IMPROVED GLASS BONDING MEANS AND METHOD

Abstract: An improved semiconductor die bonding structure and method for electrical devices which utilizes a ductile foil (32) between the semiconductor die (16) and the base of the device package (11). The die is sealed to the foil with an improved die bonding glass material (35) consisting essentially of (by weight percent) 2-10% GeO2, 0-3% SiO2, 62-72% PbO, 0-5% PbF2, 9-12% B2O3, 3-6% Al2O3, 0-5% ZnO, 0.5-2% V2O5, 0-5% CdO, and 4-8% TiO2. The ductile foil (32) is bonded to the ceramic package base (11) directly without intermediate layers or alternatively by means of an improved foil bonding glass material (41) consisting essentially of (by weight percent) 10-15% SiO2, 45-55% PbO, 8-12% ZnO, 2-5% Al2O3, and 25-30% B2O3.

Description: IMPROVED GLASS BONDING MEANS AND METHOD BACKGROUND OF THE INVENTION Field of the Invention This invention relates, in general, to means, methods and materials for mounting electrical devices in packages; and, more particularly, to improved glass compositions, methods, and structures for bonding a semiconductor die to a ceramic base, and to improved semiconductor devices utilizing these materials, methods, and structure. Description of the Prior Art Metal, ceramics, and glasses are commonly used for packaging electrical devices such as semiconductor die in protective enclosures. The semiconductor die may comprise, for example, an individual element such as a diode, resistor, or transistor, an assembly of such elements, or may be an integrated circuit containing hundreds or thousands of elements. The package or protective enclosure can contain one or more semiconductor die and may have from two to a hundred or more external electrical leads. The cerdip package is a common form of semiconductor device package widely used in industry today. It consists, typically, of an alumina ceramic base to which the semiconductor die is bonded, a lead frame for external contacts also bonded to the ceramic base, interconnections coupling the lead frame to the die, and a protective lid over the die and interconnections. Typical ' means used to bond the semiconductor die to the package base are: organic layers (e.g. metal or glass loaded epoxy;) glass layers (e.g. low temperature bonding and/or sealing glasses); or metal layers (e.g. metal layers evaporated on the semiconductor die and screened and fired on the ceramic base, and then alloyed together to fix the die to the base). ' Heat or heat and pressure are common means for for ing the bond. Sometimes the bond is "scrubbed"; that is, the die is moved back and forth laterally in contact with the base, during bonding, in order to achieve a more homogeneous bond region. The physical characteristics of the bond region between the die and base are of great importance since they are a significant factor in determining the thermal impedance between those places in the die where heat is generated and the exterior of the package base from which heat is extracted. Metal layer bonds, because they employ highly conductive materials, generally give lower thermal impedance. However, metal bonding layers use expensive materials and are more complex to make. Thus, devices utilizing them are more expensive. Glass bonding layers are less costly but exhibit higher thermal impedance. Organic bonding layers exhibit still higher thermal impedance. Measurements on a 64 x 64 mil (1.6 x 1.6 mm) silicon semiconductor die bonded to a 16-pin cerdip package base with a gold eutectic metal layer bond gave a junction-to-case thermal impedance ΘJQ of about 20°C per watt. The gold eutectic bond was about 2 mils (51 y thick). The θjς for the same chip and base bonded with a two to three mil (51-76 ym) thick glass layer bond of the prior art was 30-40°C per watt or higher. Type DIP-3, a commercially available bonding/sealing glass manufactured by Kyocera of Kyoto, Japan was used. Attempts to lower the thermal impedance of the glass layer bonded die-package combination by making the prior art glass layer thinner have been unsuccessful. The stress applied to the die due to the thermal expansion and contraction mismatch of the silicon and the alumina base depends on the glass thickness, increasing as the glass thickness decreases. Below about 2 mils (51 ym), the stress exceeds the yield strength of the silicon semicon¬ ductor die and fracture occurs. Thus, with the prior art OMPI glass materials, thinner glass layers have not been practicable and improved ΘJQ of semiconductor devices utilizing glass layer bonded die could not be achieved. Therefore, a need has continued to exist for means, methods, and materials for achieving improved glass layer bonding of the semiconductor die and other components, and for achieving improved electrical devices having lower thermal impedance