ALUMINA MATERIALS FOR LOW TEMPERATURE CO-SINTERING WITH REFRACTORY METALLIZATION II

Abstract: High quality ceramics, especially useful as substrates for integrated circuit packages, are produced from particles having a size distribution such that the standard deviation is approximately 20 % - 100 % of the mean particle size. The mean particle sizes range from about 0.3 to about 1.0 microns, and after processing and sintering, the mean grain size ranges from about 0.4 to about 1.4 microns and the narrow distribution of grain sizes also exhibits a standard deviation of about 20 % to about 100 % of the mean grain size. These distributions are broader than the essentialy monosized distributions currently employed in the art for the highest quality substrates suitable for thin film metallization but provide substrates suitable for co-sintering with internal metallization. Also, these distributions are narrower than those used for thick film applications, yet the present ceramics exhibit improved thermal conductivity, a low shrinkage variability, and a smooth surface finish of less than 3.0 microinches, less than 2.0 microinches with a standard deviation of up to about 100 % of the mean, and down to about 1.0 microinch with a standard deviation of up to about 50 % of the mean. These ceramics are suitable for thin film metallization as well as for co-sintering with refractory metallization, such as thick film technology.

Description: ALUMINA MATERIALS FOR LOW TEMPERATURE CO-SINTERING WITH REFRACTORY METALLIZATION II This application is a continuation-in-part of applicants' co-pending application Serial No. 935,513, filed Nov. 26, 1986. Description This invention relates to ceramic packages for integrated circuits, and in particular, to ceramics which have a narrow size distribution of grains, or of particles in green ceramics, improved thermal conductivity, low shrinkage variability, a smooth surface, and can be co-sintered with metal pastes at low temperatures. Background Art Ceramics have found widespread use in electronics as a substrate for integrated circuit packages. Such packages are generally made by applying metallized circuit patterns to the ceramic substrate, and ceramic and metallization are co-sintered to create a monolith of substrate and circuitry. Multi-layer circuit packages are constructed by first creating a substrate by combining ceramic particles and organic binders into an unfired, or "green," tape. Inter-layer conductive paths, known as "vias," are then created in the tape layers, for forming electrical interconnections between the circuits on different layers after they are stacked and processed. Thereafter, metallized circuit patterns are applied. The tape layers typically have thicknesses ranging from 5 to 25 mils. Holes and notches are formed in the layers as required. Multiple layers of printed tapes are stacked and then laminated under pressure, and ceramic and metallized patterns are co-sintered to form a monolithic structure with three-dimensional circuitry. Typically, substrates are formed from a combination of approximately 90-94% broad size distribution alumina and 6-10% silicon-based glass; a tungsten- or molybdenum/manganese-based paste is used to form the metallized conductive patterns and vias. The glass is added to the alumina to promote bonding of the metallization to the alumina and to provide sintering of the alumina at a lower temperature than for 98+% alumina. Upon co-firing of the alumina and paste, the glass component migrates from the alumina layer to the paste layer, providing interfacial adhesion between the paste component and the substrate and also for promoting bonding. Substrates have typically been formed from particles ■ having a broad size distribution. The prior art relating to thick film technology used for the above-described multilayer packages describes the production of a densely-packed body from a mixture of particles having a broad size distribution. It was thought that a mixture of large and small particles was necessary so that small particles would fill the interstices between large particles and hence provide maximum packing of particles. Circuit packages produced from such prior art formulations typically display a dielectric constant of approximately 9-9.5, thermal conductivity of approximately 0.45 cal-cm/cm 2 -sec- β C at 20"C (compared with .085 cal-cm/cm 2 -sec- β C for 99.5% alumina), a shrinkage variability of 1.0% (while 0.5% is considered optimal at present) , and a surface finish of greater than 25 microinches. While these substrate properties may have been acceptable for conventional semiconductor packages, they are inadequate for high-performance large scale integration applications and other specialized applications. They are especially inadequate for the further application of thin film metallization due to their poor surface finish, as discussed below. The use of a broad size distribution of particles generally results in non-uniform particle packing within the ceramic tape, which in