a plan substantially corresponding to the plan of the first frame-attachment area; c) positioning a frame/spacer between the substrate and the window, the frame/spacer having a plan substantially corresponding to, and in register with the plans of the first and second frame-attachment areas, respectively; and d) hermetically bonding the substrate, frame/spacer and window together so as to encapsulate the micro-device. If applicable, solder preforms or other materials including, but not limited to, innerlayers of interlayers for diffusion bonding, are also positioned between the frame/spacer and the window and/or substrate before bonding. 
     Referring now specifically to  FIG. 23 , the frame-attachment area  2302  of semiconductor wafer  2202  has been prepared by depositing metallized layers onto the surface of the wafer substrate completely around (i.e., circumscribing) each micro-device  2204 . In the embodiment shown, the prepared frame-attachment area  2302  includes a rectangular grid consisting of double-width metallized rows  2304  and columns  2306  (interposed between the micro-devices  2204 ) surrounded by single-width outer rows  2308  and columns  2310 . The composition and thickness of the metallized layers in frame-attachment area  2302  may be any of those previously described for use in preparing the sheet seal-ring area  318  as set forth in Examples 1-96. 
     Referring now to  FIG. 24 , there is illustrated a MS-WLP frame/spacer  2402  for attachment between the wafer  2202  and the window sheet  2602  of the MS-WLP assembly. It will be appreciated that in this embodiment, the MS-WLP frame/spacer  2402  has double-width row members  2404  and column members  2406  surrounded by single-width outer row members  2408  and column members  2410 , resulting in a plan which corresponds substantially with the plan of the frame-attachment area  2302  on the wafer substrate  2202 . As will be further described below, the purpose of the double-width row and column members  2404  and  2406  is to allow room for cutting the frame during singulation of the MS-WLP assembly after bonding. It will be appreciated that, in other embodiments, the MS-WLP frame/spacer may have a different configuration. In this embodiment, the MS-WLP frame/spacer  2402  is formed of a metal alloy having a CTE substantially matched to the CTE of wafer substrate, however, in other embodiments the frame/spacer may be formed of non-metallic materials as previously described. Also as previously described, the frame/spacer  2402  will preferably be plated or metallized to facilitate the bonding process. 
     Referring now to  FIGS. 25   a - 25   d , there are illustrated details of a preferred configuration for the frame/spacer  2402 .  FIG. 25   a  shows an enlarged plan view of a portion of the double-width column member  2406  and  FIG. 25   b  shows an end view of the same portion. It will be appreciated that the row members  2404  of the frame/spacer  2402  preferably have a similar configuration. The member  2406  is formed to have a “groove”  2502 , or reduced thickness area, running along the central portion of each member, i.e., between the adjacent micro-devices in the completed MS-WLP assembly. As will be further described below, the groove  2502  facilitates cutting apart of the MS-WLP assembly during singulation of the packaged micro-devices. After being cut apart along the groove  2502 , the frame member  2406  will be divided into two single-width members  2504 , each one having the configuration shown in  FIGS. 25   c  and  25   d . During assembly, the grooved side  2505  of the frame member is preferably positioned against the wafer substrate  2202 , while the ungrooved side  2505  is positioned against the window sheet. 
     Referring now to  FIG. 26 , there is illustrated a MS-WLP window sheet  2600  for attachment to the MS-WLP frame/spacer  2402 . The window sheet  2600  is formed of glass or other transparent material having a CTE compatible with the other principal components of the assembly as previously described. At least the inner side (i.e., the side that will be inside the hermetic envelope) of the sheet  2600 , and preferably both sides, must be optically finished. Any desired optical or protective coatings are preferably present on at least the inner side, and preferably on both sides, of the sheet  2600  at this point. However, if the sheet  2600  is attached to only the frame/spacer  2402  in the first of two bonding operations, then the optical or protective coatings may be applied prior to the second, later bonding step of attaching the window assembly to the wafer. A frame-attachment area  2602  is prepared on the MS-WLP window sheet  2600  so as to circumscribe a plurality of window apertures  2603  that will ultimately be aligned with the micro-devices  2204  in the final MS-WLP assembly. In the embodiment shown, the prepared frame-attachment area  2602  takes the form of metallic layers deposited on the sheet  2600  in a rectangular grid consisting of double-width rows  2604  and columns  2606  surrounded by single-width outer rows  2608  and columns  2610 . This results in a plan for the frame-attachment area  2602 , which corresponds substantially with the plan of the frame/spacer  2402 . The composition and thickness of the metallized layers  2604 ,  2606 ,  2608  and  2610  in the frame-attachment area  2602  may be any of those previously described for use in preparing the sheet seal-ring area  318  of the “stand-alone” windows set forth in Examples 1-96. 
     In some embodiments, the inner surface of the window sheet  2600  may be scribed, e.g., with a diamond stylus, through each portion of the frame-attachment area  2602  to facilitate breaking apart of the MS-WLP assembly during singulation. The scribing of the window sheet  2600  would obviously be performed prior to bonding or joining it to the frame/spacer  2402 . Where the frame/spacer  2402  includes grooved members such as those illustrated in  FIGS. 25   a - 25   b , then the scribe lines on the sheet  2600  will preferably be in register with the grooves  2502  of the frame members in the MS-WLP assembly. 
     Referring now to  FIG. 27 , there is illustrated a side view of a complete MS-WLP assembly  2700 . It will be appreciated that the proportions of some of the components shown in  FIG. 27  (e.g., the thicknesses of the metallic layers) may be exaggerated for purposes of illustration. The frame/spacer  2402  is positioned between the wafer substrate  2202  (with associated micro-devices  2204 ) and the window sheet  2600 , with the plans of the frame-attachment areas  2302  and  2602  being substantially in register with the plan of the frame/spacer  2402  such that each micro-device or set of micro-devices  2204  is positioned beneath a window aperture area  2603  of the window sheet. Of course, if the assembly  2700  is bonded using solder technology, then solder preforms (not shown) having a plan substantially corresponding with the frame-attachment areas  2302  and  2602  are also positioned between the frame/spacer  2402  and the frame-attachment areas prior to bonding. Also, if innerlayers or interlayers are used in conjunction with diffusion bonding, these interlayers (not shown) having a plan substantially corresponding with the frame-attachment areas  2302  and  2602  are also positioned between the frame/spacer  2402  and the frame-attachment areas prior to bonding. Any of the previously described bonding technologies may be used to effectuate the bond between the components. The MS-WLP assembly  2700  will look essentially the same before bonding and after bonding (except for incorporation into the bond area of any solder preforms). 
     After bonding, the MS-WLP assembly  2700  is cut apart, or singulated, to form a plurality of hermetically sealed packages containing one or more micro-devices each. There are several options carrying out the singulation procedure. However, since the window sheet  2600 , frame  2402  and wafer substrate  2202  are bonded together, simply scribing and breaking the window sheet (as was done for the multiple stand-alone window assemblies) is not practical. Instead, at least the window sheet  2600  or the wafer substrate  2202  must be cut. The remaining portion may then either be cut, or scribed and broken. It is believed that the best result will be obtained by cutting the wafer substrate  2202  using a wafer-dicing saw, and then either scribing-and-breaking the window sheet  2600 , or cutting the window sheet using a similar dicing saw. 
     Referring now to  FIG. 28 , there is illustrated one option for singulation of a MS-WLP assembly. The MS-WLP assembly  2800  shown in  FIG. 28  is similar in most respects to the assembly  2700  shown in  FIG. 27 , however, in this case the window sheet  2600  was pre-scribed (as denoted by reference number  2802 ) through the metallic layers  2406 , if employed (and also layers  2404  running perpendicular thereto, also if employed) of the interior frame-attachment areas. After bonding, the assembly  2800  is cut from the outer side of the wafer substrate  2202  (as indicated by arrow  2804 ) completely through the substrate and into the groove  2502  of interior frame/spacer members  2606  (and also members  2604  running perpendicular thereto). The cut  2804  does not, however, continue through the window sheet  2600 . Instead, after the wafer substrate  2202  and frame  2402  are cut, the window sheet  2600  is broken by bending it along the pre-scribed lines  2802 . The assembly  2800  may be first broken into rows, then each row broken into individual packages along the column lines, or vice versa. In one variation of this method, the window sheet  2600  is not pre-scribed, but instead is scribed through the kerf  2806  formed by cutting through the wafer substrate  2202  and frame  2402 . It will be appreciated that this scribing must be sufficiently forceful to cut through the remaining portion of the frame member  2406  and metallic layers  2606  under the groove  2502 . The assembly is then broken into individual packages along the scribe lines as before. 
     Referring now to  FIG. 29 , in another variation, a MS-WLP assembly  2900  is individuated by simply cutting completely through the wafer substrate  2202 , frame/spacer  2402  and window sheet  2600  between each micro-device  2204  as indicated by arrow  2902 . The result is a plurality of individually WLP micro-devices  2904 . The individuating cuts may be made from either the window side or the substrate side, however, it may be necessary to protect the outer surface of the window sheet (e.g., with masking tape, etc.) to protect it from damage during the sawing operation. 
     When electrical-resistance heating (“ERH”) is used to facilitate diffusion bonding or soldering of the components of a MS-WLP assembly, the electrical current is typically applied so that it flows through both the window/frame junction and the frame/substrate junction simultaneously. To facilitate this ERH heating, the configuration of the MS-WLP assembly may be modified to provide “sacrificial” metallized areas (i.e., areas that will be discarded later) on the window sheet and wafer substrate for placement of ERH electrodes. Preferably, the electrode placement areas on the substrate and window will be accessible from directions substantially perpendicular to the wafer. 
     Referring now to  FIG. 30 , there is illustrated a wafer  3000  similar in most respects to the wafer  2002  of  FIG. 23 , i.e., having a plurality of micro-devices  2204  formed thereon and a metallized frame-attachment area  3002  formed thereon so as to surround the micro-devices. In this case, however, the wafer  3000  further includes a metallized electrode placement pad  3004  positioned at one end of the wafer. The electrode placement pad  3004  is in electrical contact with the metallized layers  2304 ,  2306 ,  2308  and  2310  of the frame-attachment area  3002 . 
     Referring now to  FIG. 31 , there is illustrated window sheet  3100  similar in most respects to the sheet  2600  of  FIG. 26 , i.e., having a metallized frame-attachment area  3102  formed thereon so as to surround the window aperture areas  2603  on the sheet. In this case, however, the sheet  3100  further includes a metallized electrode placement pad  3104  positioned at one end of the sheet. The electrode placement pad  3104  is in electrical contact with the metallized layers  2604 ,  2606 ,  2608  and  2610  of the frame-attachment area  3102 . 
     Referring now to  FIG. 32 , there is illustrated a MS-WLP assembly  3200  in accordance with another embodiment. The components of the assembly  3200  are positioned such that the wafer substrate  3000  and the window sheet  3100  are adjacent to the frame/spacer  2402 , but the respective metallized electrode placement pads  3004  and  3104  overhang on opposite sides of the assembly. This configuration provides unobstructed access to the pads  3004  and  3104  in a direction perpendicular to the wafer (as denoted by arrows  3202 ), allowing easy attachment of electrodes for ERH procedures. 
     During bonding of WLP assemblies, there are two bonds that should typically occur simultaneously: the junction between the frame/spacer and the window sheet and the junction between the frame/spacer and the wafer substrate. As was described previously, however, the window may first be bonded only to the frame, and later, using ERH, the window/frame assembly can be attached to the substrate of the device. As was previously described in the process for the manufacturing of stand-alone window assemblies, the configuration of the metal frame and placement of ERH electrodes may be critical for even heating using ERH heating techniques. Similarly, for MS-WLP devices, the metallization patterns and ERH electrode placement locations on the wafer substrate and the window sheet may be important to achieving even heating. Therefore, the size/shape of the frame including possibly excess or sacrificial features, and the metallization patterns on both the window sheet and the wafer substrate should be concurrently designed, modeled (e.g., using software simulation) and prototyped to ensure even heating of the bonded surfaces/features. 
     It will be appreciated that the previous embodiment describes a method for manufacturing MS-WLP assemblies which is suited for micro-devices having opposite-side electrical connection pads. Referring now to  FIG. 33 , there is illustrated a micro-device having same-side electrical connections. The micro-device  3300  is disposed on one side of a semiconductor substrate  3302 . A plurality of vias  3304  run from the active areas of the micro-device, through the substrate, and to a plurality of connection pads  3306  located on the same side of the substrate. Obviously, the electrical connection pads  3306  must be accessible even after the micro-device  3300  has been sealed within its hermetic package. In the following embodiment, there is presented another method for manufacturing MS-WLP assemblies suited for use with such micro-devices with same-side connections. 
     Referring now to  FIG. 34 , there is illustrated a wafer  3402  having a plurality of micro-devices  3300  formed thereupon, each micro-device having one or more sets  3403  of associated same-side connection pads  3306 . In accordance with this embodiment, the multiple micro-devices  3300  are individually hermetically packaged in a WLP prior to individuation of the substrate wafer  3402 , however the same-side electrical connection pads  3306  remain accessible. The steps of this embodiment are similar in many respects to those of the previous embodiment, except for the changes described below. 
     Referring now to  FIG. 35 , the frame-attachment area  3502  of the semiconductor wafer  3402  is first prepared, in this case by depositing metallized layers onto the surface of the wafer substrate circumscribing each micro-device  3300 . In the embodiment shown, the prepared frame-attachment area  3502  includes three “ladder-shaped” grids  3503 , each consisting of double-width metallized rows  3504  (i.e., the “rungs” of the ladder) and single-width columns  3506  (the “sides” of the ladder) connected by buss strips  3508  at each end. The composition and thickness of the metallized layers in frame-attachment area  3502  may be any of those previously described for use in preparing the sheet seal-ring area or frame attachment areas. 
     Referring now to  FIG. 36 , there is illustrated a MS-WLP frame/spacer  3602  for attachment between the wafer  3402  and the window sheet  3702  ( FIG. 37 ) of the MS-WLP assembly. It will be appreciated that in this embodiment, the MS-WLP frame/spacer  3602  is configured into multiple ladder shaped portions  3603 , each portion having double-width rung members  3604  and single-width side members  3606  that are configured to have a plan substantially corresponding to the ladder-shaped plans  3503  of the frame-attachment area  3502  on the wafer substrate  3402 . The ladder-shaped portions  3603  are attached to, and held in relative position to one-another by, connecting members  3608  located at opposite ends of the frame/spacer  3602 . As in the previous embodiment, the double-width members  3604  allow room for cutting the frame  3602  between micro-devices during singulation of the MS-WLP assembly (i.e., after bonding). In a preferred embodiment, the double-width members may have a grooved cross-section (e.g., similar to that shown in  FIGS. 25   a  and  25   b ) to facilitate their cutting apart. It will be appreciated however, that in other embodiments the MS-WLP frame/spacer may have a different configuration. In this embodiment, the MS-WLP frame/spacer  3602  is formed of a metal alloy having a CTE substantially matched to the CTE of the wafer substrate; however, in other embodiments the frame/spacer may be formed of non-metallic materials as previously described. Also as previously described, the frame/spacer  3602  will preferably be plated or metallized to facilitate the subsequent bonding process. 
     Referring now to  FIG. 37 , there is illustrated a MS-WLP window sheet  3700  for attachment to the MS-WLP frame/spacer  3602 . The window sheet  3700  is formed of glass or other transparent material having a CTE compatible with the other principal components of the assembly as previously described. At least the inner side (i.e., the side that will be inside the hermetic envelope) of the sheet  3700  (and preferably both sides) is optically finished, and any desired optical or protective coatings are in place on the inner side. Either before or after any desired optical or protective coatings are in place on the inner side of sheet  3700  (and preferably both sides), a frame-attachment area  3702  is prepared on the MS-WLP window sheet  3700  so as to circumscribe a plurality of window apertures  3705  that will ultimately be aligned with the micro-devices  3300  in the final MS-WLP assembly. In the embodiment shown, the prepared frame-attachment area  3702  includes metallic layers deposited on the sheet  3700  in multiple ladder-shaped portions  3703 , each portion including double-width rung members  3704  and single-width side members  3706 . Each ladder portion  3703  has a plan, which corresponds substantially with the plan of the ladder portions  3603  of the frame/spacer  3602 . The methods and procedures for preparation of the window sheet  3700 , including the composition and thickness of the metallized layers  3704  and  3706  in the frame-attachment area  3702 , may be any of those previously described for use in preparing the sheet seal-ring area  318  of the “stand-alone” window assemblies or the frame attachment areas  2602  of the window sheet  2600  of the MS-WLP. 
     In the embodiment illustrated in  FIG. 37 , the metallized layers of window sheet  3700  extend beyond the ladder-shaped portions  3703 , and included additional portions configured to facilitate electric resistance heating (ERH). These additional portions include electrode attachment portions  3708  and bridge portions  3710 , both of which are electrically connected to the metallized layers  3704  and  3706  of the ladder portions  3703 . The configuration, e.g., placement and thickness, of these electrode attachment portions  3708  and bridge portions  3710  are selected to manage the flow of ERH current through the interfaces between the metallized portions of the window sheet  3700  and the frame/spacer  3602 , and through the interface between the frame/spacer  3602  and the metallized portions of the substrate  3402 , thereby controlling the heating at these interfaces during ERH-facilitated bonding operations. 