using glass layer bonding. Accordingly, it is an object of the invention to provide improved bonding and sealing glass compositions for coupling electrical devices, particularly semiconductor die, to package bases. It is a further object of the present invention to provide improved bonding and sealing glass compositions for coupling electrical devices to an intermediate ductile foil which is in turn coupled to a ceramic package base so as to assist in reducing thermal mismatch stress. It is an additional object of the present invention to provide improved bonding and sealing glass compositions for coupling the ductile intermediate foil to the ceramic package base to further reduce thermal expansion mismatch stress. It is a further object of the present invention to provide an improved method for bonding a ductile foil to a ceramic base and, further, a method wherein the foil is substanti l y aluminum. It is an additional object of the invention to provide an improved method for attaching a semiconductor die to a ceramic base. It is a further object of the present invention to provide an improved method for attaching a semiconductor die to a ceramic base using an intermediate ductile foil, sealed with or without use of an intermediate glass layer to the ceramic base, the ductile foil being in turn sealed by another glass layer to the semiconductor die. It is an additional object of the invention to provide an improved semiconductor device using glass layer bonded die and having a lower thermal impedance than the prior art. It is a still further object of the present invention to provide an improved semiconductor device using glass layer bonded die with an intermediate ductile foil for simultaneously achieving stress relief and lower thermal impedance. It is a still further object of the present invention to provide an improved semiconductor device using glass layer bonded die wherein the glass bonding and sealing layer is thinner than has been possible in the prior art. SUMMARY OF THE INVENTION The above and other objects and advantages are achieved in accordance with the present invention wherein there is provided an improved electrical device and package structure comprising a ceramic base, a ductile foil bonded to the base with or without a first bonding/sealing glass region therebetween, a second bonding/sealing glass region in contact with the foil, and an electrical device such as a semiconductor die bonded to the foil by means of the second bonding/sealing glass. There is further provided a manufacturi g method wherein the foil is bonded directly to the ceramic base using heat and pressure exceeding the yield strength of the foil, or in an alternate embodiment by using a first bonding/sealing glass which is substantially alkali-free and which is bonded by heating to a temperature exceeding the glass softening point but less than the melting temperature of the base and foil, and by applying sufficient pressure to plastic or viscous-flow the glass to substantially eliminate voids between the ceramic base and the foil. The die is bonded to the foil by means of a OMPI second bonding/sealing glass of different composition whose softening temperature is less than that of the first glass, and less than the melting temperature of the other materials of the structure. Heat is applied to soften the second glass and pressure provided, with or without "scrubbing" the die, to substantially uniformly distribute the second glass between the die and the foil. Additionally, there is provided a first bonding/sealing glass material having a composition in the range (by weight percent) Si0 2 10-15 PbO 45-55 ZnO 8-12 Al 2 θ3 2-5 B 2 0 3 25-30. Further, there is provided a second bond ng/sealing glass material having a composition in the range (by weight percent) of Ge0 2 2-10 Si0 2 0-3 PbO 62-72 PbF 2 0-5 B 2 θ3 9-12 A1 2 0 3 3-6 ZnO 0-5 CdO 0-5 Ti0 2 4-8. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A shows a top view in simplified form of a cerdip package containing a semiconductor chip. The lid or top of the package has been removed so that the interior details- are visible; OMPI FIG. IB is a side view in simplified form of the cerdip package of FIG. 1A, with the cover included; FIG. 2 shows a cross-section in simplified form, greatly enlarged, of the central section of the package of FIGS. 1A-B according to the prior art; FIG. 3 shows a cross-section in simplified form, greatly enlarged, of the central section of the package of FIGS. 1A-B according to the present invention; FIG. 4 shows a cross-section in simplified form, greatly enlarged, of the central section of the package of FIGS. 1A-B according to an alternative embodiment of the present invention; and FIG. 5 is a plot of thermal impedance as a function of glass thickness. DETAILED DESCRIPTION