turn leads to shrinkage variability during the co-firing (sintering) operation. Shrinkage variability exacerbates the problem of meeting critical dimensional tolerances when co-sintering with conductor films. Reducing shrinkage variability is critical for process control and product quality in a broad range of applications, and is especially important as feature size decreases. This is because variability in shrinkage prevents precise location of circuit paths, vias, and other interconnections, and often results in the need to reject the ceramic circuit packages because of electrical discontinuities between internal interconnections, and, in the case of thin-film applications, results in additional discontinuities between co-fired metallization and subsequently applied thin-film metallization. A reduction in shrinkage variability from the prior art 1% level would increase product yield, and benefit both the substrate manufacturer and substrate consumer, who may, for example, require precise positioning of devices and interconnections for reliable post-fire circuit personalization by thin-film metallization. Thick film technology generally relates to ceramic substrates having relatively thick metallization traces formed from the inks described above. In contrast, thin film technology refers to conductive paths or traces which are dramatically smaller in size, particularly with respect to the vertical measurement above the substrate surface. In this regard, surface finish also becomes increasingly important as feature size decreases. In microelectronic circuits produced by thin-film metallization techniques, the conductor thickness can be as small as a few microns (1 micron is approximately 40 microinches) . Accordingly, if the substrate has a 25 microinch surface finish typical of the prior art 94:6 alumina:glass substrates used for thick film applications, the conductor path will have substantial differences in thickness along its length, or may even be discontinuous, with a corresponding degradation of function. Accordingly, roughness of surface finish prevents post-firing circuit personalization by thin-film metallization. The use of a broad size distribution of particles results in a relatively rough surface finish which requires polishing to yield a surface suitable for thin film deposition. Polishing techniques can improve the surface finish to some extent, but further improvement through polishing is not possible because the polishing process plucks larger particles off the surface, leaving pockets and voids and thus increasing porosity. In addition, polishing significantly increases the production cost. The alumina-glass substrates suitable for thick film applications are also used for the multilayer packages described previously. However, they are unsuitable for thin film hybrid packages, i.e., a package having thick film metallization and a top-most layer suitable for thin film metallization, because of the poor surface finish of such alumina-glass substrates. Moreover, porosity of the as-fired surface, especially when combined with surface roughness, leads to the problem of retention of plating salts. Aggressive cleaning procedures are required to avoid deposition of plating salts where not desired, and to avoid blistering upon firing. Greater smoothness and a lessening of porosity would allow the use of more active catalysts, which in turn would increase product yield through electroless plating operations. It is important to note that thin film metallization is usually employed on 98+% alumina substrates because of their better surface finish» However, a thin film metallization cannot be co-sintered with a typical green ceramic substrate because the metallization will not shrink as the substrate does during the sintering process. Thus, the metallization buckles and becomes discontinuous, thereby resulting in an unsuitable product. Especially regarding the production of substrates having density and surface finish characteristics suitable for thin film metallization, Stetson et al., in U.S. Pat. No. 3,698,923, attempted to use a fine powder but having a broad size range distribution analogous to that used for thick film substrates. However, the density and surface finish obtained were not ideally suitable for thin films. More recent developments in the art directed to substrates suitable for thin film metallization have tended towards the opposite approach by using an extremely narrow, essentially uniform size distribution of particles for making the substrate. Such approaches are described by Agarwal et al., in U.S. Pat. No. 4,678,762, and by Gattuso and Bowen in "Processing of Narrow Size Distribution Alumina", Advances in Ceramics, vol. 10, 644-655 (1983). The method described in these references includes the use of ceramic particles having a size range of 0.1-0.3 micron to achieve a dense substrate with a surface finish of less than about 40 nm (about 1.57 microinches) and a grain size of less than about 0.4 micron. Moreover, Agarwal et al. notes