     As in previous embodiments, the inner surface of the window sheet  3700  may be scribed, e.g., with a laser or diamond stylus, through each portion of the frame-attachment area  3702  to facilitate breaking apart of the MS-WLP assembly during singulation. Where the frame/spacer  3602  includes grooved members such as those illustrated in  FIGS. 25   a - 25   b , then the scribe lines on the window sheet  3700  will preferably be in register with the grooves  2502  of the frame members in the MS-WLP assembly. 
     Referring now to  FIG. 38 , there is illustrated a top view of a complete MS-WLP assembly  3800  including the wafer substrate  3402 , frame/spacer  3602  and window sheet  3700  stacked on one another such that the ladder-shaped areas  3503 ,  3603  and  3703  of each respective component are substantially in register with one another, and such that each of the micro-devices  3300  is positioned beneath a window aperture area  3705  of the window sheet. It will be appreciated that in this embodiment, the configurations of the wafer  3402  and window sheet  3700  are complementary to facilitate the placement of ERH electrodes. Specifically, the portions of the wafer  3402  having the metallized buss strips  3508  project past the edges of the sheet  3700  (when viewed from above), allowing one set of ERH electrodes to make contact from vertically above, while the portions of the sheet having the metallized contact portions  3708  project past the edge of the wafer (when viewed from below), allowing another set of ERH electrodes to make contact from vertically below. 
     Of course, if the assembly  3800  is to be bonded using solder technology, then solder preforms (not shown) having a plan substantially corresponding with the frame-attachment areas are also positioned between the frame/spacer  3602  and the frame-attachment areas of the window sheet  3700  and substrate  3402  prior to bonding. Any of the previously described bonding technologies may be used to effectuate the bond between the components. If the assembly  3800  is to be bonded using diffusion bonding technology, then when using interlayer preforms (not shown), these preforms will have a plan substantially corresponding with the frame-attachment areas and are also positioned between the frame/spacer,  3602  and the frame-attachment areas of the window sheet  3700  and/or between the frame/spacer  3602  and substrate  3402  prior to bonding. The MS-WLP assembly  3800  will look essentially the same before bonding and after bonding (except for incorporation into the bond area of any solder preforms or interlayers for diffusion bonding). 
     After bonding, the window sheet  3700  of the assembly  3800  may be viewed as including primary strip portions  3802 , which overlie the plurality of encapsulated micro-devices  3300 , secondary strip portions  3804 , which are interposed between the primary strips and overlie rows of non-encapsulated contact pads  3403 , and end strip portions  3806 , which are disposed at each end of the window sheet and also overlie rows of non-encapsulated contact pads  3403 . During singulation of the assembly  3800 , the secondary and end strip portions  3804  and  3806 , respectively, of the window sheet are cut away and discarded, these parts being essentially “sacrificial.” Further during singulation, the substrate  3402  is divided along cut lines (denoted by arrows  3808 ) between the columns of micro-devices  3300  and contact pads  3403  to form multi-unit strips. The separating of the window sheet may be performed using saws, lasers or other conventional means, while the dividing of the substrate may be performed using saws, lasers, or by snapping along a score line. 
     Referring now to  FIGS. 39 and 40 , singulation of the MS-WLP assembly  3800  is illustrated. Referring first to  FIG. 39 , there is illustrated a multi-unit strip  3900  which has been separated from the MS-WLP assembly  3800 . The multi-unit strip  3900  includes a plurality of micro-devices  3300  on a portion  3902  of the original wafer substrate  3402 , the micro-devices being encapsulated within adjacent hermetic envelopes having one or more micro-devices under each window portion  3705  of the original window sheet, but with their associated electrical contact pads  3403  being non-encapsulated. The multi-unit strip  3900  is further cut apart, or singulated, along cut lines  3904 , which in this embodiment corresponds to the center of the frame members  3604  separating the adjacent hermetic envelopes. The result is a plurality of discrete hermetically sealed WLP packages containing one or more micro-devices under each window portion  3705 . An example of an individual WLP package  4000  produced by this method is illustrated in  FIG. 40 . 
     During the singulation of multi-unit strips  3900 , at least the window sheet  3700  or the wafer substrate portion  3902  must be cut. The remaining portion may then either be cut, or scribed and broken. It is believed that the best result will be obtained by cutting the wafer substrate portion  3902  using a wafer-dicing saw, and then either scribing-and-breaking the window sheet  3700 , or cutting the window sheet using a similar dicing saw. 
     When making multiple cover assemblies simultaneously, as previously described and illustrated (e.g., in  FIGS. 15   a - 19   f ), or making multiple wafer-level packages simultaneously, as previously described and illustrated (e.g., in  FIGS. 22-40 ), the frame sidewalls between adjacent frame apertures may include reduced cross-sectional thickness areas to facilitate the singulation (i.e., dividing) of the joined multiple-unit assembly into individual window assemblies or individual wafer-level packages. As best seen in  FIGS. 15   a - 16   b ,  17   b ,  25   a - 25   b ,  27  and  32 , this reduced cross-sectional thickness area may take the form of a V-shaped notch formed in the frame sidewalls between adjacent frame apertures. It will be appreciated, however, that alternative frame designs may substituted for those previously illustrated to provide for easier frame fabrication and/or easier singulation of a joined multiple-unit assembly into individual window assemblies or individual wafer-level packages. 
     Referring now to  FIG. 41 , there is illustrated (in side elevation view) a portion of a multiple simultaneous wafer-level packaging assembly  4100  incorporating one alternative frame design. It will be appreciated that the assembly  4100  is shown prior to singulation into individual packages. It will further be appreciated that the assembly  4100  is similar in most ways to the MS-WLP assemblies previously described and illustrated in  FIGS. 27-29 . The assembly  4100  includes a frame  4102  hermetically joined to a wafer substrate  4104  having micro-devices  4106  formed (and/or mounted) thereupon and to a transparent window sheet  4108 , thereby forming a plurality of individual hermetically sealed units  4110  that can be singulated (e.g., along lines  4112 ) between the adjacent frame apertures  4114  to form discrete hermetically sealed packages. Diffusion bonding, or any of the other previously described bonding technologies may be used to effectuate the hermetic seal between the frame  4102 , substrate  4104  and sheet  4108 . As in previous designs, when viewed in plan (i.e., from above as in  FIG. 24 ), the sidewalls of the frame  4102  circumscribe the frame apertures  4114  and have an upper side plan which substantially corresponds to the plan of the predefined frame attachment areas of the sheet  4108 . Also as in previous designs, when viewed in elevation, the sidewalls disposed between adjacent frame apertures  4114  include reduced cross-sectional thickness areas. However, in this embodiment, the reduced cross-sectional thickness areas of the frame  4102  take the form of a relatively thin connecting tab  4116  extending between two relatively thick sidewall members  4118 . In  FIG. 41 , the undivided interior frame sidewall is denoted by reference number  4120 . 
     The connecting tab  4116  of the sidewall  4120  is characterized by a relatively constant vertical thickness T CT , which is significantly smaller than the overall vertical thickness T SW  of the adjacent sidewall members  4118 . Preferably, the value of connecting tab thickness T CT  is less than 25% of the value of the overall sidewall member thickness T SW . More preferably, the value of connecting tab thickness T CT  is less than 10% of the value of sidewall member thickness T SW , and in some cases the value of T CT  is less than 5% of the value of T SW . During fabrication of multiple-unit assemblies, the relatively thin connecting tabs  4116  of this design are sufficiently strong to maintain the structural integrity of the overall frame  4102 . However, during singulation, the relatively thin connecting tabs  4116  can be severed with little chance of damaging or distorting the adjacent, relatively thick sidewall members  4118 , or of damaging the unit&#39;s hermetic seal. In addition, the relatively thin connecting tabs  4116  make it easier for the singulating device, e.g., dicing saw, laser, etc., to cut through the frame&#39;s reduced cross-section area, and sometimes also the substrate  4104  and/or window sheet  4108  in the same operation. 
     Referring now to  FIGS. 42   a - 42   e , there are illustrated several alternative frame designs which can be used for making either multiple cover assemblies simultaneously or multiple wafer-level packages simultaneously. In each figure, there is shown a cross-sectional view of an undivided interior sidewall  4120  having a reduced cross-sectional thickness area comprising a relatively thin connecting tab  4116  extending between two relatively thick sidewall members  4118 . The sidewall  4120  is designed to be singulated along a line denoted by arrow S. It will be understood that the entire frame  4102  will comprise many such sidewalls laid out in a grid pattern to form discrete apertures. The connecting tab  4116  may be positioned at any desired vertical position between the sidewall members  4118 , including, but not limited to, at the top ( FIG. 42   a ), middle ( FIG. 42   c ), bottom ( FIG. 42   e ), upper or lower intermediate positions ( FIGS. 42   b  and  42   d ). It will be appreciated that illustrating all possible vertical locations for the connecting tab  4116  would be impractical, but nonetheless such designs fall within the scope of the current invention, provided that the connecting tab has a relatively constant vertical thickness T CT  that is significantly smaller than the overall vertical thickness T SW  of the adjacent sidewall members  4118 , preferably less than 25% of T SW , more preferably less than 10% of T SW  and sometimes less than 5% of T SW . 
     Referring now to  FIGS. 43   a - 43   e , additional frame designs are illustrated by showing an undivided sidewall  4120  in the same fashion as those of  FIGS. 42   a - 42   e . While a sidewall  4120  may have only a single connecting tab  4116  extending between the sidewall members  4118  ( FIG. 43   a ), it may also have two ( FIGS. 43   b  and  43   c ), three ( FIG. 43   d ), four ( FIG. 43   e ), or even more connecting tabs extending between the sidewall members. Further, these multiple connecting tabs  4116  may be positioned at any desired vertical position between the sidewall members  4118 , including, but not limited to, at the top and bottom ( FIG. 43   b ) or at intermediate positions ( FIG. 43   c ). It will be appreciated that illustrating all possible numbers of connecting tabs  4116  and all possible vertical locations for the connecting tabs would be impractical, but nonetheless such designs fall within the scope of the current invention, provided that each connecting tab has a relatively constant vertical thickness T CT  that is significantly smaller than the overall vertical thickness T SW  of the adjacent sidewall members  4118 , preferably less than 25% of T SW , more preferably less than 10% of T SW  and sometimes less than 5% of T SW . 
     Referring now to  FIGS. 44   a - 44   e , further frame designs are illustrated by showing an undivided sidewall  4120  in the same fashion as those of  FIGS. 42   a - 43   e . While the sidewall members  4118  may be generally rectangular in cross-sectional configuration (as shown in  FIGS. 42   a - 43   e ), this is not required. Rather, the sidewall members  4118  may have cross-sectional configurations which taper (i.e., narrow) as they get vertically farther from the location of the connecting tab  4116 . The connecting tab  4116  may still be positioned at any desired vertical position between the sidewall members  4118 , including, but not limited to, at the top ( FIG. 44   a ), middle ( FIG. 44   c ), bottom ( FIG. 44   e ), upper or lower intermediate positions ( FIGS. 44   b  and  44   d ). This results in some designs with tapers in a single direction (e.g.,  FIGS. 44   a  and  44   e ) and some with tapers in two directions (e.g.,  FIGS. 44   b - 44   d ). The tapered sidewalls  4118  of these designs may result in improved manufacturing qualities, e.g., where the frame is molded or stamped and must release cleanly from the tooling. It will be appreciated that illustrating all possible vertical locations for the connecting tab  4116  and taper configurations for the sidewall members  4118  would be impractical, but nonetheless such designs fall within the scope of the current invention, provided that at least one of the sidewall members has a tapered cross-sectional configuration and provided that the connecting tab has a relatively constant vertical thickness T CT  that is significantly smaller than the overall vertical thickness T SW  of the adjacent sidewall members, preferably less than 25% of T SW , more preferably less than 10% of T SW  and sometimes less than 5% of T SW . 
     Referring now to  FIGS. 45   a - 45   f , still further frame designs are illustrated by showing an undivided sidewall  4120  in the same fashion as those of  FIGS. 42   a - 44   e . In these designs, single, double, or multiple connecting tabs  4116  extend between sidewall members  4118  having cross-sectional configurations with single, double or multiple tapers. For example, the sidewall  4120  of  FIG. 45   a  has a single connecting tab and a single direction taper, while the design of  FIG. 45   f  has multiple (i.e., three) connecting tabs and multiple (i.e., six) tapers. Some of the more complex configurations may be unsuited for manufacture by conventional stamping or molding, and must instead be formed using other processes such as extrusion or photo-chemical machining (further described below). It will be appreciated that illustrating all possible cross-sectional configurations for these sidewalls  4120  would be impractical, but nonetheless such designs fall within the scope of the current invention, provided that at least one of the sidewall members has a tapered cross-sectional configuration and provided that each connecting tab has a relatively constant vertical thickness T CT  that is significantly smaller than the overall vertical thickness T SW  of the adjacent sidewall members, preferably less than 25% of T SW , more preferably less than 10% of T SW  and sometimes less than 5% of T SW . 
     Referring now to  FIGS. 46   a - 46   d , portions of several interior sidewalls  4120  are shown in plan (i.e., from above) to better illustrate the configurations of the connecting tabs  4116 . It will be understood that the sidewalls  4120  extend beyond what is shown in the figures to form the complete frame grid. When seen in plan, the paired sidewall members  4118  of an interior sidewall  4120  typically run parallel to one another, but the connecting tabs  4116  may extend continuously between the sidewall members, or they may be intermittent. In addition, the connecting tabs  4116  may be perforated with longitudinal or lateral perforations. For example, in  FIG. 46   a , an interior sidewall (denoted  4120 ′) has a connecting tab  4116  that is a solid piece extending between the two sidewall members  4118 . In this embodiment, the tab  4116  is not continuous everywhere between the sidewall members  4118 , but rather has a fixed length L. Additional similar discrete connecting tabs  4116  may be provided intermittently at other locations between the sidewall members  4118  as required. In contrast, another interior sidewall (denoted  4120 ″) in  FIG. 46   b  has a connecting tab  4116  that extends continuously between the two sidewall members  4118 . In this embodiment, longitudinal perforations  4602  are formed in the connecting tab along each sidewall member to facilitate separation of the sidewall members during singulation. In  FIG. 46   c , a third interior sidewall (denoted  4120 ′″) is shown. The connecting tab  4116  of the sidewall  4120 ′″ has a fixed length L, and it also has longitudinal perforations  4604 , this time formed along the center of the tab to facilitate separation of the sidewall members  4118  during singulation. In  FIG. 46   d , a fourth interior sidewall (denoted  4120 ″″) is shown. The connecting tab  4116  of the sidewall  4120 ″″ has a fixed length L and perforations  4606  formed laterally across the tab from one sidewall member to the other. Solid tabs will preferably be cut apart by laser or by mechanical (e.g., sawing, shearing, etc.) means. Perforated tabs may be cut apart in similar fashion, but may also be separated by twisting or repeated bending along the perforation. 
     Frames for cover assemblies or wafer-level packages, whether for individual or for multiple units, may be fabricated using photo-chemical machining (also known as “PCM”). Photo-chemical machining is a material removal process that uses an etchant (e.g., acid) to “machine” precision parts without cutting. PCM is typically used for forming metal parts, although it can also be used for non-metallic materials (e.g., glasses, semiconductors, ceramics, etc.) with a suitable etchant. Briefly, the silhouette of the desired part is first photographically imaged on a sheet of metal or other material treated with a photo-sensitive resist material. After processing, the unwanted material (i.e., that not protected by the resist material) is etched away, leaving a finished part that duplicates the original silhouette and is stress-free, burr-free and as flat as the parent sheet from which it was etched. Because of certain characteristics of the etching process, the maximum sheet thickness that can be satisfactorily processed using PCM is limited. However, when frames thicker than this maximum sheet thickness are desired, multi-layer frame assemblies may be used as described below. 
     In yet another aspect, multi-layer frame assemblies (also known as laminated frames) are fabricated from a plurality of thin, pre-shaped sheets that are stacked together and bonded into a single unit frame. Each sheet may be pre-formed to have the silhouette of the desired cross section for its respective position in the finished frame, thereby reducing or eliminating the need for further processing after bonding. The sheets may be formed by PCM, stamping, cutting, molding or other known processing methods. The sheets in a multi-layer frame may be made of any of the frame materials disclosed herein. Diffusion bonding (i.e., thermal compression bonding) may be used to laminate the sheets together, as well as other processes such as conventional soldering, brazing, etc. Multi-layer frame assemblies can also be used to fabricate frames having more complex structures, e.g., the flanged frame shown in  FIG. 20   a , by using different silhouettes for different layers. 
