Patent Publication Number: US-7586198-B2

Title: Innerlayer panels and printed wiring boards with embedded fiducials

Description:
RELATED APPLICATIONS 
     This application is related to the application, U.S. Provisional Application Ser. No. 60/418,045, filed in the United States Patent and Trademark Office on Oct. 11, 2002, now converted to U.S. application Ser. No. 10/651,367, filed in the United States Patent and Trademark Office on Aug. 29, 2003 and entitled “CO-FIRED CERAMIC CAPACITORS AND METHOD FOR FORMING CERAMIC CAPACITORS FOR USE IN PRINTED WIRING BOARDS,” the application assigned, U.S. Provisional Application Ser. No. 60/433,105, filed on Dec. 13, 2002, now converted to U.S. application Ser. No. 10/663,551, filed in the United States Patent and Trademark Office on Sep. 16, 2003, and entitled “PRINTED WIRING BOARDS HAVING LOW INDUCTANCE EMBEDDED CAPACITORS AND METHODS OF MAKING SAME,” the application assigned U.S. Application Ser. No. 60/453,129, filed on Mar. 7, 2003, and entitled “PRINTED WIRING BOARDS HAVING CAPACITORS AND METHODS OF MAKING THEREOF,” and the application assigned, U.S. application Ser. No. 10/664,638, filed on Sep. 18, 2003, and entitled “HIGH TOLERANCE EMBEDDED CAPACITORS.” 
     BACKGROUND 
     1. Technical Field 
     The technical field is registration of features in innerlayer printed wiring board panels. More particularly, the technical field includes X-ray alignment of embedded features to their electrical terminations and to other associated circuitry. 
     2. Background Art 
     The practice of embedding passive circuit elements and other features in printed wiring boards (PWB) allows for reduced circuit size, improved circuit performance and for additional semiconductors to be placed on the board surface. Features such as passive circuit elements and other components are typically embedded in panels that are stacked and connected by interconnection circuitry, the stack of panels forming the printed wiring board. The panels can be generally referred to as “innerlayer panels.” 
     Passive circuit elements can be fabricated by a number of methods. “Formed-on-foil” elements such as resistors, for example, are formed by selectively depositing a thick-film resistor material on a metallic foil. Capacitors are formed on foil by depositing a thick-film dielectric and conductor combination. Such elements can be fired under thick-film firing conditions or cured at low temperatures. The resultant passive elements are then laminated to a dielectric and to a second foil, forming an innerlayer panel. The foils are disposed on the exterior of the innerlayer panel, and are used to form circuitry. 
     A printed wiring board is formed by photo-etching the foils on the exterior of the innerlayer panel to create circuitry, and then stacking and laminating the panels. The circuitry must be accurately positioned on the innerlayer panel in order to properly interconnect circuitry of the stacked panels in the printed wiring board. The circuitry is formed by punching register holes at specific locations in each innerlayer panel, and using register pins to position a photo-tool. The photo-tool is used to image circuitry on the exterior of the panels. The circuitry of the innerlayer panels is thereby correctly aligned during lamination. 
     Embedded circuitry, components and other features in an innerlayer panel must also be accurately interconnected to the circuitry on the exterior of the innerlayer panel. The alignment process is difficult, however, because embedded features are not visible. One alignment process involves the use of fiducials as position locators in an innerlayer panel. The fiducials are printed on a foil at the same time as embedded features during formation of the panel. Regions of the foil containing the fiducials are selectively etched away in the vicinity of the fiducials in order to expose the fiducials. Register holes are then punched in the innerlayer panel in known positions relative to the now visible fiducials. The register holes are used to position a photo-tool for further etching of the foil, which results in circuitry on the exterior of the panel. 
     Etching away the foil to expose fiducials allows for alignment of embedded features with other circuitry of the innerlayer panel. The etching processes, however, add time and cost to the alignment process. 