OF THE DRAWINGS FIGS. 1A-B show, in simplified form, the top view and side view of electrical device 10 which in this case is illustrated as a cerdip package for a semiconductor die. Device 10 includes base 11 which is typically made of a high alumina ceramic and external leads 12 having internal portions 13 lying on base 11. Base 11 contains cavity 15 in which is mounted semiconductor die 16 having connection regions 17. Connection regions 17 are typically electrically connected to internal lead portions 13 of device package 10 by wire bonds (not shown) or similar means well known in the art. In the manufacture of such a device, a lead frame containing lead portions 12 and 13 is mounted on base 11, die 16 is bonded within cavity 15, and wire bonds (not shown) are completed between lead portion 13 and connection regions 17. Cover 14 is attached to base 11 by means of cover sealant 18. FIG. 2 shows, in simplified form, a greatly enlarged cross-section 20 of base 11 of device 10 in the vicinity of cavity 15 according to the prior art. Metallic leads 12-13 OMPI have been omitted for clarity. Cavity 15 has bottom surface 23. Die 16 is mounted in cavity 15 by means of bonding/sealing glass 21 of thickness 25, which bonds face 22 of die 16 to face 23 of base 11. Type DIP-3 glass manufactured by the Kyocera Company of Kyoto, Japan is a typical commercially available prior art die bonding/sealing glass. It has been found that when thickness 25 of bonding glass 21 of the prior art is reduced significantly below 2 mils (51 ym) that die fracture and bond failure result. This comes about because of the mechanical stress which arises due to the differential thermal expansion and contraction of the semiconductor chip relative to the ceramic base. For example, when the semiconductor di e is silicon, which has a linear coefficient of expansion in the range of 23-45 x 10-7 per degree C from room temperature to 500°C_ and the base is a high .alumina ceramic (typically 95% Al 03), which has a linear coefficient of expansion of about 65 x 10~7 p er degree C, the ceramic base shrinks more than the silicon chip as the assembly is cooled from the temperature (about 500°C) at which the glass solidifies. When a thick glass region is used, that is, about two mils (51 ym) or greater, then the force generated by the differential contraction can be readily absorbed, and the stress remains below the yield strength of the silicon and the glass. As the thickness of the glass layer is reduced, however, the same force is distributed, to a first approximation, across the thinner glass region and the stress increases approximately inversely with the glass thickness. Below about 2 mils (51 y ), the stress within the silicon at the boundary between die 16 and glass region 21 exceeds the fracture strength of the silicon and chip fracture results. FIG. 3 shows the same cross section portion 20 of base 11 as in FIG. 2 but with the prior art glass replaced by a means of the present invention. Die 16 is bonded to face 23 of cavity 15 by means of die bonding glass 31 of the present invention and ductile foil 32. Ductile foil 32 has face 34 bonded * to face 23 of cavity 15. Die bonding glass region 31 bonds face 22 of die 16 to face 33 of ductile foil 32. Die bonding glass 31 has thickness 35. Foil 32 has thickness 36. FIG. 4 illustrates an alternate embodiment of the present invention, again showing the same cross section portion 20 of base 11 as in FIGS. 2 and 3. In FIG. 4, die 16 is bonded by means of die bonding glass 31 to ductile foil 32 which is in turn bonded to face 23 of cavity 15 of base 11 by means of foil bonding glass 41. As used in this application, the words "die-glass", "die bonding glass" or "die bonding/sealing glass" are intended to designate glass material region 31 or its equivalent located between die 16 and ductile foil 32. Further, as used in this application, the words "foil-glass", "foil bonding glass" or "foil bonding/'sealing glass" are intended to designate glass material region 41 or its equivalent located between foil 32 and base 11. Glass 31 bonds face 22 of die 16 to face 33 of ductile foil 32. Glass 41 bonds face 34 of ductile foil 32 to face 23 of cavity 15. Ductile foil 32 has thickness 46. Foil bonding glass 41 has thickness 47. Foil bonding glass thickness 47 is typically less than die bonding glass thickness 35. FIG. 5 is a plot of the measured thermal impedance θjς in degrees C per watt as a function of the thickness of die glass region 31, for the die-glass-foil cerdip base configuration shown in FIG. 2, and using the die glass compositions of the present invention, to be discussed later. It will be noted that the thermal impedance for a die glass region thickness of 2 mils (51 ym) is approximately 30°C per watt, comparable to the values typically