     It will be appreciated that the various layers of a multi-layer frame do not necessarily need to be made of the same material. It is only necessary that the materials of directly adjacent sheets be hermetically bondable to one another. Thus, various metals, non-metals, or combinations of metals and non-metals may be laminated together to form a multi-layer frame. Such “mixed-material” laminated frames allow the mechanical, thermal, electrical and/or chemical properties of the frame to be customized. For example, a multi-layer frame can be made with different materials on the upper and lower surfaces to promote bonding to different window and substrate materials. In another example, by laminating sheets of materials having different CTEs, the overall CTE of the resulting multi-layer frame may be customized. 
     Referring now to  FIGS. 47 and 48 , there is illustrated is a multi-layer frame assembly fabricated from sheets made by photo-chemical machining (PCM). While PCM is used for this example, the same general process would be used, with only minor changes, if the sheets were fabricated using the alternative methods previously described.  FIG. 47  shows a plan view of the assembly  4700 , while  FIG. 48  shows a cross-sectional elevation view. The assembly  4700  of this embodiment includes four layers, denoted  4701 ,  4702 ,  4703  and  4704 . Each layer is fabricated by PCM, and includes a plurality of individual frames  4705 , each frame having a continuous sidewall  4706  circumscribing and defining a frame aperture  4708 . It will be understood that the plans of the sidewalls  4706  on each layer  4701 ,  4702 ,  4703  and  4704  of the assembly  4700  will at least partially overlap the plans of sidewalls of the adjacent layers all the way around each of the frame apertures  4708 , and the plan of the uppermost layer  4701  will also substantially correspond to the plan of the frame attachment areas on the window sheet (not shown) to which the frame assembly will be joined. In the embodiment illustrated, the plans of the sidewalls  4706  on each layer  40701 ,  4702 ,  4703  and  4704  are substantially identical, however, such identity of structure is not required for all embodiments (e.g., a flanged frame would have at least some layers with plans that are non-identical). The frame sidewalls  4706  disposed between two frame apertures  4708  in each sheet are held in place by connecting tabs  4710  similar to those shown in  FIGS. 46   a  and  46   c . In this case, however, the connecting tabs  4710  will usually (although not always) have a vertical thickness that is the same as the thickness of the original sheet. To facilitate later singulation, the connecting tabs  4710  for the different layers  4701 ,  4702 ,  4703  and  4704  may be “staggered” to different positions on each layer, thereby minimizing the thickness of any single tab that must be cut. In addition, these connecting tabs  4710  may be solid or perforated as desired. Additional connecting tabs  4712  are used to connect the frame sidewalls  4706  of each layer to an exterior frame  4714 . 
     After PCM machining, the four layers  4701 ,  4702 ,  4703  and  4704  are stacked and joined to one another as described above. The finished frame assembly  4700  may then hermetically joined to a single window sheet and/or to a substrate as previously described to create a multiple-unit cover assembly or a multiple-unit wafer-level package assembly. The completed multiple-unit assembly is later singulated by cutting through the window sheet, connecting tabs and substrate (if applicable) between the individual frame units  4705  to form a plurality of discrete units. Alternatively, rather than bonding the finished frame assembly  4700  to a single window sheet, a plurality of smaller individual window sheets may be placed on top of each individual frame unit  4705  (i.e., one window sheet per frame unit), held in position with appropriate tooling, and hermetically bonded en masse. This eliminates the need to cut through the window sheets during singulation after bonding. In a similar manner, instead of bonding the finished frame assembly  4700  to a single substrate, a plurality of smaller individual substrates (i.e., one substrate per frame unit  4705 ) may be hermetically bonded to the frame assembly  4700  en masse. While these fabrication methods may be used, it will be understood that many of the other fabrication methods and tooling apparatus previously disclosed herein in connection with the hermetic bonding of window assemblies and wafer-level packages may also be applied to PCM frame assemblies. 
     Referring now to  FIG. 49 , shown is a perspective view of a multiple-unit assembly  4900  of PCM-fabricated frames suitable for resistance-seamwelding. It will be noted that the individual frames  4902  are of flanged design, using a flange profile for the bottom PCM layer  4904  and unflanged profile for upper PCM layer(s)  4906 . As previously described, temporary connecting tabs  4908  hold together the individual frame units  4902  for easier material handing and simpler tooling requirements during the process of joining the frame assembly to a single large window sheet, or to multiple smaller window sheets (i.e., one per frame unit  4902 ). 
     In yet another application of this discovery, transparent windowpanes can be hermetically joined to opposite sides of metallic or non-metallic spacers to create hermetically sealed multi-pane thermally insulated window assemblies for residential and commercial buildings, for household appliances and industrial equipment, and for aircraft and other vehicle windows. As in conventional insulated windows, the spacer maintains a gap between adjacent pairs of windowpanes. The space within this gap (i.e., the “gap cavity”) may contain a gas, such as air, nitrogen or argon, or may be a partial vacuum. The contents of the gap cavity reduce the flow of heat through the window, thereby providing thermal insulation. However, conventional insulated windows use either non-hermetic mechanical means (e.g., clamping, gaskets) or non-hermetic adhesives, such as rubber, glues, epoxies and resins, to mount the windowpanes to the spacer. As a result, conventional insulated windows are well known for developing leaks between the gap cavity and the outside environment as they age. In contrast, true hermetically sealed multi-pane insulated window assemblies can maintain their gas-tight integrity indefinitely. 
     Referring now to  FIGS. 50 and 51 , there is illustrated the basic hermetically sealed multi-pane window assembly, namely, a hermetically sealed double-pane window assembly  5000 . It will be understood that the relative dimensions of the assembly  5000  have been exaggerated for purposes of illustration. The hermetic window assembly  5000  includes a transparent upper windowpane  5002 , a transparent lower windowpane  5004 , and a spacer  5006  having a continuous sidewall  5008  that defines a gap cavity  5010  therewithin. The upper windowpane  5002  and spacer  5006  are stacked on the lower windowpane  5004  (as indicated by the arrows in  FIG. 50 ) and then joined or bonded to form a hermetic seal between each windowpane and the spacer. If a particular gas mixture, pressure or other condition is desired for the gap cavity  5010 , it may be introduced prior to, or during the bonding phase of assembly. After bonding, the gap cavity  5010  is hermetically sealed against any transfer of gas to or from the environment. The completed assembly  5000  ( FIG. 51 ) can be used “as is,” or incorporated into higher level assemblies as described below. 
     In some instances, it is desirable or necessary to introduce the desired gas or partial vacuum into the gap cavity  5010  between the windowpanes  5002  and  5004  after the bonding of the windowpanes to the spacer  5006 . To do this, a passage may be formed through the wall  5008  of the spacer  5006  and provided with a valve or pinch-off tube on the outside of the spacer. This may be done before or after bonding. Then, after bonding, the desired atmosphere (including a vacuum or partial vacuum) may be introduced into the gap cavity  5010  through the valve or pinch-off tube. Obviously, if any undesirable gases are left in the gap cavity as a by product of the bonding process, the valve or pinch-off tube may be used to first evacuate them from the gap cavity, and then to introduce the desired gas or atmosphere. Once the gap cavity atmosphere is as desired, the valve or pinch-off tube may be sealed, e.g., by soldering or welding it closed, to preserve the desired long-term hermeticity of the window assembly. 
     The mating surfaces (i.e., the “seal ring areas”) of the windowpanes  5002 ,  5004  and/or of the spacer  5006  may require various preparation or finishing operations prior to the joining operation. Suitable preparations and finishing operations are described herein in detail in connection with window assemblies and wafer-level packages, and therefore will not be repeated. It will however, be understood that such preparation and finishing operations may be applicable to the fabrication of hermetically sealed multi-pane window assemblies. 
     The windowpanes  5002  and  5004  of the hermetic window assembly  5000  will typically be formed of glass, however, other transparent materials may also be used. For example, quartz, silicon, sapphire and other transparent minerals may be used. In certain radiological applications, certain metals, metal alloys and ceramics are considered “transparent” (e.g., to X-rays), so in such applications these materials may also be used for windowpanes  5002  and  5004 . Transparent plastics such as polycarbonate may also be used, however, these materials may allow diffusion of gas through the windowpane itself (as opposed to through the hermetic bond with the spacer) such that a true “hermetically sealed” assembly cannot be maintained indefinitely. 
     Further, while the windowpanes  5002  and  5004  of the hermetic window assembly  5000  will typically be flat in profile (i.e., viewed from the side) and rectangular in shape (i.e., viewed perpendicular to the sheet), this is not required. The windowpanes  5002  and  5004  may be concave, convex or otherwise curved in profile, and each of the windowpanes may have a different profile, as long as each windowpane mates with the spacer  5006  continuously around its entire upper or lower (as the case may be) periphery. In other words, during the bonding process, the respective surfaces of the windowpanes  5002  and  5004  must be in intimate contact with the respective surface of the spacer  5006  to which they are being joined. Similarly, the windowpanes  5002  and  5004  may have any shape, including circular, oval and triangular, providing a correspondingly-shaped spacer  5006  is used. 
     It is envisioned that the spacer  5006  of the hermetic window assembly  5000  will typically be a metal or metal alloy stamping, extrusion, casting or other part fabricated and joined together (if necessary) to continuously surround the gap cavity (it being understood that the spacer itself must hermetically withstand gas diffusion through it to and from the gap cavity). For large window assemblies, especially where cost is a significant consideration, aluminum or aluminum alloys may be used for the spacer  5006 . However, the use of metals or metal alloys for the spacer  5006  is not required, and in some applications, may not even be preferred. Other materials believed suitable for forming the spacer  5006 , include, but are not limited to, glasses, ceramics, composite materials, woven materials encapsulated in composite materials, and materials comprising a combination the materials listed above (including metals and metal alloys). In addition, some or all of the surfaces of the spacer  5006  may be coated or plated to promote bonding to the windowpanes. Suitable coatings are believed to include, but are not limited to glasses, metals, metal alloys, ceramics, composite materials, and woven materials encapsulated in a composite material. 
     It is currently believed that the preferred process for hermetically joining the transparent windowpanes  5002  and  5004  to the spacer  5006  is diffusion bonding. As previously described, diffusion bonding is a process by which a joint can be made between similar or dissimilar metals, alloys, and/or nonmetals by causing the diffusion of atoms across the surface interface. This diffusion is brought about by the application of pressure and heat to the surface interface for a specified length of time. The bonding variables, e.g., temperature, load (i.e., pressure) and time, vary according to the kinds of materials to be joined, the surface finishes, and the expected service conditions. 
     As previously described, a very important characteristic of diffusion bonding is the high quality of the joints produced. Diffusion bonding is the only process known to preserve the properties inherent in monolithic materials, both in metal-to-metal joints and in joints involving non-metals. With properly selected process variables, i.e., temperature, pressing load, and time, the material at the joint (and adjacent thereto) will have the same strength and plasticity as the bulk of the parent material(s). When the process is conducted in vacuum, the mating surfaces are not only protected against further contamination, such as oxidation, but may be cleaned, because the oxides present dissociate, sublime, or dissolve and diffuse into the bulk of the material. A good diffusion bond (sometimes known as a “diffusion weld”) is free from incomplete bonding, oxide inclusions, cold and hot cracks, voids, warpage, loss of alloying elements, etc. If the interfacing surfaces are brought into truly intimate contact, then there is no need for fluxes, electrodes, solders, filler materials, etc. Diffusion-bonded parts typically retain the original values of ultimate tensile strength, angle of bend, impact toughness, vacuum tightness, etc. 
     It is envisioned that in some instances, the bonding process for joining windowpanes  5002  and  5004  to the spacer  5006  will be done in vacuum or partial vacuum (i.e., an evacuated chamber), in partial vacuum with the addition of one or more gases to increase or accelerate reduction of oxides (such as, but not limited to hydrogen), or in partial vacuum with the addition of one or more inert gases such as argon. In other instances, the bonding process will be done in a special atmosphere to increase oxidation of the frame material and/or the glass. This special atmosphere could be a negative pressure, ambient pressure or positive pressure, with one or more gasses added to promote (instead of reduce) the oxidation of the frame material and/or the glass. The added gasses for promoting oxidation include, but are not limited to oxygen. 
     In some instances, it is envisioned that the joint between the windowpanes  5002  and  5004  and the spacer  5006  may include a chemical bond between the spacer material and the windowpane material. This chemical bond may be in addition to a true diffusion bond (i.e., atomic diffusion). In other instances, the chemical bond may be present with little or no evidence of atomic diffusion. 
     For some combinations of materials, surface finishes and process conditions, the diffusion bonding process between windowpanes and spacers in hermetically sealed multi-pane window assemblies may be facilitated by the use of intermediate layers (also known as “interlayers”) of a dissimilar material placed between the windowpanes and the spacer during the diffusion bonding process. The interlayers are believed to act as one or more of the follows: as activators for the mating surfaces; as high ductility interfaces between two less-ductile base materials; as compensators for the stresses arising when a joint involves materials differing in thermal expansion characteristics; as accelerators for mass transfer and/or chemical reactions; as buffers to prevent the formation of undesirable phases in the joint. As previously described, the interlayers may comprise metals, metal alloys, glass materials, solder-glass materials, solder-glass in tape form, solder-glass in sheet form, solder-glass in paste form, paste applied by dispensing or by screen-printing onto either the windowpane or spacer, solder-glass in powder form, glass powder mixed with water, alcohol or another solvent and sprayed, brushed or otherwise applied onto either the interface area of the spacer or the interface area of the windowpane, ceramics, composite materials, woven materials encapsulated in a composite material, or a material composed of a combination of glass and metals and/or metal alloys. 
     After bonding, completed hermetically sealed multi-pane window assemblies may be used in almost all applications where conventional insulated glass windows are used. However, unlike conventional windows, the hermetically sealed window assemblies will not lose their gas-tight integrity. This makes the hermetically sealed window assemblies suitable for premium installations in residential and commercial buildings (e.g., to reduce warranty claims due to fogging or condensation between the panes), in appliances such as ovens, or for use in severe or hazardous environments (e.g., in chemical plants, nuclear plants, outer space, etc.). 
     Referring now to  FIGS. 52 and 53 , there is illustrated a double-hung window unit equipped with a pair of hermetically sealed double-pane window assemblies similar to those shown in  FIGS. 50 and 51 . The double-hung unit  5200  includes upper and lower window frames  5202  and  5204 , respectively, which are slidingly mounted within a frame/rail assembly  5206 . A hermetically sealed double-pane window assembly  5000  is mounted in each window frame  5202  and  5204 . The complete double-hung window unit  5200  ( FIG. 53 ) can be installed into the rough-in frame of a building (not shown) as is a conventional window unit. It will be appreciated that the double-hung window unit is just one example, as hermetically sealed multi-pane window assemblies may also be used for, but not limited to, fixed frame windows, entry door windows, sliding glass doors, casement window assemblies and many other building and construction products. 
     Referring now to  FIGS. 54 and 55 , there is illustrated another hermetically sealed multi-pane window assembly, namely, a hermetically sealed triple-pane window assembly  5400 . It will be understood that the relative dimensions of the assembly  5400  have been exaggerated for purposes of illustration. Similar to the double-pane assembly  5000  previously described, the triple-pane assembly  5400  includes transparent windowpanes  5402  and spacers  5406  having a continuous sidewall  5408  that defines a gap cavity  5410  therewithin. In this embodiment, however, there are three windowpanes  5402  interleaved with two spacers  5406 . Also in this embodiment, the spacers  5406  are provided with pinch-off tubes  5407  connected to passages  5409  through the spacer wall. As previously described, the pinch-off tubes will allow the atmosphere of the gap cavity  5410  to be adjusted after bonding. The upper windowpanes  5402  and the spacers  5406  are stacked on the lower windowpane  5402  (as indicated by the arrows in  FIG. 54 ). The stack is then joined as previously described to form a hermetic seal between each windowpane and the spacer. It will be appreciated that the methods and principles of fabrication for hermetically sealed two- and three-pane window assemblies disclosed herein may be easily extended to allow the fabrication of hermetically sealed window assemblies having 4, 5, 6 . . . n windowpanes interleaved with 3, 4, 5 . . . (n−1) spacers, respectively. 
     Referring now to  FIG. 56 , there is illustrated one apparatus for fixturing multiple sets of window components for simultaneous diffusion bonding, thereby producing multiple hermetically sealed multi-pane insulated window assemblies simultaneously. The fixture apparatus  5600  includes a base  5601  upon which are stacked three sets of windowpanes  5602  and spacers  5606  similar to those described in  FIGS. 50-51 . A hydraulic or pneumatic ram  5608  supplies the pressure (i.e., load) against the top of the stack to press the windowpane and spacer elements together (against the base) during bonding. Separating the adjacent windowpanes (i.e., those belonging to different assemblies) are dividers  5610  formed of a material that will not bond to the windowpanes  5602 , base  5601  or ram  5608  under the expected bonding conditions. The entire fixture apparatus is disposed inside a diffusion bonding chamber (not shown). The diffusion bonding chamber heats the fixture  5600  and its stacked components to bonding temperature, and causes the ram  5608  to apply bonding load (pressure) to the stacked components. The bonding temperature and pressure are maintained for the required bonding time necessary to produce a complete hermetic seal between all of the windowpanes  5602  and their respective spacers  5606 . During the bonding process, the diffusion bonding chamber may be evacuated, pressurized, and/or filled with one or more gases as necessary to be sure the gap cavities of the assemblies have the desired contents, and/or to promote the bonding of the components. After bonding, the three hermetically sealed double-pane insulated window assemblies are complete. Of course, if the assemblies are equipped with valves or pinch-off tubes through the spacers as previously described, then the atmospheres of the gap cavities may still be adjusted as desired before the assemblies are finally hermetically sealed. It will be appreciated that similar apparatus and processes can be use to simultaneously produce large numbers of hermetically sealed multi-pane insulated window assemblies. 