     SUMMARY 
     According to a first embodiment, a method of making an innerlayer panel comprises forming features and fiducials over a metallic foil. The locations of the fiducials are used to align embedded features with circuitry of the innerlayer panel. X-rays are used to determine the locations of the fiducials, which are distinguishable through the metallic foil. In one embodiment, the fiducials are formed from a thick-film paste containing a high-density element such as tungsten. 
     According to the first embodiment, embedded features can be accurately aligned to circuitry when constructing a printed wiring board. Because the locations of the fiducials can be determined using X-rays, there is no requirement for etching back parts of the innerlayer panel to expose the fiducials. 
     Those skilled in the art will appreciate the above stated advantages of the invention upon reading the following detailed description of the embodiments with reference to the below-listed drawings. 
     According to common practice, the various features of the drawings discussed below are not necessarily drawn to scale. Dimensions of various features and elements in the drawings may be expanded or reduced to more clearly illustrate the embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a top plan view of a first stage of manufacture of an innerlayer panel according to a first embodiment; 
         FIG. 1B  is a section view in front elevation taken on line  1 B- 1 B in  FIG. 1A ; 
         FIG. 1C  is a section view in front elevation of a second stage of manufacture of an innerlayer panel according to the first embodiment; 
         FIG. 1D  illustrates an X-ray image of fiducials obtained during manufacture of the first embodiment; 
         FIG. 1E  illustrates punched register holes in the innerlayer panel during manufacture of the first embodiment; 
         FIG. 1F  is a section view in front elevation of a completed innerlayer panel, before incorporation into a printed wiring board; and 
         FIG. 2  is a section view in front elevation of a portion of a printed wiring board. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention are directed to methods of making innerlayer panels and methods of forming printed wiring boards from the innerlayer panels. The innerlayer panels include fiducials that are used to align electrical terminations and associated circuitry with embedded features. The features can be, for example, formed-on-foil elements and embedded components or circuitry in the printed wiring board. The fiducials can be of a shape and density such that they are identifiable through the metallic foils of an innerlayer panel using X-rays. 
     According to a first embodiment, an innerlayer panel is formed by printing fiducials over a metallic foil using a paste containing a high-density material. The fiducials may be printed before or after the embedded features are printed on the foil. The locations of the high-density paste fiducials can be identified through the metallic foil using X-rays. A method of making an innerlayer panel according to the first embodiment is described below with reference to  FIGS. 1A-1E . 
       FIG. 1A  is a top plan view of a first stage of manufacture of an innerlayer panel.  FIG. 1B  is a section view taken on line  1 B- 1 B in  FIG. 1A . In  FIGS. 1A and 1B , a metallic foil  10  is provided. The foil  10  may be of a type generally available in the industry. For example, the foil  10  may be copper, copper-invar-copper, invar, nickel, nickel-coated copper, or other metals. Preferred foils include foils comprised predominantly of copper, such as, for example, reverse-treated copper foils, double-treated copper foils, and other copper foils commonly used in the multilayer printed circuit board industry. The thickness of the foil  10  may be in the range of, for example, about 1-100 microns, preferably 3-75 microns, and most preferably 12-36 microns, corresponding to between about ⅓ oz and 1 oz copper foil. 
     Fiducials  20  are formed over the foil  10 . The fiducials  20  can be formed by, for example, screen-printing. The fiducials  20  are formed such that they are discernible through the metallic foils of the innerlayer panel using X-rays. The fiducials  20  can be formed in one or more screen-printing steps. Examples of dimensions and thicknesses for the fiducials  20  are discussed in detail below in Examples 1-4. 