obtained with prior art glasses of the same thickness. However, as the result of the presence of ductile layer 32, die glass thickness 35 can be reduced to less than one mil (25 y ) without significant die cracking. With such thin die-glass layers, thermal impedance values approaching 20°C per watt are obtained, matching the performance of metal bonding layers. Comparable or better results are obtained using the alternative embodiment of FIG. 4 in which thickness 47 of foil glass region 41 was of the order of 0.1 mil (2.5 ym) or less. Thus the present invention makes possible the use of thinner die glass bonds without cracking and leads to a corresponding improvement in thermal performance. The following is an example of the practice of the method of the present invention in which a silicon semiconductor die is bonded to an alumina cerdip ceramic base. Ductile foil 32 is placed in cavity 15 of base 11 and bonded to lower surface 23 of cavity 15, in a first alternative, by applying only heat and pressure, and in a second alternative, by applying heat and pressure in conjunction with foil bonding/sealing glass 41 between foil 32 and cavity face 23. Aluminum was found to give good results as a ductile foil material and is preferred. The ductile foil must be chosen from that class of materials which has a predetermined melting temperature greater than the temperatures which will be used during the bonding operations or to which the package will be subjected during subsequent processing, and a predetermined yield strength which is less than the yield strength of the semiconductor die, the package base, and the die-glass used in bonding the die to the package base. Other materials which are believed to be useful are, for example, ductile aluminum alloys, gold, silver, copper, and ductile solder alloys. However, aluminum is particularly desirable because it has a relatively high melting point (660°C) and, at the same time, a relatively low yield strength of 3000 psi (21 MPa) and it adheres well to glasses. The ductile aluminum foil is directly bonded to the ceramic.base by applying a pressure significantly exceeding the yield strength. Pressure values of about 14000 psi (97 MPa) at a temperature in the range of 550-650°C were found to give good results. The pressure is applied by means of a hardened steel tool which presses ductile foil 32 against surface 23 of base 11. A thin layer of fine boron nitride powder dusted onto the hardened steel tool prevents it from sticking to the aluminum. Alternatively, foil 32 may be bonded to base 11 by means of thin foil bonding/sealing glass 41 having a specific composition to be described later. Aluminum foil thickness in the range 2-5 mils (51-127 ym) is preferred as giving the best compromise between ease of handling and bonding performance; however, foil of thickness in the range 1-10 mils (25-254 y ) is also useful. Below about 1 mil (25 y ) shear failure of the aluminum foil is more likely. Thickness greater than 10 mils is believed possible, but additional foil thickness increases the thermal path length without further improvement in the bonding properties. Foil bonding/sealing glass 41 can be applied by spraying, painting, screening, spinning or other techniques well known in the art. The glass can be applied either to the package base or the foil. Applying the glass to the foil by spraying was found to be a convenient technique. Only a small amount of glass is required with thicknesses of the order of 0.1 mil (2.5 ym) being useful, and with thinner layers in the vicinity of 0.01 mil (0.25 y ) or less being preferred. The glass-coated aluminum foil was placed in cavity 15 of base 11 and heated to a temperature (e.g. 550-650°C) which exceeded the softening point of the foil-glass but was less than the melting temperature of the foil (660°C) or the ceramic base (about 2000°C). Pressure was applied by means of a steel tool pressing against the upper side of foil 32 so as to to cause glass 41 to flow into a substantially uniform layer to fill the voids and interst'ices of the ceramic surface and accommodate any i nhomogeneities in the surface of the foil. A pressure of 14,000 psi (97 MPa) was found to be convenient, but substantially lower pressures are believed to be useful. With the aluminum foil , it was found to be convenient to use foil-glass compositions having a softening temperature in the range 550-650°C with the range 610-650°C being preferred. In any case, it is essential that the foil bonding/sealing glass have a softening temperature which is less than the melting temperature of the ductile foil and greater than the softening temperature of the die-glass layer which will be subsequently used to bond the die to the foil. It was found, in general, that both direct bonding of the aluminum foil to