     While diffusion bonding is believed to be the preferred method for joining the windowpanes to the sheets in a hermetically sealed multi-pane window assembly, another bonding apparatus, known as a Hot Isostatic Press (“HIP”) may be used in lieu of the conventional diffusion bonding chamber with internal ram illustrated in  FIG. 56 . A Hot Isostatic Pressing (HIP) unit provides the simultaneous application of heat and high pressure. In the HIP unit a high temperature furnace is enclosed in a pressure vessel. Work pieces (e.g., the window assembly components) are heated and an inert gas, generally argon, applies uniform pressure. The temperature, pressure and process time are all controlled to achieve the optimum material properties. 
     Further, while diffusion bonding is believed preferred, many window-to-frame joining/bonding methods may be used to join the windowpanes to the sheets in a hermetically sealed multi-pane window assembly. These other methods include, but are not limited to, soldering, brazing, welding, electrical resistance heating (ERH), the use of metallization, solder preforms, etc. A large number of suitable methods are described herein in detail in connection with hermetic window assemblies and wafer-level packages, and therefore will not be repeated. It will however, be understood that such window-to-frame joining/bonding processes may be applicable to the fabrication of hermetically sealed multi-pane window assemblies. 
     Preferably, when fabricating hermetically sealed multi-pane insulated window assemblies, the coefficient of (linear) thermal expansion (CTE) of the spacer material(s) is matched as well as possible to the CTE of the associated glass windowpanes. The CTE of most glasses is fairly constant from approximately 273° K (0° Centigrade) up to the softening temperature of the glass. However, some metals and alloys have very different CTEs at different temperatures. Therefore, the average CTE of the spacer material(s) at the elevated glass-to-spacer bonding temperature should be matched as closely as possible to the average CTE of the glass over the same temperature range. The closer the average CTEs of the two materials, the lower will be the residual stresses in the spacer and the glass windowpanes after the assembly cools from the elevated bonding temperature back to ambient (room temperature). 
     The long-term reliability of the spacer-to-glass seal is affected by the degree of matching of the CTEs of the spacer material and the glass for the anticipated end-use environment. For example, if the window assembly is expected to be exposed to temperatures from −40° C. to 100° C. (−40° F. to 212° F.), then the spacer material and the glass material should have closely matched CTEs over this temperature range. If CTE of the spacer material cannot be exactly matched to the CTE of the glass material, then it is desirable that the CTE of the spacer material should be slightly greater than that of the glass. In such case (i.e., where the CTE of the spacer material exceeds that of the glass), the spacer would contract more than the glass during cool-down from the elevated bonding temperature back to ambient, resulting in the glass being in slight compression. This is preferable to the glass being in tension, since glass in tension is prone to cracking. 
     It is thus desirable when designing and fabricating hermetically sealed multi-pane insulated window assemblies to take into consideration data on the ranges of the coefficient of linear thermal expansion (CTE) of metals, metal of alloys and other spacer materials, along with data on the CTE values of glasses and other windowpane materials, so as to ensure the minimum post-bonding stresses, the maximum long-term reliability of the spacer-to-glass seals, and prevention of cracking of the glass windowpanes. 
     This disclosure further describes the attachment of two or more transparent windowpanes to a metallic or non-metallic spacer in order to create hermetic, thermally insulated window assemblies for residential and commercial building construction and other applications. The spacer maintains a gap or space between the pairs of windowpanes. This space may contain a gas, such as nitrogen or argon, or may be a partial or high vacuum. 
     A Vacuum Glazing Unit (VGU) is an Insulating Glass (IG) window unit that contains and maintains a partial vacuum inside the Insulating Glass Unit (IGU). A total vacuum would be the complete absence of any atoms or molecules inside the confined space. A total vacuum is today not practical to produce, so the term “partial vacuum” is used to denote an achievable level of vacuum or significantly reduced amount of atoms and molecules with a defined volume of space. 
     A vacuum-glazing unit (VGU) is a window assembly consisting of, at a minimum, two windowpanes with a space between them and a sealed frame assembly that is joined to the windowpanes and which, together with the windowpanes, defines, contains and maintains a volume of space that holds a practical level of vacuum. The purpose of this type of construction is to produce an IG window unit with the potential for a higher level of thermal insulation that can be obtained my most other constructions of IG units (IGUs). The VGU&#39;s higher level of thermal insulating capability when compared to gas-filled IGUs results from the substitution of the partial vacuum for the fill gas, since a vacuum is known to be the ultimate thermal insulator. Its ultimate insulating value comes from the absence or very low amount of atoms and/or molecules, therefore having very few substances in the volume of the vacuum to mechanically conduct or transfer thermal energy. 
     To make a VGU reliable and practical for installations in the outside-facing (exterior) walls and doors of buildings, the VGU must be able to withstand changes in temperature and barometric pressure, and differences in the building&#39;s inside and outside temperature and barometric pressure. Important factors for long-term insulating performance, reliability and durability of the VGU include the level of hermeticity of the components and assembled VGU, the strength and integrity of the hermetic attachment of the components forming the overall structure of the VGU, and maintaining a practical separation of the VGU&#39;s inside-facing and outside-facing windowpanes. Inside-facing refers to the side of the VGU that faces and is exposed to the inside (interior) of the building structure and outside facing refers to the side of the VGU that faces and is exposed to the outside (exterior) of the building structure. 
     Referring now to  FIG. 57 , there is illustrated a conventional double-pane VGU in accordance with the prior art for purposes of explaining the vocabulary commonly used in the building window industry for the windowpanes of a double-pane VGU, and which will sometimes be used herein. The VGU  5750  includes inner and outer window panes (also called “panes” or “lites”)  5752  and  5754 , respectively. In the industry, the outside pane  5754  is sometimes referred to as window # 1  and the inside pane  5754  is sometimes referred to as window # 2 . A frame  5756  mounts the VGU in the building&#39;s inner and outer walls  5758  and  5760 , respectively, and also maintains separation between the panes  5752  and  5754  to form an insulating gap (also called a “cavity”)  5762 . In the industry, the outside-facing surface of the outside windowpane  5754  is sometimes referred to as surface° # 1 , the inside-facing surface of the outside windowpane is sometimes referred to as surface° # 2 , the outside-facing surface of the inside windowpane  5752  is sometimes referred to as surface° # 3 , and the inside-facing surface of the inside windowpane is sometimes referred to as surface° # 4 . 
     The rate of expansion and contraction of a material per degree change in temperature is called the coefficient of thermal expansion (CTE) or thermal coefficient of expansion (TCE). CTE and TCE are typically expressed as Parts-Per-Million change in dimension per Degree Centigrade or Degree Fahrenheit change in temperature, or abbreviated as PPM/° C. or PPM/° F. 
     In general, the exterior of most buildings will see larger changes in temperature than the interior of the buildings due to daily outside weather changes. Because of this, the outside-facing surface of the VGU (surface # 1 ) will be exposed to greater changes in temperature than the inside-facing surface (surface # 4 ). If both the inside and outside facing windowpane have the same average CTE, the difference in temperature between them will cause the outside-facing windowpane to expand and contract more than the inside-facing windowpane. Any frame or seal mechanism holding the VGU together will have to compensate for the relative dimensional positions of the inside-facing and outside facing windowpanes. If the frame or seal mechanism is not compliant, that is, if it cannot compensate for the difference in location between the perimeters of the two windowpanes, then the bond attaching the frame or seal mechanism to the two windowpanes will incur stresses as a result of the effect of the relative changes in temperature between the inside-facing and outside-facing surfaces of the VGU. It is for this reason that the frame mechanism must be designed and constructed with special features. These features include having the frame member&#39;s CTE closely matched or similar to the windowpane or other item(s) to which it will be attached, and to be compliant in its design and use ductile materials in its construction. By incorporating these attributes, the frame member will be capable of expanding and contracting and thus acting like a spring to compensate for the difference in locations that the items to which the frame member is attached are trying to occupy. 
     Another attribute the frame member of the VGU should have is to be constructed of relatively low thermal conductivity material(s). This is because the frame member will conduct heat from the hotter surface it is attached (bonded, joined) onto, to the cooler surface onto which it has been attached (bonded, joined). Thus minimizing the thermal conductivity of this frame member minimizes the conduction of heat from one windowpane to the other windowpane of the VGU. 
     The preferred method of hermetically attaching the frame members to the windowpanes is by a process called diffusion bonding, a solid-state joining process. This process is also known as thermal-compression bonding (TC bonding). Diffusion bonding is a process by which a joint can be made between similar and dissimilar metals, alloys, and nonmetals, through the action of diffusion of atoms across the interface, brought about by the bonding pressure and heat applied for a specified length of time. The bonding variables (temperature, load and time) vary according to the kind of materials to be joined, surface finish, and the expected service conditions. 
     A very important distinction of diffusion bonding is the high quality of joints. It is the only process known to preserve the properties inherent in monolithic materials, in both metal-to-metal and nonmetal joints. With properly selected process variables (temperature, pressing load, and time), the material at and adjacent to the joint will have the same strength and plasticity as the bulk of the parent material(s). When the process is conducted in vacuum, the mating surfaces are not only protected against further contamination, such as oxidation, but are cleaned, because the oxides present dissociate, sublime, or dissolve and diffuse into the bulk of the material. A diffusion bonded joint is free from incomplete bonding, oxide inclusions, cold and hot cracks, voids, warpage, loss of alloying elements, etc. Since the edges are brought in intimate contact, there is no need for fluxes, electrodes, solders, filler materials, etc. Diffusion-bonded parts usually retain the original values of ultimate tensile strength, angle of bend, impact toughness, vacuum tightness, etc. 
     The bonding process for joining glass and other transparent and semi-transparent materials to a frame material may be done in vacuum or partial vacuum (an evacuated chamber), vacuum with the addition of one or more gases to increase or accelerate reduction of oxides (such as, but not limited to hydrogen), and vacuum with the addition of one or more inert gases such as argon. 
     The bonding process for joining glass to a frame material may be done in a special atmosphere to increase oxidation of the frame material and/or the glass. This special atmosphere could be a negative pressure, ambient pressure or positive pressure, with one or more gasses added to promote (instead of reduce) the oxidation of the frame material and/or the glass. The added gasses for promoting oxidation include, but are not limited to oxygen. 
     In some instances, the bond (joint) resulting from the bonding process will exhibit a chemical bond between the frame/spacer material and the glass. This chemical bond may be in addition to evidence of a diffusion bond (atomic diffusion). In other instances, the bond (joint) will exhibit little or no evidence of atomic diffusion. 
     Composition of the frame members joined to the windowpanes and/or to the internal spacer assembly. The frame members are hermetic structures composed of one or more materials. These materials include, but are not limited to: a glass material; a metal material; a metal alloy material; a ceramic material; composite materials; woven materials encapsulated in a composite material; and a material composed of a combination of two or more of the items listed above. 
     The frame members may be coated or plated to promote bonding (hermetically attaching) two or more frame materials to each other. These materials include, but are not limited to: a glass material; a metal material; a metal alloy material; ceramics; and composite materials. 
     The frame members may be coated or plated to promote bonding to the glass windowpane. These materials include, but are not limited to: a glass material; a metal material; a metal alloy material; a ceramic material; composite materials; woven materials encapsulated in a composite material; and a material composed of a combination of two or more of the items listed above. 
     A typical diffusion bonding process involves holding surface-prepared components together under load (i.e., bonding pressure) at an elevated temperature for a specified length of time. The specific values of the diffusion bonding parameters (i.e., pressure, temperature and time) may vary according to the kind of materials to be joined, their surface finish, and the expected service conditions. Generally speaking, however, the bonding pressures used are typically below those that will cause macrodeformation of the parent materials, and the temperature used is typically less than 80% of the parent material&#39;s melting temperature (in ° K). As previously described, in many cases, diffusion bonding is performed in a protective atmosphere or vacuum, however, this is not always required. 
     Assembly of a VGU with the use of intermediate layers (interlayers) is now described in further detail. The glass-to-frame seal may be made using one or more intermediate layers between the window and the frame assembly during the diffusion bonding process. These intermediate layers are hereafter referred to as interlayers. The interlayers may serve one or more of the following features: as activators for the mating surfaces; sometimes the interlayer material has a higher ductility in comparison to the base materials; as compensators for the stresses arising when a seal involves materials differing in thermal expansion; as accelerators for mass transfer and/or chemical reactions; as buffers to prevent the formation of undesirable phases; or other purposes not mentioned here. The interlayers may comprise: a glass material; a solder-glass material; solder-glass in tape form; solder-glass in sheet form; solder-glass in paste form (e.g., paste would be applied by dispensing or by screen-printing onto either the window component or the frame component); solder-glass in powder form (e.g., the glass powder would be mixed with water, or alcohol or another solvent and sprayed or brushed (painted) onto either the sealing area of the frame or the sealing area of the windowpane); a metal material; a metal alloy material; a material other than glass, glass-solder, metal or metal alloy, including, but not limited to: ceramics; composite materials; woven materials encapsulated in a composite material; or a material comprising a combination of glass and metals and/or metal alloys. 
     It is important to distinguish the use of diffusion bonding interlayers from the use of conventional solder alloys (in perform, paste and other forms) or solder glass (in perform, paste and other forms) and other processes. For purposes of this application, an interlayer is a material used between mating surfaces to promote the diffusion bonding of the surfaces by allowing the respective mating surfaces to diffusion bond to the interlayer or directly to one another. For example, with the proper interlayer material, the diffusion bonding temperature for the joint frame member and the interlayer material, and for the joint between the interlayer material and the windowpane, may be substantially below the diffusion bonding temperature of a joint formed directly between the frame member material and the windowpane material. Thus, use of the interlayer allows diffusion bonding together of the two or three assembly component layers at a temperature that is substantially below the diffusion bonding temperature that would be necessary for bonding those two or three component layer materials directly. The joint, which will preferably be hermetic, is still formed by the diffusion bonding process, i.e., none of the parent materials involved melts during the bonding process and the material of the interlayer diffuses atomically into the parent material. This distinguishes diffusion bonding using interlayers from other processes such as the use of solder alloy (in a variety of forms) or solder glass performs or paste, in which the solder material forms only a surface bond between the materials being joined. It is possible to use materials conventionally used for solders, for example, as interlayers for diffusion bonding. However, when used as interlayers they are used for their diffusion bonding properties and not as conventional solders. 
     The use of interlayers in the production of VGUs or other devices may provide additional advantages over and above their use as promoting diffusion bonding. These advantages include interlayers that serve as activators for the mating surfaces. Sometimes the interlayer materials will have a higher ductility in comparison to the base materials. The interlayers may also compensate for stresses that arise when the seal involves materials having different coefficients of thermal expansion or other thermal expansion properties. The interlayers may also accelerate the mass transfer or chemical reaction between the layers. Finally, the interlayers may serve as buffers to prevent the formation of undesirable chemical or metallic phases in the joint between components. 
     In some embodiments, a variation of diffusion bonding known as Liquid Phase diffusion bonding or sometimes, Transient Liquid Phase diffusion bonding (i.e., “TLP diffusion bonding”) may be used for some or all of the bonds required in the bonded assemblies. In TLP diffusion bonding, solid state diffusional processes caused by the elevated pressure (i.e., load) and heat of the bonding process lead to a change in material composition (e.g., a new material phase) at the bond interface, and the initial bonding temperature is selected as the temperature at which this new phase melts. Alternatively, an interlayer of a material having a lower melting temperature than the parent material may be placed between the layers to be joined, and the initial bonding temperature is selected as the temperature at which the interlayer melts. Thus, a thin layer of liquid spreads along the interface to form a transient joint at a lower temperature than the melting point of either of the parent materials. The initial bonding temperature is then reduced slightly to a secondary temperature allowing solidification of the melt. This elevated temperature (i.e., the secondary temperature) and the elevated pressure (i.e., load) are maintained until the now-solidified transient joint material diffuses into the parent materials by solid-state diffusion, thereby forming a diffusion bond at the junction between the parent materials. 
     Sometimes the interlayer will not be a separate item from the two items to be joined, but rather be a material that has been applied to one or both of the surfaces of the to-be-mated surfaces of the items to be joined together. When the interlayer is pre-applied to one or both mating surfaced, the interlayer may be pre-applied by one of a variety of methods including, but not limited to spray deposition, vapor deposition, plating including solution bath plating, growing the interlayer material onto the to-be-mated item&#39;s surface, painting by brush or roller, and by many other means. 