     Next, features  12  are formed over the foil  10  in known positions with reference to the positions of the fiducials  20 . The features  12  illustrated in  FIGS. 1A and 1B  are resistors, but any other forms of circuitry or components can be formed over the foil  10  according to the principles of the present invention. For example, passive circuit elements such as capacitors may also be formed over the foil  10 . If the features  12  are resistors, the resistors  12  can be formed by, for example, screen-printing a thick-film paste such as is known in the art. If capacitors are formed, the foil  10  can be used to form a first electrode, and additional dielectric and conductive layers can be formed over the foil  10  using known processes and materials. Other features can also be formed over the foil  10 . 
     The resulting article is then fired under thick-film firing conditions. The fiducials  20  and the features  12  can be fired at the same time or in separate steps. Encapsulant  25  may be formed over the features  12  and the fiducials  20  after firing. The encapsulant  25  serves to protect the fiducials  20  from the black oxide process. The black oxide process is an acid chemical process that causes copper to oxidize and create an oxide surface film. When a copper foil  10  is used, the oxide surface film improves adhesion of the foil  10  to epoxy prepreg during lamination. The black oxide process, however, can dissolve metals such as tungsten, which may be used in certain embodiments of the fiducials  20 . The encapsulant can be an organic system, such as epoxy, that can be printed over the fiducials and cured at temperatures between 100° C. and 200° C. to achieve desired properties. The encapsulant can also be a thick-film glass composition, where its properties are achieved by firing under thick-film firing conditions. The same encapsulant  25  can be used to print over the features  12  and the fiducials  20 , and the features  12  can be encapsulated in a single printing. 
       FIG. 1C  is a section view of the next stage of manufacture. Referring to  FIG. 1C , the resulting article is laminated to a dielectric material  30 . In  FIG. 1C , the component face side of the foil  10  is laminated to the dielectric material  30 . The lamination can be performed, for example, using FR4 prepreg in standard printing wiring board processes. For example,  106  epoxy prepreg may be used. Suitable lamination conditions are 185° C. at 208 psig for 1 hour in a vacuum chamber evacuated to 28 inches of mercury. A silicone rubber press pad and a smooth PTFE filled glass release sheet may be in contact with the foil  10  to prevent the epoxy from gluing the lamination plates together. A metallic foil  40  may be applied to the laminate material  30  to provide a second surface for creating circuitry. 
     After lamination, the resulting article is transferred to an X-ray drill machine. The X-ray drill machine locates the fiducials  20  using X-rays.  FIG. 1D  generally illustrates the image obtained by X-raying the laminate article. The fiducials  20  may be of such shape, size and density so that X-rays can be used to detect them through the foils  10  or  40 . The features  12  do not have a density that is sufficiently different from the metallic foils  10  or  40  to be visible in the X-ray image. 
       FIG. 1E  illustrates the formation of register holes  35  in the laminate article. The locations of the fiducials  20  are used to position the laminate article so that the register holes  35  may be formed in known positions relative to any features embedded in the laminate article. The register holes  35  may be formed by, for example, drilling or punching. 
       FIG. 1F  is a section view of the laminate article after etching the foils  10 ,  40  (reference numbers  10  and  40  are not used in  FIG. 1E ). An innerlayer panel  100  results from the etching process. Terminations  50  are formed from the foil  10 , and additional circuitry  42  is formed from the foil  40 . In forming the terminations  50  and the circuitry  42 , a photo-resist is applied to the foils  10 ,  40  and the foils  10 ,  40  are imaged, developed, etched and stripped using standard printing wiring board processing conditions. A photo-tool is used to image the foils  10 ,  40 . The photo-tool is aligned using the register holes  35  along with register pins. The alignment step ensures that the imaging process and the subsequent etching process result in component foil terminations  50  and associated circuitry that are accurately aligned with the features  12 . 
     According to the above embodiment, there is no need for etching steps to expose the fiducials  20 , as is required in known alignment methods. 