that if the same size range, 0.2 micron, is used but the actual particle sizes are 0.5-0.7 micron, then coarser surface finishes (e.g., 80 nm, about 3.15 microinches) are obtained. These results are expected in view of the literature, which provides a correlation between grain size and actual surface finish. See Stetson, Mistier, and Gyurk, "A Theoretical Discussion of Surface Finish of Ceramic Substrates," Int. J. Hybrid Microelec. , vol. 37, no. 1, p. 621-624 (1983). This article predicts that a grain size of 0.6 micron should yield a surface finish of no worse than 40 nm, similar to what Agarwal et al. describes. Current art 90-94% alumina substrates for multilayer applications are unsuitable for thin film metallization. Additionally, commercial 98+% alumina substrates for thin film applications have not been successfully co-sintered with internal metallization. Accordingly, there exists a need for a substrate material with low shrinkage variability, an as-fired surface finish suitable for thin film deposition, superior thermal characteristics, and especially suitable for co-sintering with refractory metallization. Disclosure of Invention We have discovered that circuit packages can be produced by using a substrate consisting of at least 98% narrow size distribution alumina particles in conjunction with a metallization paste to which selected compositions of bonding agents glass have been added. This metallization paste is further discussed in our copending application Serial No. 935,264, filed Nov. 26, 1986, which is incorporated by reference herein. Preferred ink composition for vias are described in copending application Serial No. 053,323, filed May 22, 1987, also incorporated by reference herein. Circuit packages produced in accordance with the present invention exhibit superior thermal conductivity, low shrinkage variability, a smoother and more homogeneous surface finish suitable for thin film metallization, and are also suitable for co-sintering with refractory metallization. Employing narrow size range ceramic powder improves shrinkage and surface finish parameters and reduces sintering temperature. Further details and embodiments of the invention are described below. Description of Specific Embodiments A preferred embodiment of the invention utilizes narrow size range alumina powder having a mean particle size in the range of 0.3 to 1.0 micrometer with a standard deviation not greater than approximately 100% of mean. The use of narrow size range alumina particles allows sintering at low temperatures, typically 1500-1550 β C, compared with 1600-1700°C for wide size range alumina particles typical of commercial powders. (Because fired ceramics exhibit some grain growth in comparison to starting particle size, a green body derived from the narrow size range powder described above would be expected to exhibit grains having a respective mean size in the range of 0.4 to 1.4 micrometers after firing.) Moreover, this lower sintering temperature for narrow size range alumina is achieved without the necessity of adding glass and other sintering aids to the alumina substrate, with its concomitant decrease in thermal conductivity. We have found that throughout a range of particle sizes, the respective thermal conductivities of 92% alumina and 99.5% alumina are .045 and 0.085 cal-cm/cm 2 -sec- β C at 20°, respectively. Alumina substrates produced in accordance with the present invention therefore exhibit nearly double the thermal conductivity of prior art cofired alumina substrates. Using narrow size range alumina particles permits more uniform green densities, and in a 98+% ratio, produces a fired ceramic having an excellent surface finish suitable for thin film deposition. In contrast, typical prior art substrates for cofiring produced from wide size range 90-94% alumina and 6-10% glass require polishing, which increases cost and creates voids. The narrow size range particles of the present invention are distinct from those of the art described above. As noted previously, the art has resorted to a broad particle size range (e.g., stetson et al.) and to an essentially uniform particle size range (e.g., Agarwal et al.), with the common goal of at least providing an improved surface finish. In contrast to both of these art approaches, we have discovered that particles of a size range narrower than first proposed in the art yet broader than what is conventionally considered to be the state of the art for thin film technology provides dense substrates having surface finishes at least as good as those presently achieved. As used herein, a "narrow" size distribution includes particles having a mean size in the range of approximately 0.3-1.0 microns and exhibiting a standard deviation of no greater than approximately 100% of the mean (i.e., the mean particle size) and no less than approximately 20% of the mean, preferably no less than 30% of the mean. Upon sintering, the substrate includes "narrow" size distribution ceramic grains of a mean grain size in the range of