the ceramic base and glass bonding of the aluminum foil to the ceramic base gave satisfactory results. Glass bonding of the foil to the ceramic base produces a stronger bond, and equal or better thermal characteristics. * Die 16 is attached to foil 32 using a die bonding/sealing glass whose softening temperature is less than the softening temperature of foil bonding/sealing glass 41, and which has filler particles small enough to permit die-glass bond thickness 35 of less than one mil (25 ym) and preferably less than 0.5 mil (13 ym). The composition of such a glass material will be described subsequently. Die-glass thickness as thin as about 0.1 mil (2.5 ym) is believed to be useful. Die bonding/sealing glass 31 may be sprayed, painted, screen printed, spun or applied by other techniques known in the art onto the package or the semiconductor die. It is preferable to apply the die-glass to the semiconductor wafer from which the die is derived prior to separating the wafer into individual die. To effect bonding of the die to the foil , a glass coated die is typically placed in contact with the foil, and heat and pressure applied to soften the glass and seal OMPI it to the foil. A commercial die-bonder (Unitek 8-140) was found to be suitable for this purpose. Other commercially available die-bonders are believed to serve equally well. In a typical run, the heater block temperature of the die bonder was adjusted to 575°C. The cerdip base was placed upon this heater block for about 10-15 seconds in order that the base temperature should rise to a value exceeding the softening point of the die-glass (approximately 530°C). A glass coated die measuring 64 x 64 mils (1.6 x 1.6 mm) was lifted in a die collet and placed on the foil coated base and held in position for approximately two seconds under a force of 70-90 grams and then scrubbed laterally back and forth for approximately ten seconds in order to insure uniform wetting of the surface of the ductile foil by the die bonding/sealing glass, to eliminate voids, and to achieve a substantially uniform glass bonding region between the die and the foil. A useful foil bonding/sealing glass material which is suitable for bonding the ductile aluminum foil to the ceramic base was discovered, which has the following range of compositions of ingredients by weight percent: Si0 2 10-15 PbO 45-55 ZnO 8-12 A1 2 0 3 2-5 B 2 0 3 25-30. range of compositions. A melt was prepared using the following weights of powdered materials in grams: Ingredients Weight in Grams Silica sand (Si0 2 ) 34.6 Lead silicate 379.3 (85% PbO + 15% Si0 2 ) Red Lead (Pb 3 θ4) 38.4 Zinc Oxide (ZNO) 75.0 OMPI Aluminum Hydrate Al (0H) 40.2 Boric Acid (H3BO3) 350.3 The above batch of ingredients was melted in a platinum crucible having a diameter and height of three inches (7.6 cm). The crucible was filled about 80% full and lowered into a laboratory Globar furnace held at 1200°C during the melting and subsequent stirring operations. Following a fifteen minute meltdown of the initial crucible charge, the crucible was removed and additional material was added and the crucible returned to the furnace. This procedure was repeated about four times until all of the batch material had been placed in the crucible. One half hour after the last addition of material, a platinum stirrer having a two inch (5.4 cm) diameter propellor blade was immersed about one inch (2.5 cm) into the molten glass and the melt stirred at 90 rpm for two hours. The crucible was then removed from the furnace and the glass poured into water to produce a glass in "frit" form. The glass frit was removed from the water and dried at about 100° C. The frit was ground in a ball-mill and screened through a 400 mesh stainless steel sieve. It was also found to be convenient to further grind the screened glass powder wet for six to 24 hours. Terpineol, a material well known in the art, was used as the liquid for wet grinding, and for application of the glass. The glass can be applied by methods well known in the art. The glass material made according to the above-described mixing and melting procedure was found to have a density of 4.1 grams per cubic centimeter, a coefficient of thermal expansion of 52 x 10"? per degree C (25-300°C) and a softening/sealing temperature of approximately 600°C. The composition determined after mixing, melting, and cooling is given in the following table in weight percent: Si0 2 12.2 PbO 48.0 ZnO 10.0 A1 2 0 3 3.5 B 2 0 3 26.3 The following die bonding and sealing glass material was found to be useful for the attachment of silicon semiconductor die to aluminum ductile foils and consists essentially ofa composition by weight percent in the range of: Ge0 2 2-10 Si0 2 0-3 PbO 62-72 PbF 2 0-5 B 2 0 3 9-12 A1 2 0 3 3-6 ZnO 0-5 V 2 0 5 0.5-2 CdO 0-5 Ti0 2 4-8. The