       FIG. 2  illustrates a sectional view in front elevation of a portion of a printed wiring board  1000 . The printed wiring board  1000  includes an innerlayer panel  1100  and additional innerlayer panels  1200 ,  1300  . . . . . The innerlayer panel  1100  is a schematic representation of the innerlayer panel  100  illustrated in  FIG. 1E , after incorporation of the innerlayer panel  100  into the printed wiring board  1000 . The printed wiring board  1000  may also include a power plane and a ground plane (not illustrated). An exemplary device D is shown as coupled to the connection circuitry  1021 ,  1022 . The device D can be, for example, a semiconductor chip. The connection circuitry  1021 ,  1022  is also connected to a feature  12 , which may represent any of the features  12  of the innerlayer panel  100 . The feature  12  can be, for example, a capacitor coupled to the device D. 
     The innerlayer panels used to form the printed wiring board  1000  can be laminated together in a lamination pressing. The register holes  35  (shown in  FIG. 1F ) formed in the innerlayer panels can be used with register pins to align the panels during the lamination process. According to the present invention, the register holes may be formed without the necessity of etching to expose fiducials. The innerlayer panels can be bonded together using, for example, dielectric prepregs. The printed wiring board  1000  may be laminated in multiple stages. For example, subassemblies of innerlayer panels may be processed and laminated, and one or more subassemblies can subsequently be laminated together in order to form the finished printed wiring board  1000 . 
     The connection circuitry  1021 ,  1022  can be formed, for example, after all of the innerlayer panels have been laminated together. Alternatively, connection circuitry can be formed in subassemblies of innerlayer panels or in individual panels prior to incorporating all of the innerlayer panels  1100 ,  1200 ,  1300  . . . into the completed printed wiring board  1000 . 
     The connection circuitry between innerlayers can include, for example, one or more conductive vias, extending through all or a part of the printed wiring board  1000 . In  FIG. 2 , the connection circuitry  1021 ,  1022  extend through the entire printed wiring board  1000 , and have the form of through-hole conductive vias. The connection circuitry  1021 ,  1022  can be formed, for example, by laser or mechanically drilling holes through the laminated innerlayer panels. The holes are then plated with a conductive material. The resulting conductive vias  1021 ,  1022 , which extend through the entire printed wiring board  1000 , are typically referred to as “plated through-holes,” and are usually formed after all of the innerlayer panels have been laminated together. 
     Connection circuitry may also extend through subassemblies of innerlayer panels or through individual panels. Conductive vias extending through only a part of the printed wiring board  1000  are commonly referred to as “buried vias.” Buried vias are typically drilled and plated through a subassembly of innerlayer panels before the subassembly of innerlayer panels is incorporated into a printed wiring board by lamination. A small diameter conductive via formed in an individual innerlayer panel is commonly referred to as a “microvia,” and may be used, for example, to terminate a capacitor within an innerlayer panel. 
     After all interconnections have been formed and all subassemblies of innerlayer panels or individual innerlayer panels have been laminated together and the outer layers formed, the printed wiring board  1000  is complete. In  FIG. 2 , the printed wiring board  1000  is illustrated as comprising the innerlayer panels  1100 ,  1200 ,  1300  . . . in a stacked configuration and laminated and connected by the connection circuitry  1021 ,  1022 . Any number of innerlayer panels, however, may be included in a printed wiring board according to the present invention. In addition, only a small portion of the printed wiring board  1000  is illustrated in  FIG. 2 , and many more features and connection circuitry may be present in the printed wiring board  1000 . 
     Each of the innerlayer panels can have a different design, including differing arrangements of circuit elements. The term “innerlayer panel” does not imply that the panels must be sandwiched in the interior of the printed wiring board  1000 , and the innerlayer panels can also be located at the ends of the printed wiring board  1000 . 
     The fiducials  20  illustrated in the above embodiments may be of any thickness, density and shape that allows for reliable identification of the fiducials  20  through the innerlayer panel  100 . In general, the fiducials  20  should be of relatively high density. Use of high-density materials in the fiducials  20  allows for identification of the location of the fiducials by X-rays through lower density layers, such as the foils used to form features in the panel  100 . 