     It will be appreciated that the terms “diffusion bonding” and “thermal compression bonding” (and its abbreviation “TC bonding”) are often used interchangeably throughout this application and in the art. Metallurgists prefer the term “diffusion bonding”, while the term “thermal compression bonding” is preferred in many industries (e.g., semiconductor manufacturing) to avoid possible confusion with other types of “diffusion” processes used in semiconductor manufacturing. Regardless of which term is used, as previously discussed, diffusion bonding refers to the family of bonding methods using heat, pressure, atmospheres and time alone to create a bond between mating surfaces at a temperature below the normal fusing temperature of either mating surface. In other words, neither mating surface is intentionally melted, and no chemical adhesives are used. 
     The design and materials used for VGUs (and IGUs) can vary. Some variations are shown in  FIGS. 58   a  though  96   c . For purposes of describing these figures, “upper” and “lower” are used to describe the relative position of the components of the VGU instead of “inside”, “inside facing”, “indoor”, “outside”, “outside facing”, “outdoor”, etc. Furthermore, the VGUs are shown illustrated in a horizontal view although they would be installed vertically in most situations, such as when installed in vertical walls and doors. Horizontal installations could include when the VGU is part of a skylight unit on a flat, horizontal portion of a ceiling or floor. It should be further noted that although the descriptions for the items and details in the figures use the terms “upper”, “lower”, “top” and “bottom” to describe the positional relationship of the items and details, the relative relationships of many items could often be reversed, such that the “upper” and “lower” items could be interchanged. Thus, the figures are not intended to imply which side of the VGU would face outdoors and which side would face indoors, or towards a particular direction once installed into the VGU&#39;s next higher assembly. 
       FIGS. 58   a  and  58   b  illustrate the basic concept and components of a vacuum glazing unit (VGU). The VGU  5800  comprises an upper frame member  5810 , bonded to the top surface  5831  of an upper windowpane  5830 . A lower frame member  5890  is bonded to the bottom surface  5873  of the lower windowpane  5870 . Spacers/stand-offs  5840  are applied to the top surface  5871  of the lower windowpane  5870 . These spacers are for the purpose of keeping the upper windowpane  5830  from coming in contact with the lower windowpane  5870 . 
     The frame member  5810  is shown in a side view, cross section form. In its vertical form, it contains at least two radii, shown as upper, inside radius  5815  and lower, outside radius  5817 . These radii provide compliancy to the frame member. 
     The spacers/stand-offs  5840  may be composed of a variety of materials and may be applied to the windowpane surface by a variety of means. These spacers should preferably be made with (composed of) a low thermal conductivity material, since they form a path of thermal conduction between the adjacent surfaces of the two windowpanes. They should outgas very little once included in the assembled and sealed VGU. They should be small enough to not be noticeable under almost any circumstances unless the observer is very close to the VGU. Their numbers and distribution must be sufficient to maintain a mechanical separation of the windowpanes&#39; surfaces  5833  and  5871  from one another under all intended VGU installations. 
     The spacers/stand-offs  5840  may be applied to the surface  5871  of the windowpane  5870  by methods including, but not limited to ink jet dispensing, stencil printing or screen printing, automated pick-and-place equipment where an adhesive might be used to hold the spacers/stand-offs  5840  in place after attachment to the surface  5871  and at least until the VGU is assembled and sealed, or by other means. If ink jet dispensing is used to create the spacers/stand-offs  5840 , each spacers/stand-off may be formed by the application of more than one drop of material. Multiple drops of jetted material could be used to make the desired area of spacer surface  5843  on the windowpane&#39;s surface  5871 . Multiple drops of jetted material could be used to create the desired height of the spacer  5840 . In some embodiments, the spacer&#39;s top surface  5841  is flat, while in other embodiments, the top surface  5841  would be not be flat, but rather would have a radius (be rounded or dome shaped) to minimize the contact area between it and the windowpane surface  5833 . 
     Whenever a spacer is used to maintain separation of two windowpanes, the surface of the windowpane may be treated or coated with a substance to reduce any friction that could result from the relative movement of the spacer to the windowpane as a result of changes in temperature causing changes in the dimension, and thus relative location of the spacer(s) to the windowpane&#39;s surface. Friction where the spacer(s) surface  5841  moved relative to the windowpane&#39;s surface  5833  could result in physical damage (including causing scratches); and/or affect the optical appearance of one or both items; and/or affect the transparency of either or both the spacer(s) and the windowpane. Coatings to reduce friction and/or to reduce or eliminate the possibility of any of the damage described above include chemical vapor deposited diamond (CVD diamond). Additionally, materials such as sheet films could be applied to one or both surfaces ( 5833  and/or  5841 ). 
     Often, IG windows are coated on inside surfaces # 2  and/or # 3  with materials intended to enhance certain features of the IGU. These include low-emissivity (low-e) coatings, and chromatic or chromeric coatings such as electrochromic and polychromic coatings. These and other coatings in use today could also be applied to the inside surfaces # 2  and/or # 3  of the VGUs described herein. 
     Some IGUs are now offered with special coatings applied to the outside surfaces # 1  and/or # 4 . These coatings provide features and functions including making the windows easier to clean. The VGUs described herein could also have windows with these and other coatings applied to outer facing surfaces # 1  and # 4 . 
     Regardless of whether any coatings are applied to surfaces # 1 , # 2 , # 3  or # 4 , if the coatings can withstand the diffusion bonding temperature(s) used to attach the frame member to the windowpane, then the coating may be applied to the windowpane prior to the diffusion bonding process. Should the coating(s) not be able to withstand the diffusion bonding temperature(s) used to attach the frame member to the windowpane, then the coating(s) would have to be applied to the surface(s) of the windowpane after performing the diffusion bonding process. The same would be applicable for any films applied to any surface of either windowpane. 
     Before bonding the frame member and the windowpane together, with or without the use of an interlayer, it may be necessary to remove any pre-applied coatings on the windowpane&#39;s surface where the two items will be joined. Coating removal methods could include chemical removal, mechanical abrasion including sanding or grinding, and/or laser ablation. 
     During the actual diffusion bonding process, the upper bonding surfaces  5811  of upper frame member  5810  are positioned against the top surface  5831  of the upper windowpane  5830 . The bonding surfaces  5811  and the windowpane  5830  are pressed together with sufficient force to produce a predetermined contact pressure between the bonding surfaces and the windowpane along a first junction region, and the junction regions is heated to produce a predetermined temperature along the first junction region. The previous two steps may be conducted simultaneously or in either order, and further may be conducted in a vacuum or special atmosphere. The predetermined contact pressure and the elevated temperature are maintained until a diffusion bond is formed between the upper frame member  5810  and the upper windowpane  5830  around the periphery of the windowpane. 
     Similarly, the top bonding surfaces  5891  of lower frame member  5890  are positioned against the bottom surface  5873  of the lower windowpane  5870 . The bonding surfaces  5891  and the windowpane  5870  are pressed together with sufficient force to produce a predetermined contact pressure between the bonding surfaces and the windowpane along a second junction region, and the junction regions is heated to produce a predetermined temperature along the second junction region. The previous two steps may be conducted simultaneously or in either order, and further may be conducted in a vacuum or special atmosphere. The predetermined contact pressure and the elevated temperature are maintained until a diffusion bond is formed between the lower frame member  5890  and the lower windowpane  5870  around the periphery of the windowpane. 
     Returning now to  FIGS. 58   a  and  58   b , once the frame members are attached to windowpanes and the spacers are applied to the lower windowpane, the unit is ready for final assembly. This entails the hermetic bonding of the lower surface  5813  of the upper frame member  5810 , to the upper surface  5891  of the lower frame member  5893 . 
       FIG. 58   c  points out the top surface  5819  of the upper frame&#39;s bottom edge/flange/foot and the bottom surface  5893  of the lower frame member. Heat can be applied simultaneously to both surfaces  5819  and  5893  to from a hermetic bond or joint that joins the upper frame member to the lower frame member. Heat application methods include electrical resistance seam welding, can welding, and laser welding. Often an additional material is pre-applied to one or both of the surfaces  5813  on the bottom of the upper frame member  5810  and to surface  5891  on the top of the lower frame member prior to bonding the two frame members to each other. One such common material is nickel. When nickel is pre-applied to one or both materials, the joint region is heated to a temperature sufficiently high enough to melt the nickel coating, and the resulting joint is a nickel solder joint. A common method of applying the nickel to the frame member, when the frame is made of a metal or metal alloy material, is to solution bath plate the nickel onto the frame member. Sometimes an additional, very thin metal or metal alloy is subsequently plated or otherwise applied on top or the nickel or other solder material. This is usually done for cosmetic purposed or to help prevent oxidation of the solder material prior to the soldering or brazing process that joins the two frame members together. 
       FIG. 58   d  shows the point of heat application to be at the junction of contact  5899  between the upper and lower frame members. Heat application methods include laser and forced air convection. 
       FIG. 58   e  shows the points of heat application to be at both the locations of  FIG. 58   c  and  FIG. 58   d . This can be accomplished by one of, or a combination of heating methods, including laser, forced-air convection, heater bars (such as is used for hot-bar soldering of electronics), and seam welding where the electrodes contact all three surfaces. 
     In preferred embodiments, the frame members of the VGU are sealed together while in a vacuum environment, thereby “automatically” creating the desired vacuum within the gap, and eliminating the need for a pinch-tube, valve, etc. for evacuation of the VGU gap after it is assembled and sealed. In other embodiments, however, a pinch-tube or valve may be used, and the VGU gap may be evacuated after assembly. 
     While vacuum provides the best insulating properties for multi-pane insulating window assemblies, the physical configuration of the VGUs of the current invention will also benefit multi-pane insulating window assemblies that contain a fill gas or other insulating substances, e.g., aerogels, between the windowpanes. Having a compliant frame assembly that is also hermetically sealed is expected to extend the useful insulating life of these types (i.e., non-vacuum) of windows, too. Some fill gasses, like xenon, are more insulating than krypton, but currently too expensive for most consumers. It is anticipated that when multi-pane insulating window assemblies can be expected to hold an exotic fill gas for 20-50 years, the alternative fill gases would become practical to use. On the other hand, non-gas insulating alternatives such as aerogels may or may not need hermetic encapsulation like vacuum and gas-filled windows. 
       FIG. 58   f  shows a perspective view of one embodiment of a compliant frame member suitable for use in a VGU or IGU such as those described in connection with  FIGS. 58   a - 58   e . The frame  5808  is compliant in all three axes in a side region  5811  below a top flange  5812  and a bottom flange  5814 . The top flange  5812  is adapted for bonding to the top surface of an upper windowpane (e.g., surface  5831  in  FIG. 58   a ), and the bottom flange  5814  is adapted for bonding to the top surface of a lower frame member (e.g., surface  5891  in  FIG. 58   a ). The side region  5811  may incorporate combinations of compliant shapes to provide the necessary multi-dimensional compliance. In the illustrated embodiment, the side region  5811  includes corrugations  5816 , convex recurves  5818  and concave recurves  5820 , however, it will be understood that other configurations are within the scope of the invention. The features of the frame member  5810  in  FIGS. 58   a - 58   e  may correspond to the features of embodiment  5808  as follows: upper bonding surface  5811  ( FIG. 58   a ) may be the reverse side of upper flange  5812  ( FIG. 58   f ); upper radius  5815  ( FIG. 58   a ) may be the reverse side of upper recurve  5818  ( FIG. 58   f ); lower radius  5817  ( FIG. 58   a ) may be the lower recurve  5820  ( FIG. 58   f ); and lower bonding surface  5813  ( FIG. 58   a ) may be the reverse side of lower flange  5814  ( FIG. 58   f ). 
       FIGS. 59   a  and  59   b  show, respectively, an exploded view and an assembled view of a VGU in accordance with another embodiment. The VGU  5900  is generally similar to the VGUs previously described herein, however, it comprises a woven spacer  5950  as further described below. The VGU  5900  further comprises an upper windowpane  5930  having a top surface  5931  and bottom surface  5933 , and a lower windowpane  5970  having a top surface  5971  and a bottom surface  5973 . The woven spacer  5950  includes warp fibers  5953  comprising generally parallel strands of a first fiber/filament interwoven with weft fibers  5955  comprising generally parallel strands of a second fiber/filament running generally perpendicular to the warp. The spacer maintains separation between the inner surfaces  5933  and  5971  of the windowpanes. The VGU  5900  is held together by an upper frame member  5910  and a lower frame member  5990 . The upper frame member  5910  has a top bonding surface  5911  for hermetic bonding to the top surface  5931  of upper windowpane  5930 , an upper inside radius  5915 , a lower outside radius  5917  and a bottom bonding surface  5913 . The lower frame member  5990  includes a top surface  5991  for hermetic bonding to the lower bonding surface  5913  of the upper frame member  5910 , and for hermetic bonding to the bottom surface  5973  of the lower windowpane  5970 . 
     One potential material for the warp fibers/filaments  5953  and weft fibers/filaments  5955  would be glass fiber such as is used for optical fiber. This type of fiber has several benefits, including abundant supply, availability in extremely small diameters, and a fair level of optical transparency. The points where the warp and weft fibers come in contact with each other are higher, taller, and thicker than the diameter of either the warp or weft fibers by themselves. It is these overlapping regions that provide the stand-offs that separate the upper windowpane  5930  from the lower windowpane  5970 . It should be appreciated that employing only parallel warps or wefts between the windowpane surfaces  5933  and  5971  could maintain separation of the two windowpanes, but the surface contact area would be much greater that when using a woven spacer with the appropriate mesh spacing. 
       FIGS. 60   a  and  60   b  show, respectively, an exploded view and an assembled view of a VGU in accordance with another embodiment. The VGU  6000  is generally similar to the VGUs previously described herein, however, it comprises one or more interlayers  6020 ,  6080  and/or  6086  to facilitate diffusion bonding of the frame members and windowpanes. The reasons for using an interlayer are further described herein. 
     The VGU  6000  comprises an upper windowpane  6030  having a top surface  6031  and bottom surface  6033 , and a lower windowpane  6070  having a top surface  6071  and a bottom surface  6073 . A plurality of spacers  6040 , each having a upper surface  6041  and lower surface  6043  are disposed between the inner surfaces  6033  and  6071  of the windowpanes to maintain their separation. The VGU  6000  is held together by an upper frame member  6010  and a lower frame member  6090 . The upper frame member  6010  has a top bonding surface  6011  for hermetic bonding to the top surface  6031  of upper windowpane  6030 , an upper inside radius  6015 , a lower outside radius  6017  and a bottom bonding surface  6013 . The lower frame member  6090  includes a top surface  6091  for hermetic bonding to the lower bonding surface  6013  of the upper frame member  6010 , and for hermetic bonding to the bottom surface  6073  of the lower windowpane  6070 . A first interlayer  6020  having upper surface  6021  and lower surface  6023  may be employed for diffusion bonding purposes between bonding surfaces  6011  and  6031  of the upper frame member  6010  and upper windowpane  6030 , respectively. A second interlayer  6080  having upper surface  6081  and lower surface  6083  may be employed for diffusion bonding purposes between bonding regions  6073  and  6091  of the lower windowpane  6070  and lower frame member  6090 , respectively. A third interlayer  6086  having upper surface  6087  and lower surface  6089  may be employed for diffusion bonding purposes between bonding surfaces  6013  and  6091  of the upper frame member  6010  and lower frame member  6090 , respectively. Use of the interlayers is optional. 
       FIGS. 61   a  and  61   b  show, respectively, an exploded view and an assembled view of a VGU in accordance with another embodiment. The VGU  6100  is generally similar to the VGUs previously described herein, however, it comprises a windowpane that was fabricated to include integral spacers/standoffs that will be used to maintain the separation of the two windowpanes. Having the windowpane produced with integrated spacers mitigates the need for applying individual spacers to one of the windowpanes. The VGU  6100  comprises an upper windowpane  6130  having a top surface  6131  and bottom surface  6133 , and a lower windowpane  6160  having a top surface with integral stand-offs  6161  and a bottom surface  6163 . The integral stand-offs  6161  maintain the separation between the windowpanes. The VGU  6100  is held together by an upper frame member  6110  and a lower frame member  6190 . The upper frame member  6110  has a top bonding surface  6111  for hermetic bonding to the top surface  6131  of upper windowpane  6130 , an upper inside radius  6115 , a lower outside radius  6117  and a bottom bonding surface  6113 . The lower frame member  6190  includes a top surface  6191  for hermetic bonding to the lower bonding surface  6113  of the upper frame member  6110 , and for hermetic bonding to the bottom surface  6163  of the lower windowpane  6160 . Although  FIGS. 61   a  and  61   b  show a VGU with spacers/stand-offs incorporated into the fabrication of the lower windowpane  6160 , it will be appreciated that stand-offs could be fabricated into the upper windowpane, or into both windowpanes, in other embodiments. 