above composition percentages refer to the composition after the prepared glass has been crushed and diluted with a lead titanate powder. The following are two examples of the preparation of a glass material having a composition within the range specified above. The following batchs of ingredients (in grams) were used to make up die bonding/sealing glasses designated R-233 and R-248. Ingredients Weight in Grams R-233 Glass Germanium Oxide Ge0 10.0 Lead Oxide PbO 634.0 Hammond 75% Red Lead (75%/25%) Pb 3 04/Pb0 50.9 Boric Acid H3BO3 243.3 OMP Aluminum Hydrate Al (0H) 3 105.6 Vanadium Pentoxide V 2 0 5 10.0 R-248 Glass Germanium Oxide Ge0 2 50.0 Lead Silicate (85%/15%) Pb0/Si0 2 133.0 Lead Oxide PbO 554.0 Hammond 75% Red Lead (75%/25%) Pb 3 θ4/PbO 50.9 Lead Fluoride PbF 2 50.0 Boric Acid H 3 B0 3 243.3 Aluminum Hydrate Al (0H) 3 75.0 Zinc Oxide ZnO 50.0 Vanadium Pentoxide V 2 0 5 10.0 Cadmium Oxide CdO 30.0 Each batch was melted in a platinum crucible in a manner similar to that described previously for the foil sealing glass. The raw material was progressively added and melted at 1200°C in a Globar furnace, stirred at 90 rpm for two hours, and then poured into water to produce a glass frit, dried, and then ban-milled and screened through a 400 mesh stainless steel sieve to produce a fine powder. The fine powder was mixed with 20 to 30 volume percent of Perovskite phase lead titanate powder having a particle size less than 8 y and a specific gravity of approximately 7.5. In some cases the glass frit was also ground wet using a Terpineol carrier in the same manner as the foil sealing glass. The die bonding/sealing glass materials prepared as described had a final (after dilution) composition when combined with twenty to thirty volume percent lead titanate as listed in the following table under the headings R-233 and R-248. Prior to dilution with lead titanate the R-233 glass had a density of 6.08 grams per cubic cm, a coefficient of thermal expansion of 87 x 10"? per degree C, and an anneal point of 395°C as measured on a Dupont (Model 900) differential thermal analyzer. When mixed with 20 volume OMF percent lead titante, the glass had a softening/sealing temperature of 530°C and the thermal expansion was lowered to 60 x 10-7 per degree C. By varying the mix of ingredients, the final composition of the glass material could be varied within the general range given above. The following specific glass material compositions were found to be useful : R-233 with 20 R-248 with 20 R-248 with 30 Volume Percent Volume Percent Volume Percent Lead Titanate Lead Titanate Lead Titanate Ge0 2 8.1 4.0 3. 7 Si0 2 1 . 6 1.5 PbO 69.4 63 .1 63.9 PbF 2 4.0 3. 7 B 2 0 3 11.1 11.0 10.0 A1 2 0 3 5.6 3.9 3. 6 ZnO 4.0 3.7 V 2 0 5 .8 .8 . 7 CdO 2.4 2.2 Ti0 2 5.0 5.3 7.0 Coefficient 60 65 59 of Thermal Expansion x 10 7 Bonding/ 530 500 500 Seal ing Temperature in °C The above compositions are given in weight percent. The designations R-233 and R-248 refer to experimental identi¬ fication numbers. All of the above die bonding/sealing glasses were found to give satisfactory results for bonding silicon semiconductor die to ductile aluminum foils bonded in cerdip packages. Thus it is apparent that there has been provided in accordance with this invention, improved glass compositions for sealing ductile foils, particularly aluminum, to - ceramic bases, improved glass compositions for sealing semiconductor die and other components to foils, ceramic bases and enclosures, improved methods for bonding a ductile foil to a ceramic base, improved methods for attaching a semiconductor die to a ceramic base, improved methods and structures for attaching a semiconductor die to a ceramic base using glass bonding/sealing means, and improved semiconductor devices utilizing glass-bonded die wherein the devices have a lower thermal impedance than that obtainable in the prior art of glass die bonding. Having thus described the invention, it will be obvious to those of skill in the art that various modifications can be made within the spirit and scope of the present invention. For example, semiconductor die of materials of other than silicon may be utilized, providing their melting point or decomposition temperature exceeds the softening temperatures of the glass. Other base materials may be utilized besides ceramic, provided their melting or softening temperatures exceed the softening temperatures of the glasses used. Other ductile foil materials besides aluminum may be used provided their yield strength is less than the yield strength of the semicon¬ ductor die, the base, and the glass materials employed, and their melting temperatures exceed the softening temperature of the glasses utilized. It is intended to encompass all such variations as fall within the spirit and scope of the inventi on.