     In one embodiment, the fiducials  20  are formed from a high-density paste. In the electronic materials industry, the term “paste” generally refers to a thick-film composition. Generally, thick-film pastes comprise finely divided particles of ceramic, glass, metal or other solids dispersed in polymers dissolved in an organic vehicle containing a mixture of plasticizer, dispersing agent and organic solvent. The glasses in the pastes can be, for example, Ca—Al borosilicates, Pb—Ba borosilicates, Pb-borosilicates, Mg—Al silicates, rare earth borates, and other similar glass compositions. The vehicles generally contain very small amounts of resin, such as high molecular weight ethyl cellulose, where only small amounts are necessary to generate a viscosity suitable for screen-printing. Solids are mixed with the vehicle, then dispersed on a three-roll mill to form a paste-like composition suitable for screen-printing. Any essentially inert liquid may be used as the vehicle. For example, various organic liquids, with or without thickening and/or stabilizing agents and/or other common additives, may be used as the vehicle. 
     One embodiment of a high-density paste includes tungsten powder and a small amount of glass dispersed in the organic vehicle. The organic vehicle has good burnout in a nitrogen atmosphere. This paste is particularly suitable for use with copper foils. The tungsten-containing high-density paste can be fabricated by, for example, dispersing tungsten powder in a screen-printing medium. Glass powder is an additive that promotes cohesion of the tungsten powder to itself and adhesion to the copper foil after firing at high temperatures. 
     The fiducials  20  may be of similar or slightly greater thickness to the features  12  formed over the foil  10  (see  FIG. 1B ). This arrangement is desirable because a screen-printing process can be used. Dried fiducial thicknesses favorable to detection by X-rays are generally 15 microns or greater. 
     Pastes comprising high-density metals are particularly suitable for forming fiducials. High-density metals are generally defined as having a density of 16 g/cc or higher. Tungsten, iridium, platinum, rhenium, tantalum, osmium, uranium or gold are examples of high density metals. 
     Tungsten is a preferred metal for forming fiducials because it does not alloy with copper. When a fiducial containing tungsten is formed over a copper substrate, there is an abrupt interface between the copper and the tungsten, which allows for better detection of the fiducial by X-rays. Tungsten is also relatively cheap and available in fine powder form. 
     The fine powder form of tungsten can be incorporated into a vehicle to form a printable paste. A tungsten-containing paste, for example, may be formed by mixing tungsten powder with glass powder. Upon firing during manufacture of an innerlayer panel, the glass in the paste forms a bond between the tungsten and the copper substrate. A suitable firing temperature may be in the range of about 900° C. 
     A tungsten-containing paste may also be formulated as a “polymer thick-film” paste composition. Such a polymer thick-film paste composition may contain a high quantity of tungsten, such as greater than 80% by weight dispersed in an epoxy vehicle system. The polymer thick-film tungsten paste is preferable when polymer thick-film elements are being formed on copper foil. The polymer thick-film tungsten paste may be cured at between 150-200° C. for approximately ½-1 hour, for example, to cure and to harden the deposited paste. A polymer thick-film tungsten-containing paste is resistant to the black oxide process. 
     The following examples describe embodiments of the invention. 
     EXAMPLE 1 
     A paste of the following composition was formed:
         vehicle 8.85%   TEXANOL® solvent 5.23%   glass powder 27.50%   tungsten powder 58.42%       

     The vehicle was composed of 11% ethyl cellulose N200 dissolved in 89% TEXANOL® available from Eastman Chemical Co. The glass powder was composed of 5.4% SiO 2 , 4.1% Al 2 O 3 , 78.1% PbO, and 12.4% B 2 O 3  and was ground to a particle size of approximately 1 micron. The glass powder softening point was approximately 472° C. The tungsten powder was 1-5 microns in diameter. The inorganic solid content (glass and tungsten powder) was 85.92 weight %. 