       FIGS. 62   a ,  62   b , and  62   c  illustrate embodiments of a windowpane, similar to the lower windowpane  6160  described in connection with  FIGS. 61   a  and  61   b , having spacers on one of its surfaces that were incorporated into the windowpane&#39;s fabrication. It will be appreciated that stand-offs are not necessarily drawn to scale, thus the proportions and relative spacing of the stand-offs may be different from that illustrated. Windowpane sheet  6260  comprises a substrate having a substantially flat top side  6261  and bottom side  6263 , and a plurality of stand-off features  6265  extend upward from the top surface. In the illustrated embodiment, the stand-offs  6265  have a truncated conical configuration and an evenly arrayed distribution, but in other embodiments the stand-offs may have other configurations and/or distributions. 
       FIGS. 63   a  and  63   b  show, respectively, an exploded view and an assembled view of a VGU in accordance with another embodiment. The VGU  6300  is generally similar to the VGUs previously described herein, however, it comprises a transparent sheet center spacer unit  6350  that is fabricated with spacers/stand-off&#39;s as part of the spacer sheet&#39;s top and bottom sides to enhance the thermal performance (i.e., insulating properties) of the VGU. The spacer sheet with integrated spacers eliminates the need for applying individual spacers to one of the windowpanes. 
     The VGU  6300  comprises an upper windowpane  6330  having a top surface  6331  and bottom surface  6333 , and a lower windowpane  6370  having a top surface  6371  and a bottom surface  6373 . The spacer unit  6350  includes integral stand-offs  6351  on the upper surface, and stand-offs  6353  on the bottom surface. The spacer unit  6350  is placed between the windowpanes  6330  and  6370  to maintain the separation between them. The VGU  6300  is held together by an upper frame member  6310  and a lower frame member  6390 . The upper frame member  6310  has a top bonding surface  6311  for hermetic bonding to the top surface  6331  of upper windowpane  6330 , an upper inside radius  6315 , a lower outside radius  6317  and a bottom bonding surface  6313 . The lower frame member  6390  includes a top surface  6391  for hermetic bonding to the lower bonding surface  6313  of the upper frame member  6310 , and for hermetic bonding to the bottom surface  6373  of the lower windowpane  6370 . Although  FIGS. 63   a  and  63   b  show a VGU with spacers/stand-offs incorporated into the fabrication of both sides of the spacer unit  6350 , in other embodiments, the stand-offs may be incorporated into only the upper or lower surface of the spacer unit. 
     The spacer unit  6350  increases the thermal path of conduction between the upper windowpane  6330  and lower windowpane  6370  when compared to the previously described and employed methods of separating the two windowpanes. The sheet material of this spacer could be composed of glass, plastic sheet or film. The spacer stand-offs  6351  and  6353  could be made from a multitude of materials. As previously discussed, the spacers would preferably be made from a low thermal conductivity material. This spacer unit  6350  may be manufactured as a single piece or may be composed of a sheet or film material with the stand-offs later applied to it by means that include those mentioned previously in the description of the attachment of spacers  5840  for  FIGS. 58   a  and  58   b.    
       FIGS. 64   a  and  64   b  show, respectively, an exploded view and an assembled view of a VGU in accordance with yet another embodiment. The VGU  6400  is generally similar to the VGU  6300  previously described herein, however, it comprises a side shield member disposed between the sealed frame members and the windowpanes. The VGU  6400  comprises an upper windowpane  6430  having a top surface  6431  and bottom surface  6433 , and a lower windowpane  6470  having a top surface  6471  and a bottom surface  6473 . A spacer unit  6450  includes stand-offs  6451  on the upper surface and stand-offs  6453  on the bottom surface. The spacer unit  6450  is placed between the windowpanes  6430  and  6470  to maintain the separation between them. The side shield members  6402  are disposed along the sides of the windowpanes and spacer. The side shield members  6402  preferably have low thermal conductivity. In some embodiments, the shield members may be included for cosmetic purposes, e.g., to conceal the inner frame parts from observation through the windowpanes. In other embodiments, the shield members  6402  comprise “getters” (i.e., gettering material), which absorb or otherwise immobilize stray atoms or molecules in the vacuum space within the VGU. Even if the VGU is hermetically sealed, such atoms or molecules may appear in the vacuum due to out-gassing of one or more of the materials used on or inside the VGU. Such atoms or molecules may also come into the space contained within the VGU by slow penetration through an outside surface (e.g., windowpanes and frame members), through the bonds/joints between frame members and windowpanes and/or through the joint area of the upper and lower frame members. 
     The VGU  6400  is held together by an upper frame member  6410  and a lower frame member  6490 . The upper frame member  6410  has a top bonding surface  6411  for hermetic bonding to the top surface  6431  of upper windowpane  6430 , an upper inside radius  6415 , a lower outside radius  6417  and a bottom bonding surface  6413 . The lower frame member  6490  includes a top surface  6491  for hermetic bonding to the lower bonding surface  6413  of the upper frame member  6410 , and for hermetic bonding to the bottom surface  6473  of the lower windowpane  6470 . 
       FIGS. 65   a  and  65   b  show, respectively, an exploded view and an assembled view of a VGU in accordance with a still further embodiment. The VGU  6500  is generally similar to the VGU  6400  previously described herein, however, it comprises upper and lower frame members that have a similar shape and size. The VGU  6500  comprises an upper windowpane  6530  and a lower windowpane  6570 . A spacer unit  6550  includes stand-offs  6551  on the upper surface and stand-offs  6553  on the bottom surface. The spacer unit  6550  is placed between the windowpanes  6530  and  6570  to maintain the separation between them. Optional side shield members  6502  may be used along the sides of the windowpanes and spacer, however, these are not required. The VGU  6500  is held together by an upper frame member  6510  and a lower frame member  6590 . Preferably, the upper and lower frame members  6510  and  6590  have identical shapes. This results in several advantages, including a reduction in parts count and process steps. The upper frame member  6510  has a top bonding surface  6511  for hermetic bonding to the top surface  6531  of upper windowpane  6530  and a bottom bonding surface  6513 . The lower frame member  6590  includes a top surface  6591  for hermetic bonding to the lower bonding surface  6513  of the upper frame member  6510 , and a bottom bonding surface  6593  for hermetic bonding to the bottom surface  6573  of the lower windowpane  6570 . 
       FIGS. 66   a ,  66   b  and  66   c  show three variations on frame member&#39;s cross-sectional form. Such frame members may be used for upper frame members as illustrated in  FIGS. 58   a - 5   a ,  63   a  and  64   a , or as both upper and lower frame members when symmetrical frame members are used as illustrated in  FIG. 65   a .  FIG. 66   a  shows a frame member  6620  with two radii (denoted  6621  and  6622 ), as has been previously illustrated. Having more than two radii in the vertical component of the frame member may enable the frame member to be more compliant.  FIG. 66   b  shows a frame member  6640  with four radii (denoted  6641 ,  6642 ,  6643  and  6644 ), and  FIG. 66   c  shows a frame member  6660  with six radii (denoted  6661 ,  6662 ,  6663 ,  6664 ,  6665  and  6666 ). 
       FIGS. 67   a  through  67   f  illustrate a muntin assembly suitable for use as the spacer assembly to maintain windowpane separation in a VGU, as well as for cosmetic appearances. Referring first to  FIG. 67   a , there is illustrated a muntin grid unit  6751  comprising a first plurality of parallel muntin bars  6752  disposed perpendicularly to a second plurality of parallel muntin bars  6754 .  FIG. 67   b  illustrates a muntin assembly  6750  comprising the muntin grid unit  6751  and a plurality of spacers/stand-offs  6753  and  6755  (see  FIG. 67   c ) disposed on at least one side surface of the muntin grid unit.  FIG. 67   c  illustrates a side view of the muntin assembly  6750  having stand-offs  6753  and  6755  on both sides.  FIG. 67   d  is an exploded view, in perspective, of the muntin bar assembly  6750  disposed between an upper VGU windowpane  6730  and a lower VGU windowpane  6770 .  FIG. 67   e  is a perspective view of the muntin bar assembly  6750  disposed between, and in contact with the upper windowpane  6730  and the lower windowpane  6770 .  FIG. 67   f  is a side view of the muntin bar assembly  6750  disposed between the upper windowpane  6730  and the lower windowpane  6770 . 
       FIGS. 67   g  and  67   h  show, respectively, an exploded view and an assembled view of a VGU in accordance with yet another embodiment. The VGU  6700  comprises the upper windowpane  6730  having a top surface  6731  and the lower windowpane  6770  having a bottom surface  6773 . The muntin assembly  6750  having stand-offs on the upper and lower surface is disposed between the windowpanes  6730  and  6770  to maintain the separation between them. The VGU  6700  is held together by an upper frame member  6710  and a lower frame member  6790 . The upper frame member  6710  has a top bonding surface  6711  for hermetic bonding to the top surface  6731  of upper windowpane  6730  and a bottom bonding surface  6713 . The lower frame member  6790  includes a top surface  6791  for hermetic bonding to the lower bonding surface  6713  of the upper frame member  6710 , and for hermetic bonding to the bottom surface  6773  of the lower windowpane  6770 . Optionally, interlayers,  6720  and  6780  may be used to facilitate bonding of the upper and lower frame member to the respective windowpanes. 
       FIGS. 68   a  and  68   b  show a VGU  6800  with an internal muntin assembly  6850  and with frame members  6810  and  6890  bonded to the inner (inside) surfaces of the upper and lower windowpanes  6830  and  6870 , respectively. Mounting frame members  6810  and  6890  to the inner (inside) surfaces of the upper and lower windowpanes  6830  and  6870  may be done when there is sufficient space between the two windowpanes to accommodate the thickness of the two frame members. The muntin assembly  6850  illustrated in this embodiment provides the necessary space.  FIG. 68   a  is an exploded view of the VGU with the upper and lower frame members  6810  and  6890  bonded to the inner (inside) surfaces of the windowpanes  6830  and  6870 .  FIG. 68   b  is the assembled VGU with its frame members bonded to the inner (inside) surfaces of the windowpanes. 
       FIGS. 69   a  and  69   b  show a VGU  6900  with an internal muntin assembly  6950  and with inside-the windowpane bonded frame members  6910  and  6990  that extend past (i.e., above and below) the outer surfaces of the upper and lower windowpanes  6930  and  6970 . This is in contrast to  FIGS. 68   a  and  68   b , in which the inside-the windowpane bonded frame members  6810  and  6890  do not extend above or below the outer surfaces of the respective upper and lower windowpanes  6830  and  6870 . 
       FIGS. 70   a  and  70   b  show a VGU  7000  with inside-the-windowpane bonded frame members  7010  and  7090 , similar to those of  FIGS. 68   a  and  68   b . The VGU  7000  includes optional upper and lower interlayers  7020  and  7040  disposed between the respective upper and lower frame members  7010  and  7090  and the respective upper and lower windowpanes  7030  and  7070  to facilitate and/or enhance bonding.  FIG. 70   a  is an exploded view of VGU  7000  with inside-the-windowpane bonded frame members and optional interlayers between the frame members and the windowpanes.  FIG. 70   b  is the assembled view of the VGU. It will be appreciated that the interlayers  7020  and  7040  may or may not actually be visible after bonding, depending upon whether the interlayer material has been completely incorporated into the bond. 
       FIGS. 71   a ,  71   b  and  71   c  illustrate examples of VGUs using an additional, intermediate frame members bonded to the center spacer assembly. In some cases, using these additional frame members provides added benefits to the VGU. Specifically,  FIG. 71   a  illustrates a VGU  7101  comprising upper and lower windowpanes  7130  and  7170 , a center spacer unit  7150 , and upper and lower frame members  7110  and  7190 , similar to that of  FIGS. 63   a  and  63   b.    
       FIG. 71   b  illustrates a VGU  7102 , similar to VGU  7101 , except the spacer unit (now denoted  7150   a ) extends past the sides of the upper windowpane  7130  and lower windowpane  7170 , and the lower frame member (now denoted  7190   a ) has also been extended. This configuration provides the exposed surface area on both the top and bottom of spacer unit  7150   a  to attach center frame member  7140  onto either surface, and provides additional space on the lower frame member  7190   a  to allow bonding of both an extended upper frame member  7120  and the center frame member. In the illustrated embodiment, the center frame member  7140  is shown attached to the top surface of the spacer unit  7150   a , but it may be attached to the bottom surface in other embodiments. 
       FIG. 71   c  illustrates a VGU  7103 , similar to VGU  7102 , except that both the spacer unit  7150   a  and the lower windowpane (now denoted  7170   a ) extend past the sides of the upper window unit  7130 . Again, intermediate frame member  7140  is attached to the top surface of the spacer unit  7150   a.    
       FIGS. 72   a  and  72   b  show, respectively, an exploded view and an assembled view of a VGU in accordance with yet another embodiment. The VGU  7200  is similar to that described in connection with  FIGS. 65   a  and  65   b , except in this embodiment a flat spacer sheet  7250  of transparent material is positioned between the windowpane sheets  7230  and  7270 , and the stand-offs  7255  are built-on to the inner surfaces of the windowpane sheets. The stand-offs  7255  may be formed as an integral part of the windowpanes  7230  and  7270  (e.g., molded on or embossed during manufacturing) or they may be applied to the windowpane separately (e.g., by adhesive) after manufacture of the windowpane. The latter option, i.e., post-manufacture attachment of the stand-offs, allows the inner surfaces of the windowpanes  7230  and  7270  to be coated (e.g., with low-emissivity or other coatings) while still flat, with the stand-offs  7255  being applied after coating. The spacer sheet  7250  may be made of glass, plastic sheets or films, or other transparent materials. The spacer sheet  7250  may be made of a material which inherently has special emissivity, insulating, or other physical properties (e.g., breakage resistance), or it may be coated with other materials to provide the desired properties. The upper and lower frame members  7210  and  7290  are diffusion bonded to the windowpanes  7230  and  7270  as previously described. Optional seal/getter members  7202  may be provided within the package as previously described. 
     It will be appreciated that alternative windowpane shapes may be used. The pairs of windowpanes do not need to be flat. They may be concave or convex in shape. Each of the windowpanes may have a different shape, as long as each windowpane mates intimately with the frame member, e.g., during the bonding process, the surface of glass is in intimate contact with the surface of the frame member to which it is bonded. 
     It will also be appreciated that alternative windowpane materials may be used. The windowpane material need not be glass. It could be a different transparent or non-transparent material, including, but not limited to quartz, sapphire, silicon and even metals, metal alloys, and ceramics. 
     As an alternative to conventional diffusion bonding chambers with internal rams, another apparatus that is suitable for diffusion bonding the windowpanes to the strength-reinforcing layers to form laminated strength-reinforced window assemblies is known as a Hot Isostatic Press (“HIP”). A HIP unit provides the simultaneous application of heat and high pressure. In the HIP unit, the work pieces (e.g., the window assembly components) are typically sealed inside a vacuum-tight bag, which is then evacuated. The bag with work pieces inside is then sealed within a pressure containment vessel or apparatus, which in turn is a part of, or is contained within, a high temperature furnace. A gas, typically argon, is introduced into the vessel around the bagged parts and the furnace turned on. As the furnace heats the pressure vessel, the temperature and pressure of the gas inside simultaneously increase. The gas pressure supplies great force pressing the bagged parts together, and the gas temperature supplies the heat necessary to allow bonding to occur. A HIP unit allows the temperature, pressure and process time to all be controlled to achieve the optimum material properties. 
     In some embodiments, the CTE&#39;s of the materials to be bonded together may be matched. The Coefficient of Linear Thermal Expansion (CTE) of the frame material(s) must be properly matched to the glass windowpanes to which the frame is bonded. The CTE of most glasses is fairly constant from approximately 273° K (0° Centigrade) up to the glass&#39; softening temperature. However, some metals and alloys have different CTEs at different temperatures. 
     The average CTE of the frame material(s) from the elevated glass-to-frame bonding temperature should be closely matched to that of the glass&#39; average CTE over the same temperature range. The closer the average CTEs of the two materials, the lower will be the residual stresses in the frame and the glass windowpanes after the assembly cools from the elevated bonding temperature back to ambient (room temperature). 
     Also critical for long-term reliability of the frame-to glass seal in some embodiments is the close matching of the CTEs of the frame material(s) to the glass for the anticipated end-use environment. For example, if the window assembly is expected to be exposed to temperatures from minus 40° C. to plus 100° C. (minus 40° F. to plus 212° F.) then the frame material(s) and the glass material should have closely matched CTEs over this temperature range. 
     In many embodiments, it is desirable that if CTE of the frame&#39;s material(s) cannot be exactly matched to the CTE of the glass material, then the CTE of the frame&#39;s material(s) should be slightly greater than that of the glass. In this situation where the CTE of the frame material(s) exceeds that of the glass, the frame would contract more than the glass during cool-down from the elevated bonding temperature back to ambient, resulting in the glass being in slight compression. This is preferable to the glass being in tension, since glass in tension is prone to cracking. 
     There are other methods than diffusion bonding that could be employed to attach hermetically the frame member to the windowpane of the VGU. These include: using solder glass, employed primarily between the frame member and the windowpane where the two are to be joined, and then localized or global heating the two parts to form a solder joint; and localized or global heating the two parts to from a fusion joint. Although these and other methods may be used to attach frame members to a windowpane in construction of the described and illustrated VGUs, the preferred method of attachment is diffusion bonding and/or transient liquid phase diffusion bonding. 