Claims: CLAIMS 1. A sealing glass material consisting essentially of ingredients by weight percentage in the range of: Ge0 2 2- 10 Si 0 2 0-3 PbO 62- 72 P bF 2 0-5 B 2 0 3 9-12 A1 2 0 3 3- 6 ZnO 0- 5 2 0δ 0. 5-2 CdO 0-5 Ti 0 2 4-8. 2. A sealing glass material consisting essentially of ingredients by weight percentage, in the range of: Si0 2 10-15 PbO 45-55 ZnO 8-12 A1 2 0 3 2-5 B 2 0 3 25-30. 3. A method for bonding a ductile foil having a predetermined foil melting temperature to a ceramic base comprising: providing a ceramic base of predetermined base coefficient of expansion and base melting temperature; locating said ductile foil above said ceramic base; placing a substantially alkali-free bonding glass material between said foil and said ceramic base to form an assembly, said bonding glass having a predetermined glass softening temperature less than said foil and base melting temperatures and a predetermined glass coefficient of expansion, wherein said glass coefficient of expansion is smaller, than said base coefficient of expansion; and ^TjR£_ OMPI applying heat and pressure to said assembly, said heat being sufficient to raise the temperature of said assembly so as to be in a range greater than said glass softening temperature, but less than said foil and base melting temperatures, and said pressure being sufficient to cause plastic flow of said glass to substantially eliminate voids between said base and said foil. 4. The method of claim 3 wherein said foil is substan- tially aluminum or ductile aluminum alloys. 5. The method of claim 4 wherein said bonding glass material consisting essentially of ingredients by weight percent in the range of: Si0 2 10-15 PbO 45-55 ZnO 8-12 A1 2 0 3 2-5 B 2 0 3 25-30. 6. A method for attaching a semiconductor die to a ceramic base comprising: locating a ductile foil of a predetermined foil melting temperature and foil yield strength on a portion of said base, said foil yield strength being less than the yield strength of said die and base; bonding said foil to said base by heat and pressure; providing a die-glass coating on said die of predetermined die-glass softening temperature, coefficient of expansion, and yield strength, wherein said die-glass softening temperature is less than said foil melting temperature, and wherein said die-glass yield strength is greater than said foil yield strength; positioning said die and said base so that said die-glass coating on said die contacts said foil; OMP heating and pressing together said base and said die at a temperature exceeding said die-glass softening temperature and less than said foil melting temperature, so as to distribute substantially uniformly and without voids said die-glass between said foil and said die. 7. The method of claim 6 wherein said bonding step further comprises including a foil-glass coating between said foil and said base, heating to a temperature sufficient to permit said foil-glass to flow but less than said foil melting temperature and applying pressure sufficient to spread said foil glass substantially uniformly between said foil and said base, and wherein said foil-glass coating comprises ingredients by weight percent in the range of: Si0 2 10-15 PbO 45-55 ZnO 8-12 A1 2 0 3 2-5 B 2 0 3 25-30. 8. A semiconductor device comprising: a ceramic base having a predetermined ceramic coefficient of expansion, yield strength, and a melting temperature; a ductile foil bonded to at least a portion of said ceramic base, said foil having a predetermined foil yield strength and melting temperature; a die-glass region bonded to at least .a portion of said foil, said die-glass region having a predetermined die-glass coefficient of expansion, yield strength, and softening temperature; a semiconductor die bonded to at least a portion of said die-glass region, said die having predetermined die coefficient of expansion, yield strength, and melting point; .and wherein said foil yield strength is less than said ceramic, die-glass, and die yield strengths, wherein said die-glass coefficient of expansion is intermediate between said ceramic and die coefficients of expansion, and wherein said die-glass softening temperature is less than said die, foil, and ceramic melting temperatures. 9. The device of claim 8 wherein said foil further comprises a foil-glass region between said foil and said base for bonding said foil to said base, said foil-glass having a predetermined foil-glass coefficient of expansion, yield strength, and softening, temperature, and wherein said foil-glass coefficient of expansion is less than said die-glass coefficient of expansion, wherein said foil-glass softening temperature is intermediate between said foil melting temperature and said die-glass softening temperature, and wherein said foil-glass yield strength is greater than said foil yield strength. 10. The device of claim 9 wherein said foil-glass comprises ingredients by weight percent in the range of, Si0 2 10-15 PbO 45-55 ZnO 8-12 A1 2 0 3 2-5 B 2 0 3 25-30; and wherein said die glass comprises ingredients by weight percent in the range of, Ge0 2 2-10 Si0 2 0-3 PbO 62-72 PbF 2 0-5 B 2 0 3 9-12 A1 2 0 3 3-6 ZnO 0-5 V 2 0 5 0.5-2 CdO 0-5 Ti0 2 4-8.

Inventors: DAVIS EARL K, DRYE JAMES E, REED DAVID L, DAVIS, EARL, K., DRYE, JAMES, E., REED, DAVID, L.
Applicants: MOTOROLA INC, MOTOROLA, INC.
Application year: 1982
Main classification: H01L23
IPC codes: C03C3, C03C8, C04B37, H01L21, H01L23