     The tungsten-containing paste was used to print ring fiducials of approximately 1 cm outer diameter and ½ cm inner diameter. The fiducials were printed onto 1 oz (36 micron) copper foils having passive ceramic components printed thereon. This arrangement is generally illustrated by  FIG. 1A . The ring fiducials were printed at specific locations with respect to the passive ceramic component positions. The fiducials were printed prior to printing the passive ceramic components, on the same side of the copper foil as the passive ceramic components. 
     The dried printed thickness of the tungsten-containing paste was approximately 21 microns. The passive ceramic features and the tungsten-containing fiducials on copper foil were fired in nitrogen at 900° C. for 10 minutes at peak. The fired tungsten-containing paste had good adherence to the copper foil. Epoxy protective encapsulants were applied to the passive ceramic components and to the printed fiducials. The component-side face of the foil was laminated to dielectric prepreg and to another copper foil, as shown in  FIG. 1C . 
     The fiducials were clearly identifiable by X-ray. Register holes for use with register pins were drilled at desired locations after identifying the fiducial locations. After etching the foils, the position of the terminations with respect to the components was found to be good. 
     EXAMPLE 2 
     A paste of the following composition was formed:
         vehicle 16.65%   TEXANOL® solvent 4.37%   glass powder 25.26%   tungsten powder 53.72%       

     The vehicle was composed of 11% ethyl cellulose N200 dissolved in 89% TEXANOL®. The glass powder was composed of 5.4% SiO 2 , 4.1% Al 2 O 3 , 78.1% PbO, and 12.4% B 2 O 3  and was ground to a particle size of approximately 1 micron. The glass powder softening point was approximately 472° C. The tungsten-containing powder was 1-5 microns in diameter. The inorganic content of the paste was 78.98 weight %. 
     The tungsten-containing paste was used to print ring fiducials of approximately 1 cm outer diameter and ½ cm inner diameter. The fiducials were printed onto 1 oz (36 micron) copper foils having passive ceramic components printed thereon. This arrangement is generally illustrated by  FIG. 1A . The ring fiducials were printed at specific locations with respect to the passive ceramic component positions. The fiducials were printed prior to printing the passive ceramic components, on the same side of the copper foil as the passive ceramic components. 
     The dried printed thickness of the tungsten-containing paste was approximately 15 microns. The passive ceramic features and the tungsten-containing fiducials on copper foil were fired in nitrogen at 900° C. for 10 minutes at peak. The fired tungsten-containing paste had good adherence to the copper foil. Epoxy protective encapsulants were applied to the passive ceramic components and to the printed fiducials. The component-side face of the foil was laminated to dielectric prepreg and to another copper foil, as shown in  FIG. 1C . 
     In this case, the tungsten-containing fiducials were identifiable by X-ray. There was, however, some reduction in accuracy in locating the fiducial edges, which increased the difficulty in finding the appropriate position to drill the register holes. 
     EXAMPLE 3 
     A paste of the following composition was formed:
         vehicle 29.51%   TEXANOL® solvent 4.8%   glass powder 21.01%   tungsten powder 44.67%       

     The vehicle was composed of 11% ethyl cellulose N200 dissolved in 89% TEXANOL. The glass powder was composed of 5.4% SiO 2 , 4.1% Al 2 O 3 , 78.1% PbO, and 12.4% B 2 O 3  and was ground to a particle size of approximately 1 micron. The glass powder softening point was approximately 472° C. The tungsten powder was 1-5 microns in diameter. The inorganic content of the tungsten-containing paste was 65.68 weight %. 
     The tungsten-containing paste was used to print ring fiducials of approximately 1 cm outer diameter and V 2  cm inner diameter. The fiducials were printed onto 1 oz (36 micron) copper foils having passive ceramic components printed thereon. This arrangement is generally illustrated by  FIG. 1A . The ring fiducials were printed at specific locations with respect to the passive ceramic component positions. The fiducials were printed prior to printing the passive ceramic components, on the same side of the copper foil as the passive ceramic components. 