     The current invention uses an established, commercially available, technology called diffusion bonding for a proprietary, patent pending application to hermetically join glass windowpanes directly to their compliant (spring-like) metal or metal alloy sleeve/frame component. No glues, adhesives or epoxy materials will be used between the glass and frame component. The attachment will be permanent and more hermetic (gas-tight) than any other attachment method. 
     Referring now to  FIGS. 73   a  and  b , the components of one embodiment of a vacuum-containment IG unit are illustrated,  FIG. 73   a  being an exploded view and  FIG. 73   b  being an assembled view. The IGU  7300  comprises an upper windowpane (i.e., lite)  7330  and a lower windowpane  7370  separated by a transparent spacer unit  7350  disposed therebetween. The edges of the windowpanes  7330  and  7370  are hermetically sealed together using metal or metal alloy frame components  7310  and  7390  as further described below. The cavity between the windowpanes  7330  and  7370  contains a vacuum or partially evacuated atmosphere. 
     Referring now to  FIG. 73   c , one embodiment of the compliant metal frame/sleeve member  7310  and  7390  is shown. It is designed to be flexible in all three axes, allowing the glass lites  7330  and  7390  to expand and contract independently of each other without them or the sleeve-to lite bond region experiencing any significant stresses. Thus it acts similar to an accordion bellows, expanding and contracting as it is pulled and pushed. This sleeve unit can be made to extend very little from the sides of the upper and lower windowpanes. 
     Item  7302  is shown as an optional feature of the IGU  7300 . It is a gettering material, such as is made by SAES Getters. Getters are used in high reliability hermetic packaging to absorb atoms and molecules that are outgased from materials, or to absorb any gas that might leak into the package over an extremely long period of time. 
     The spacer unit  7350  is preferably formed of transparent glass, but may also be formed of transparent polymer materials such as plastics or resins. In certain embodiments described herein, other transparent materials may be used. The spacer unit  7350  comprises a sheet-like substrate portion  7352  having integrally-formed stand-offs (also known as “pillars”)  7354  projecting from one and/or both sides of the substrate portion. The structure may be similar to a plastic chair mat found in offices on the carpet under roller chairs, except that it may have stand-offs on both its top and bottom surfaces. The stand-offs  7354  are disposed generally evenly across the surface of the substrate portion  7352  so as to provide generally even support to the adjacent windowpane. When viewed from above, the stand-offs  7354  will preferably be disposed in an orderly array (see  FIGS. 77-79 ), however, this is not required as long as they provide adequate support to prevent the windowpane from cracking. 
     For purposes of this application, the term “integrally formed” is used to mean that the stand-offs  7354  are formed by manipulating the body of the substrate portion  7352  itself, e.g., by casting, embossing, stamping, etching, etc., rather than by first forming the stand-offs separately from the substrate portion and then attaching them onto the substrate portion later. While the stand-offs  7354  and substrate portion  7352  will generally be composed of the same material when formed, the stand-offs and/or the substrate portion may be further processed, e.g., by heat treatment, chemical treatment, polishing, etc., to modify their characteristics after formation. 
     Referring now to  FIG. 74 , a spacer unit  7450  in accordance with one embodiment is shown. The spacer unit  7450  comprises a transparent sheet-like substrate portion  7452  having integrally-formed stand-offs  7454  projecting from one side. In this embodiment, the unit  7450  is formed of transparent glass, however, other materials may be used in other embodiments. 
     Referring now to  FIG. 75 , a spacer unit  7550  in accordance with another embodiment is shown. The spacer unit  7550  comprises a transparent sheet-like substrate portion  7552  having integrally-formed stand-offs  7554  projecting from both sides of the substrate portion. The unit  7550  is this embodiment is also formed of transparent glass, however, other materials may be used in other embodiments. 
     Referring now to  FIG. 76 , a spacer unit  7650  in accordance with yet another embodiment is shown. In this embodiment, the spacer unit  7650  has a substrate portion formed of multiple discrete layers. A top layer  7655  includes an upper substrate portion  7656  with integral upper stand-offs  7657 , similar to that previously described in  FIG. 74 . A bottom layer  7658  includes a lower substrate portion  7659  with integral lower stand-offs  7660 , also similar to that previously described, although it is not necessary that the top layer  7655  and bottom layer  7658  be formed of the same material. Disposed in a “sandwiched” configuration between the upper and lower substrate portions  7656  and  7659  is a layer of discrete material  7661 . In this embodiment, the top and bottom layers  7655  and  7658  are formed of transparent glass, while the middle layer  7661  is formed of a transparent plastic material such as Lexan. The discrete material layer  7661  may have different thermal conductivity, sound transmission, breakage resistance or other properties than the adjacent layer(s). The discrete material may be a glass, plastic, polymer, resin, adhesive or other material. Its form may be that of a free-standing sheet or film, or it may be a material that is sprayed on or otherwise applied to the free surface (i.e., the one without stand-offs) of one of the substrate portions. It will be appreciated that, while the embodiment shown includes three layers, other embodiments could include only two layers, e.g., only the top layer  7655  and the discrete layer  7661 , or only the bottom layer  7658  and the discrete layer  7661 , or only the top layer  7655  and the bottom layer  7658 . Similarly, multiple discrete internal layers (i.e., without stand-offs) could be used to provide the spacer-unit  7650  with four or more total layers. 
     In some embodiments, performance-enhancing coatings may be “embedded” within the multi-layer laminated spacer  7650 . For example, coatings may be applied to the inner surfaces of the upper substrate portion  7656  and/or lower substrate portion  7659 , or to the surfaces of center layer  7661 . These coatings may include low-emissivity coatings, U-V absorbing or reflecting coatings, color tints, electrochromatic coatings, electrochromeric coatings, anti-reflective coatings and/or other performance-enhancing coatings. After the coatings are applied to the desired surface, the layers of the spacer  7650  are laminated together. In this manner, the coatings, which are often very thin films, are protected from physical damage caused by relative movement between the windowpanes and the spacer. If the same coating was applied to the inside surface of the windowpane, it could be damaged by contact and/or movement of the stand-offs on the spacer unit. 
     Referring again to  FIGS. 74 ,  75  and  76 , performance-enhancing coatings may be applied to either side of the spacer units, e.g., spacer-units  7450 ,  7550 , and  7650 , instead of to the inner surfaces (i.e., surfaces # 2  and # 3 ) of the window panes themselves. These coatings on the spacer unit may include low-emissivity coatings, U-V absorbing or reflecting coatings, color tints, electro-chromatic coatings, anti-reflective coatings and/or other performance-enhancing coatings. In some cases, all coatings will be applied to a single side of the spacer unit, while in other cases selected coatings may be applied on a first side of the spacer unit, and other coatings may be applied to the other side of the spacer unit. In the case of multi-layer spacer units  7650  (e.g.,  FIG. 76 ), coatings may be placed on the free side of the substrate portions and/or on the intermediate layers. 
     Placing the performance-enhancing coatings on the spacer unit  7450 ,  7550  or  7650  may be advantageous because the spacer system (i.e., spacer unit) will often be at a different temperature than either the bulk of window # 1  or window # 2 , and as such, will be expanding and contacting from its center less than window # 1  and more than window # 2 . Having coatings, such as low-e, on the spacer&#39;s substrate surfaces instead of the IG unit&#39;s surfaces # 2  and/or # 3  will eliminate the potential of the coatings being scratched and damaged by the differential movements of the IG Unit&#39;s components. In addition, special coatings may be used to enhance the durability of surfaces # 2  and # 3 , in order to reduce abrasion by the movements of the spacer stand-offs. Coatings such as diamond-like coatings (DLC) will be used to ensure that the glass surfaces remain scratch-free for long periods of time. DLC and other coatings are already in use to provide scratch resistance and resistance to other damage. Another advantage of the proposed spacer system is that the thicker the spacer&#39;s substrate, the greater will be the unit&#39;s thermal resistance, and thus, the overall insulating value of the resulting IG unit. 
     The stand-offs of the spacer unit, e.g., spacer  7450 ,  7550  or  7650  may have cross sections (when seen from above) that are circular, tapered, or of other shapes. Referring now to  FIGS. 77 and 78 , in some embodiments, the stand-offs may have a cross-section (seen from above) resembling a cross or “plus” sign (“+”) to provide the physical separation between the inside surfaces of the IG unit&#39;s windowpanes (surfaces # 2  and # 3 ) and the substrate portion of the spacer unit. In the embodiment shown in  FIG. 77 , the spacer unit  7750  includes a substrate  7752  and a plurality of stand-offs  7754 , all made of glass and integrally formed. The “+” shaped standoffs  7754  have horizontal and vertical members that are about 0.5″ in length, and their wall thickness and height are within the range from about 25 microns to about 50 microns (0.001″ to 0.002″). An average human hair is about 75 microns (0.003″) thick. The extremely small width and height of the glass stand-offs, along with their transparency, will make them practically invisible. In the embodiment shown in  FIG. 78 , the spacer unit  7850  also comprises a substrate  7852  and a plurality of “+” shaped stand-offs  7854 . Both are made of glass, however, in this embodiment, the substrate  7852  is formed as a flat sheet, and then the stand-offs  7854  are affixed onto the substrate later. 
     Referring now to  FIG. 79 , in an alternative embodiment, the spacer unit  7950  comprises stand-offs  7954  having a cross-section resembling the letter “C” that are arranged in an array across the surface of the substrate portion  7952 . The standoffs can be of any shape and size as long as they are strong enough to support the force of the IGU&#39;s windowpanes pressing inward due to the atmospheric pressure&#39;s force on the outside of these two windowpanes. 
     The standoffs must also be strong enough (of adequate material composition and dimensions) so as to retain their size enough that they continue to function as required to keep the two windowpanes from coming into contact with the substrate of the spacer unit, and thus provide a direct thermal path. Also, the standoffs must be designed to have enough surface area so that the static load on the windowpanes they&#39;re supporting does not cause either windowpane to crack, break or otherwise fail. 
     It is desirable to minimize the overall area of contact between the spacer unit and windowpanes in order to minimize the conductive path through the spacer system and maximize the insulating value of the IG unit. However, spacers may experience extremely high loading (pressure) from windows # 2  and # 3  on their surface because the outside of the IG unit is at 14.7 psi (ambient or 1 atmosphere air pressure) while the inside of the unit, with its vacuum, is at near zero psi. Accordingly, the surface area for each stand-off must be selected such that their area loading on the windows # 1  and # 2  would not produce micro-cracks or break the windows, or compress them to a point where they would not be maintaining the separation intended. 
     In one embodiment, IGUs may be assembled as follows: First, the flexible (i.e., compliant) metal sleeves (also called “bellows”) are hermetically bonded to windows # 1  and # 2  to make window sub-assemblies. Next, the spacer system (if used) is placed in between the two window sub-assemblies. Next, the sleeves are hermetically bonded together in a vacuum, so that the entire IG unit is sealed in this vacuum and will not require an evacuation tube and a post-assembly evacuation step. While diffusion bonding is preferred for the hermetic bonding, other methods such as solder glass bonding may be used in some embodiments. 
     Either electrical resistance seam welding or laser welding are among alternatives to hermetically seal the sleeves to each other. A prime consideration for this step is to minimize the heat-affected zone so as not to thermal shock and crack the glass lites. Moderating the heat rate of either process will alleviate this possibility. In addition, copper plates or other material could be placed on the top and bottom surfaces of the unit to act as a heat sink during the sealing process. 
     Referring now to  FIG. 80 , there is illustrated an insulated glass unit (IGU) having a floating spacer unit that maintains separation of the lites (i.e., windowpanes). The IGU  8000  includes lites  8002  and  8004 , which are spaced apart from one another by spacer  8006 . The gap or space  8008  between lites  8002  and  8004  may be filled with a gas or gas mixture or it may contain a vacuum or partial vacuum to yield the desired insulating properties. Flexible sleeves  8010  and  8012  are hermetically bonded to lites  8002  and  8004 , respectively, at one end and are hermetically bonded to one another at the other end to keep the fill-gas or gas mixture (or vacuum) inside the IGU space  8008 . The spacer  8006  is allowed to float, i.e., it is not bonded to both of the lites, although it may be bonded by adhesive or other means to one of the two lites. The position of the spacer  8006  between the two lites  8002  and  8004  is maintained by retaining rods, or bars,  8014  so that it stays in position centered between the two lites. Each retaining bar  8014  is attached to the spacer  8006  at one end and to the flexible sleeves  8010  and/or  8012  at the other end. Preferably, the retaining bar  8014  is attached to the flexible sleeves by crimping therebetween, or other mechanical means, which will not affect the hermetic bond between the sleeves. 
     Referring now to  FIG. 81 , there is illustrated a three-pane IGU in accordance with another embodiment. The IGU  8100  includes lites  8102 ,  8104 , and  8106 . Preferably, the IGU  8100  is gas-filled. Compliant frames (i.e., bellows)  8108 ,  8110 , and  8112  are hermetically bonded to one of the lites at a first end and then bonded to one or both of the other frames at the other end to provide a hermetic seal for maintaining the fill-gas in the sealed spaces  8114  and  8116  between the lites. The IGU  8100  relies on the mechanical strength of the frames  8108 ,  8110 , and  8112  (rather than a spacer) to maintain the desired spacing between the lites. Accordingly, this configuration may be less suitable for use where vacuum levels in spaces  8114  and  8116  and/or compressive loads on the unit are high. 
     Referring now to  FIG. 82 , there is illustrated a three-pane IGU in accordance with another embodiment suitable for use with higher vacuum levels and/or compressive loads than the embodiment shown in  FIG. 81 . The IGU  8200  includes lites  8202 ,  8204 , and  8206 , each attached to a respective compliant frame  8208 ,  8210 , and  8212 . The frames are hermetically bonded to the lites at a first end and to each other at a second end to maintain hermetically sealed spaces  8214  and  8216  between the lites. As in the embodiment described in connection with  FIG. 80 , the spacers  8218  and  8220  float, i.e., they are not bonded to both of the adjacent lites, although they may be bonded to one of the two adjacent lites. In the embodiment illustrated in  FIG. 82 , the spacer  8218  is actually disposed on the inner end of the compliant sleeve  8210 , accordingly, the height of spacer  8218  must be slightly less than the height of spacer  8220  if the spacing between the lites is to be identical. In other embodiments (e.g.,  FIG. 87 ) the spacer may be mounted inside the sleeve bonding area such that the two spacers may have the same thickness. The spacers  8218  and  8220  are held in position by retainer bars  8222  and  8224 , respectively, which extend from the spacers to the compliant frame as previously discussed. It will be noted that the retainer bars  8222  and  8224  are preferably compliant to allow relative movement with the lites. 
     Referring now to  FIG. 83 , the two-lite IGU  8000  of  FIG. 80  is shown from above to illustrate further details. It will be appreciated that, for purposes of illustration, the size of the window-area relative to the frame-area is very small; however, this is to better illustrate details of the frame, and should not be considered a limitation of the invention.  FIG. 83  shows how the lites  8002 ,  8004 , and spacer  8006  are positioned between the compliant frames or sleeves  8010  and  8012 . The compliant frames are hermetically bonded to the glass lites along interior bonding surface  8310  and are bonded to one another along exterior bonding surface  8312 . The floating spacer  8006  is maintained in position by retainer bars  8014 , one or more of which may be mounted along each edge of the spacer. The retainer bar inside end  8314  is attached to the spacer and the retainer bar outside end  8316  extends outward where it may be crimped or otherwise connected to the compliant frames  8010  and/or  8012 . 
     Referring now to  FIG. 84 , there is illustrated a two-pane IGU in accordance with another embodiment. The IGU  8400  is substantially similar to that shown in  FIGS. 80 and 83 . It includes lites  8002  and  8004  disposed on either side of a spacer  8406  to define an interior space  8008 . Compliant frames or sleeves  8010  and  8012  are hermetically bonded to the outside surfaces of the lites at one end and to one another at the other end to hermetically seal the fill-gasses in space  8008 . The spacer unit  8406  differs from the spacer  8006  shown in  FIG. 80  in that the spacer of this embodiment includes internal reinforcement  8408 . In the illustrated embodiment, the reinforcement  8408  comprises an X-shaped internal web, however, other configurations may be used. Preferably, the spacer  8406  is an extruded article having the reinforcement  8408  as an integrally formed part. The retaining bars  8014  of this embodiment have contours designed to make them compliant such that the spacer  8406  may float with respect to the lites  8002  and  8004 . The retaining bar  8014  further includes a connector feature  8410  positioned at the interior end and adapted to connect to the spacer  8406  as further described herein. 