     The dried printed thickness of the tungsten-containing paste was approximately 10-12 microns. The passive ceramic features and the tungsten-containing fiducials on copper foil were fired in nitrogen at 90° C. for 10 minutes at peak. The fired tungsten-containing paste had good adherence to the copper foil. Epoxy protective encapsulants were applied to the passive ceramic components and to the printed fiducials. The component-side face of the foil was laminated to dielectric prepreg and another copper foil, as shown in  FIG. 1C . 
     In this case, the fiducials were not identifiable by X-ray and register holes could not be drilled. 
     EXAMPLE 4 
     A paste of the following composition was formed:
         vehicle 8.85%   TEXANOL® solvent 5.23%   glass powder 20.92%   tungsten powder 65.00%       

     The vehicle was composed of 11% ethyl cellulose N200 dissolved in 89% TEXANOL. The glass powder was composed of 5.4% SiO 2 , 4.1% Al 2 O 3 , 78.1% PbO, and 12.4% B 2 O 3  and was ground to a particle size of approximately 1 micron. The glass powder softening point was approximately 472° C. The tungsten powder was 1-5 microns in diameter. The inorganic solid content was 85.92 weight %. 
     The tungsten-containing paste was used to print ring fiducials of approximately 1 cm outer diameter and ½ cm inner diameter. The fiducials were printed onto 1 oz (36 micron) copper foils having passive ceramic components printed thereon. This arrangement is generally illustrated by  FIG. 1A . The ring fiducials were printed at specific locations with respect to the passive ceramic component positions. The fiducials were printed prior to printing the passive ceramic components, on the same side of the copper foil as the passive ceramic components. 
     The dried printed thickness of the tungsten-containing paste was approximately 20-22 microns. The passive ceramic features and the tungsten-containing fiducials on copper foil were fired in nitrogen at 900° C. for 10 minutes at peak. The fired tungsten-containing paste had poor adherence to the copper foil. The component-side face of the foil was laminated to dielectric prepreg and to another copper foil, as shown in  FIG. 1C . 
     In samples where protective organic encapsulant was not applied to the tungsten paste, the tungsten-containing fiducials were etched away during the black oxide process. 
     In the case where an organic protective encapsulant was applied to the X-ray paste, the tungsten-containing fiducials survived the black oxide treatment and were clearly identifiable by X-ray after the passive ceramic components were laminated. X-ray register holes could therefore be drilled after lamination. The higher tungsten-to-glass ratio fiducials were identifiable by X-ray. 
     In the above embodiments, the dielectric prepreg and laminate materials can be any type of dielectric material such as, for example, standard epoxy, high Tg epoxy, polyimide, polytetrafluoroethylene, cyanate ester resins, filled resin systems, BT epoxy, and other resins and laminates that provide insulation between circuit layers. 
     The features  12  may be capacitors, resistors or any other circuit element or components. There may also be features such as preformed via bumps that require alignment with circuitry. 
     The embodiments described in this specification have many applications. For example, one or more of the capacitor embodiments can be used within organic printed circuit boards, IC packages, applications of such structures in decoupling applications, devices such as IC modules and devices or handheld device motherboards; and other applications. 
     Each of the innerlayer panels in the printed wiring board  1000  can have a different design, including differing arrangements of circuit elements. 
     The foregoing description illustrates and describes the preferred embodiments of the present invention. It is to be understood that the invention is capable of use in various other combinations, modifications, and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein, commensurate with the above teachings, and/or the skill or knowledge of the relevant art. 
     The embodiments described hereinabove are further intended to explain best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with the various modifications required by the particular applications or uses of the invention. Accordingly, the detailed description is not intended to limit the invention to the form disclosed herein. Also, it is intended that the appended claims be construed to include alternative embodiments.