     Referring now to  FIGS. 85 and 86 , an enlarged, cross-sectional view of a portion of the spacer unit  8406  is shown to better illustrate the internal reinforcement and connection aspects of the current invention. The outer wall  8506  of the spacer includes a connector feature  8504  adapted to cooperate with the connector feature  8410  of the retaining bar  8014 . In the illustrated embodiment, the spacer connector feature  8504  comprises a slot  8508  of width “w” formed in the wall  8506  and the retainer bar connector feature  8410  comprises a pair of spaced-apart discs  8510  and  8512  formed on the end of the retainer bar  8014 . The width “w” is selected to be sufficient to accept bar  8014 , but the discs  8510  and  8512  both have a diameter d&gt;w. As best seen in  FIG. 85 , the connector feature  8410  on the retainer bar  8014  can be moved into the connector feature  8508  on the spacer as indicated by arrow  8514 . In the connected configuration shown in  FIG. 86 , the retainer bar  8014  is attached to the spacer  8406  to prevent movement in either direction. 
     Referring now to  FIGS. 87 and 88 , there is illustrated a three-lite IGU having internally bonded frames in accordance with another embodiment. The IGU  8700  includes lites  8702 ,  8704 , and  8706  separated by spacers  8708  and  8710  to form spaces  8712  and  8714 . Compliant frames  8716 ,  8718 , and  8720  are hermetically bonded at one end to the inner surfaces of the lites  8702 ,  8704 , and  8706 , respectively, and to one another at the outer ends to hermetically seal the fill-gas or vacuum in the spaces  8712  and  8714 . Retainer bars  8722  connected between the spacers and frames are used to hold the spacers in place with respect to the lites. 
     In the embodiment illustrated in  FIG. 87 , the spacers  8708  and  8710  are adapted to accommodate the internally bonded frames of IGU  8700 . The upper spacer  8708  is dimensioned to be slightly smaller than the width of the lites, thereby being disposed inwardly of the inner frame ends and avoiding contact with the bonded frame ends. As best seen in  FIG. 88 , the lower spacer  8710  has a stepped configuration within inset portions  8724  on the ends which allow the spacer to avoid contact with the frame ends bonded to the adjacent inner surfaces of the lites  8704  and  8706 . It will be appreciated that the illustrated configurations are only examples, and not limiting. Many other configurations for internally and externally mounting compliant frames will be understood to be within the scope of the invention. 
     Referring now to  FIGS. 89 through 93 , there are illustrated IGUs with holding blocks in accordance with additional embodiments. The holding blocks are adapted to support a significant fraction of the weight of an IGU having flexible sleeves (i.e., frames) when the IGU is mounted vertically in a window or doorframe system. Preferably, the holding block will be configured to minimize contact with the flexible sleeve so as to reduce thermal transfer therebetween. This also allows the sleeve to move as necessary to accommodate relative movement of the window lites. 
     Referring first to  FIG. 89 , there is illustrated a two-lite IGU suitable for use with a holding block. The IGU  8900  comprises lites  8902  and  8904  separated by spacer unit  8906 . In this embodiment, the spacer unit  8906  comprises a transparent sheet  8908  having a plurality of stand-offs  8910  projecting from each side. Compliant frame members  8912  and  8914  are hermetically bonded to the inner surfaces of the lites  8902  and  8904  at a first end  8916 , and hermetically bonded to one another at a second end  8918  to form the hermetically sealed cavity  8920  between the lites. The spacer unit  8906  may be held in position using retainer bars (not shown) as previously described, or using other means described herein. 
     Referring now to  FIG. 90 , there is illustrated the IGU  8900  installed on a holding block. When viewed on end, the holding block  9000  is seen to include a base-portion  9001  and riser portions  9002  and  9004  projecting upwardly from the base portion to define a sleeve cavity  9008 . Each riser portion  9002  and  9004  has a bearing surface  9010  disposed at the upper end. The holding block  9000  is dimensioned such that when the IGU  8900  is positioned on the block, the edges of the lites  8902  and  8904  are supported on the bearing surfaces  9010  of their respective risers  9002  and  9004 , and the compliant sleeves  8912  and  8914  (which are hermetically bonded together) are positioned within the sleeve cavity  9008 . Preferably, the bonded sleeves  8912  and  8914  will not touch the walls of the cavity  9008  so that their movement will not be constrained and so as to minimize thermal transfer. However, a significant fraction (if not all) of the weight of the IGU will be supported by the riser and base portions of the block. The holding block  9000  may be formed of metals such steel or aluminum, but preferably is formed of a non-metal material having lower thermal conductivity, e.g., wood, vinyl, PVC, fiberglass, polyethylene, etc. Although not required, in a preferred embodiment, the holding block  9000  will be formed by extrusion. In other embodiments, rolling, milling, routing or other forming processes may be used to form the holding block. 
     Referring now to  FIG. 91   a , the IGU  8900  and holding block  9000  are illustrated after installation in a channel frame, such as a building window frame or doorframe. The channel frame  9100  includes a base portion  9101  and riser portions  9102  and  9104  projecting upwardly from the base to define a channel  9108 . The channel frame  9100  is dimensioned such that the entire holding block  9000  and a portion of the IGU  8900  fit within the channel  9108 . In this manner, the channel frame  9100  provides both vertical and horizontal support for the IGU  8900 . The channel frame  9100  may be formed of metals such as steel or aluminum, but preferably is formed of a non-metal material having lower thermal conductivity, e.g., wood, vinyl, PVC, fiberglass, polyethylene, etc. 
     It will be appreciated that the channel frame  9100  may be a conventional U-shaped window frame or doorframe. In such cases, the holding block  9000  acts as an adapter to allow the IGU  8900  having external compliant seal frames (e.g., frames  8912  and  8914 ) to be installed in new construction or in an existing structure. 
     Referring now to  FIG. 91   b , it will further be appreciated that in some embodiments, the holding block and the channel frame may be combined into a unitary combine frame. Combined frame  9150  is one example of a unitary frame and holding block. A combined frame may be used in new construction for the support of IGUs (e.g., IGU  8900 ) with external compliant frames without requiring a separate holding block. 
     Referring now to  FIG. 92 , there is illustrated a perspective view of a holding block of one embodiment. The holding block  9200  is substantially similar in cross-section to block  9000  previously described. The block  9200  is preferably formed by extrusion, although other known methods of fabrication may be used. The block  9200  has a length, denoted L, which in some cases may be equal to the length of the associated IGU. In other cases, however, the length L may be only a fraction of the length of the IGU, and multiple blocks  9200  may be disposed along the edge of the IGU for support. 
     Referring now also to  FIG. 93 , to provide additional insulation effect, thermal break slots  9202  may be formed through the base portion  9001  of the holding block  9200 . These slots reduce the cross-sectional area of the material connecting the sides of the block  9200  to reduce heat transfer from one side of the block to the other. 
     Referring now to  FIG. 94   a , there is illustrated a two-pane IGU incorporating anchor spacers in accordance with another embodiment. The IGU  9400  includes panes (i.e., “lites”)  9402  and  9404  separated by a spacer unit  9406  to form a gap cavity  9408 . Compliant frames  9410  and  9412  are hermetically bonded to the interior surface of the panes  9402  and  9404  at one end, and are hermetically bonded together at the other end. Spacer anchors  9414  are provided at each end of the spacer  9406 , extending into the cavity  9416  between the frame members  9410  and  9412 . The spacer anchors  9414  have profile features that trap a portion of the anchor within the compliant frame cavity  9416  when the IGU is assembled. 
     In the illustrated embodiment, the profile features include notched-proximal end  9418 , which accommodates the width of the inner ends of the frames members  9410  and  9412 , and a flared distal end  9420  which has an expanded profile that substantially fills the width between the frame members as they extend from the inner bonding point. It will be appreciated that many other profile features could be used depending on the profiles of the frame members. 
     During assembly of the IGU  9400 , the frame members  9410  and  9412  are first hermetically bonded to their respective panes  9402  and  9404 . Next, the spacer  9406  with anchors  9414  is placed in positioned between the two sub-assemblies. The two window sub-assemblies are then hermetically bonded together along the outer frame joint, thereby trapping the anchors  9414  in place between the frame members  9410  and  9412 . The trapped spacer anchors  9414  prevent the spacer  9406  from moving any significant distance in either direction between the two window panes. 
     The configuration illustrated in  FIG. 94   a  is typical of a gas-filled IGU having an “open” spacer unit  9406  (see, e.g.,  FIG. 83 ). In such IGUs, the pressure differential across the windowpanes is low enough that direct support is not required for the interior portions of the windowpanes. In other embodiments, however, including low pressure IGUs or vacuum IGUs (i.e., VGUs), direct support of the interior portions of the windowpanes is required. In such embodiments, an IGU substantially similar to IGU  9400  may be used, except that the open spacer unit  9406  having spacer anchors  9414  may be replaced with a stand-off type spacer unit (e.g., such as shown in  FIGS. 63   a - 65   a ,  74 - 76  or  89 - 91   a ) having spacer anchors  9414 . The stand-off type spacer is placed between the windowpanes to maintain their separation, and the contoured spacer anchors  9414  are attached to the edges of the spacer to maintain the position of the spacer between the windowpanes by locking into the cavity between the frame members as previously described. 
     Referring now to  FIG. 94   b , there is illustrated an IGU having no spacer at all in accordance with another embodiment. The IGU  9450  includes panes  9452  and  9454 , which are spaced apart from one another to form a gap cavity  9458 . Compliant frames (i.e., bellows)  9460  and  9462  are hermetically bonded to the interior surface of the panes  9452  and  9454  at one end, and are hermetically bonded to each other at the other end. Although compliant, the frames  9460  and  9462  along the sides of the IGU may provide enough mechanical stiffness (or “spring”) to maintain separation of the panes  9452  and  9454  without requiring mechanical spacers. In such cases, a separate spacer unit, whether an open unit disposed around the periphery of the cavity or a stand-off unit disposed between the panes, may not be required. Typically, IGUs not having an internal spacer unit will be gas- or air-filled insulating glass units, since the gas pressure within the cavity  9458  will reduce the differential pressure across the panes, thereby reducing the stiffness required in the frames  9460  and  9462  to maintain separation. 
     Referring now to  FIG. 95 , there is illustrated a three-pane IGU incorporating split anchor spacers in accordance with yet another embodiment. The IGU  9500  includes panes (i.e., “lites”)  9502 ,  9503  and  9504  separated by a spacer units  9506  and  9507  to form a gap cavities  9508  and  9509 . Compliant frames  9510  and  9512  are hermetically bonded to the interior surface of the outer panes  9502  and  9504  at one end, and are hermetically bonded together at the other end. Spacer anchors  9514  are provided at each end of the spacer  9506  and  9507 , extending into the cavity  9516  between the frame members  9510  and  9512 . The spacer anchors  9514  of this embodiment are similar in most ways to the two-pane anchors  9414  previously described. However, the spacer anchors  9514  of this embodiment have different profile features on each side. In particular, when the IGU is assembled, the outward facing surfaces have features  9517  and  9518  that trap a portion of the anchor within the compliant frame cavity  9516 , and the inward facing surfaces have features  9520  that support the center pane  9503 . 
     During assembly of the IGU  9500 , the frame members  9510  and  9512  are first hermetically bonded to their respective outer panes  9502  and  9504  to form outer window sub-assemblies. Next, the spacers  9506  and  9507  with split anchors  9514  are placed on either side of the center pane  9503  to form a center sub-assembly. The center sub-assembly is next positioned between the two outer window sub-assemblies. The two outer window sub-assemblies are then hermetically bonded together along the outer frame joint, thereby trapping the anchors  9514  (with the associated spacers and the center pane) in place between the frame members  9510  and  9512 . The trapped spacer anchors  9514  prevent the spacers  9506  and  9507 , and the center pane  9503 , from moving any significant distance in either direction between the two outer window panes. 
     Referring now to  FIGS. 96   a ,  96   b  and  96   c , there is illustrated an IGU that includes flexible metal sleeves attached to the outside-facing or inside-facing surfaces of glass windowpanes in accordance with yet another embodiment. Whereas the flexible sleeve systems previously described herein have a flexible portion that extends past the outside perimeter of the windowpanes to which they are attached, in this embodiment the flexible components of the IGU are hermetically attached to the inside facing surfaces of the two windowpanes (i.e., industry nomenclature surfaces # 2  and # 3 ), and the flexible portions are “flush” with the outside perimeter, i.e., disposed substantially within the outside perimeter of the IGU. The hermetic attachment may be by diffusion bonding or through the use of solder glass. This configuration may look similar to known gas-filled IGUs that use a spacer along the inside perimeter, however the current embodiment has significant differences. First, the flexible metal spacer is diffusion bonded or attached via solder glass to form a hermetic attachment to the inside-facing surface of each of the two windowpanes. Known IGU systems employ a non-hermetic adhesive or epoxy to bond the spacer unit to the insider of the windowpanes. Second, the spacer in this concept is flexible in all three axes, X, Y and Z, to allow the two windowpanes to expand and contract due to the effects of temperature changes on both sides of the IGU (i.e., inside the wall and outside the wall containing the IGU). When there is significant pressure differential between the inside and outside of the IGU (e.g., when the IGU contains a vacuum or reduced-pressure gas), a transparent spacer system must be used in the IGU to keep the panes mechanically separated. The spacer system also provides the depth required for the flexible sleeves to reside between the windowpanes. 
     Referring now specifically to  FIG. 96   a , in the illustrated embodiment the IGU  9600  comprises an upper lite  9602 , upper flexible frame member  9604 , lower flexible frame member  9606  and lower lite  9608 . It will be appreciated that the frame members  9604  and  9606  are dimensioned to fit within the outside perimeter of the lites, and each frame member has upper and lower bonding surfaces. The outward bonding surface of each of the flexible frame members  9604  and  9606  is hermetically attached to the respective lites  9602  and  9608 , preferably using diffusion bonding or soldering using solder glass, to form a pair of window sub-assemblies  9612  and  9614 . 
     Referring now to  FIG. 96   b , a transparent spacer unit  9610  is placed between the window sub-assemblies  9612  and  9614 . In the illustrated embodiment, the spacer unit  9610  comprises a transparent sheet with an array of stand-offs on each side, however, the spacer units of other embodiments may utilize other configurations previously described herein. The inward bonding surfaces of the two sub-assemblies  9612  and  9614  are next hermetically attached to one another, preferably using diffusion bonding or solder glass, thereby forming a hermetic cavity therebetween and trapping the spacer  9610  within. 
     Referring now to  FIG. 96   c , the completed IGU  9600  is shown. It will be appreciated that the frame members  9604  and  9606  do not extend beyond the periphery of the lites. It will further be appreciated that the desired atmosphere in the cavity of the IGU, e.g., vacuum, reduced-pressure atmosphere or fill-gas, may be placed in the IGU by various methods. First, the bonding of the two sub-assemblies  9612  and  9614  may be performed directly in an appropriate atmosphere (e.g., vacuum, reduced pressure, etc.) such that the desired fill is “trapped” in the cavity at bonding. Alternatively, a pinch-tube or other such port (not shown) may be incorporated into one of the frame members. In this case, the cavity may be evacuated and/or filled with the appropriate fill-gas via the pinch-tube after bonding. The pinch-tube may then be hermetically sealed by known means. 
     It is envisioned that some embodiments of the invention will be insulated glass units having metal sleeves and an electrochromatic or electrochromeric coatings on one or more inside surfaces of the windowpanes. An electrical connection from outside the hermetically sealed unit to the coating on the inside of the unit may be required to control the coating, and in such cases the connection through the metal sleeve must also be hermetic. To maintain hermeticity and also, electrical insulation between the feedthrough wire and the metal frame, a glass-to-metal seal may be used. The use of feedthroughs using glass-to-metal seals is known in the electronic packaging industry. The materials chosen preferably have properties of wettability by glass, matched temperature coefficient of expansion, and low outgassing rates at relevant temperatures, thereby making them suitable for use in vacuum systems. 
     In a still further embodiment, a VGU would comprise an indicator for indicating whether the desired vacuum or reduced pressure atmosphere is still contained within the inter-pane cavity of the VGU, i.e., that the VGU has not developed a leak. One such embodiment includes an indicator disposed in the interior cavity of the VGU, the indicator changing color if the vacuum level decreases and/or outside air enters the cavity. The indicator may be incorporated on a label or other article disposed along the perimeter of the VGU so that it will be visible through the inside windowpane. 
     In yet another embodiment, a gas-filled IGU would comprise an indicator for indicating the integrity of the IGU&#39;s seals, i.e., whether the desired fill-gas had leaked out and/or whether gas has been exchanged between the interior and exterior of the IGU. Preferably, the indicator would comprise a color-changing article such as a label, visible through the inside windowpane. More preferably, a characteristic of the color, e.g., intensity or hue, would indicate the relative magnitude of the leak and/or loss of insulating properties. 
     While the invention has been shown or described in a further variety of its forms, it should be apparent to those skilled in the art that it is not limited to these embodiments, but is susceptible to still further changes without departing from the scope of the invention. 
     In particular, it will be appreciated that the invention may be practiced using various gases, including air, nitrogen, argon, krypton, xenon and mixtures of such gases, to fill the gap between the windowpanes instead of a vacuum. The gases within the gap may be at a reduced or partial pressure, in which case the spacer assemblies described herein may still be necessary, or they may be at ambient or higher pressure, in which case the spacer assemblies described herein may be omitted. In other embodiments, the spacer assemblies described herein may be replaced by simplified spacer assemblies disposed only around the periphery of the windowpanes.