approximately 0.4-1.4 microns and also exhibiting a standard deviation of from about 20%, preferably from about 30%, to about 100% of the mean grain size. In the present instance, it is particularly preferred that the standard deviation can range from 50% up to about 100% of the mean. With reference to our copending application Serial No. 935,513 of which this application is a continuation-in-part, we have discovered that an even broader size distribution of particles can achieve the requisite substrate characteristics. The ceramic materials to which the present invention pertains are derived from crystalline powders as opposed to amorphous powders. Further, although the present invention is illustrated hereinafter primarily by the use of alumina, this invention is equally applicable to substrates derived from other ceramic powders, such as, but not limited to, zirconia, silicon carbide, silicon nitride, aluminum nitride, and composites and mixtures thereof. This invention is also applicable to metals which, when in a powdered form, can be sintered or fused together by the application of heat. Such materials include, but are not limited to, aluminum, copper, nickel, and the alloys of each. Generally, a preferred embodiment of the invention involves the production of a green tape of 98+% narrow size distribution alumina particles, from a slip including a homogeneous mixture of ceramic and organic components. The slip is prepared from sequential additions of dispersed alumina powder, solvent, and plasticized binder, which are ball milled for 36-60 hours to a desired viscosity. After de-airing, the slip is delivered to a carrier material where a doctor blade levels it to a constant thickness which will shrink to a calculated thickness after solvent evaporation. A wide variety of slip constituents will produce an acceptable tape. Typical solvent systems consist of combinations of: cyclohexanone, methylethyl or isobutyl ketone, methanol, ethanol, n-propanol, isopropanol, toluene, and xylene. Preferred binders are polyvinyl butyral resins (such as those identified by the trade designations B-76, B-79, B-90, and B-98 available from Monsanto, St. Louis, MO, as "Butvar" resins) and methacrylate polymers and copolymers, preferably alpha-substituted methacrylate esters (such as those designated Elvacite -2014, -2016, -2028, and -2046, available from E.I. DuPont de Nemours Corp., Wilmington, DE, or those designated under the Acryloid trademark, available from Rohm and Haas Co., Philadelphia, PA). Effective plasticizers include dibutylphthalate, dioctylphthalate, and mixed phthalates (such as those identified by the trade designations PX-316 and PX-126, available from USS Chemicals, Pittsburgh, PA) . Other plasticizers may be usefully employed, including adipates such as dioctyl adipate (available from Hexanon Enterprises, Inc., Mountain Lakes, NJ) , castor oil derivatives, or polyalkylene glycols and diesters (such as those under the designation Ucon, available from Union Carbide Corp., New York, NY). These additional plasticizers can be used alone, and are especially prefered in combination with a phthalate-based plasticizer. The present system includes a dispersant, such as fish oil, triethanolamine, an organic phosphate ester (such as that designated Gafac RE-610, available from GAF Corp., Wayne, NJ) , or general purpose surface active agent (such as those designated Span, e.g. Span 85, available from ICI Americas, Wilmington, DE) , Emcol CC55 (available from Witco Chem. Co., Perth A boy, NJ) , or organometalliσ coupling agents, particularly those having an alkoxy moiety, or mixtures thereof. Binder additions are in the range of 38 to 44 volume percent with polymer to plasticizer ratios ranging fom 0.5:1 to 4:1 depending on the laminating, punching, and shrinkage characteristics desired. Typically, a slip is prepared in a two stage milling process. In the first stage, the ceramic powder, solvent(s) , and dispersant(s) are mixed. In the second stage, the polymer(s) and plasticizer(s) are added. In a further preferred embodiment, multi-layer circuit packages are constructed by combining layers of ceramic tape to which are applied metallized circuit patterns. The tape layers typically have thicknesses ranging from 5 to 30 mils (125-765 micrometers) . Vias are provided through the layers, and notches are formed in the layers as required. Metallization ink is applied, the layers are laminated under pressure, and the multilayer laminate is co-sintered. Typical co-sintering operations involve heating the laminate to 1200 β C and maintaining this temperature for 1-3 hours, heating the laminate to the peak firing temperature (typically 1500-1550 β C) , and maintaining this temperature for 1/2-2 hours in an atmosphere of dissociated ammonia and nitrogen (50% H 2 and 50% N 2 ) and water vapor at a dew point ranging from 15-45°C. Colorants, such as MnO, M0O3, Cr 2 0 3 , or Ti0 2 , or a combination thereof, may be added in amounts up to approximately 2% by weight to opacify the fired ceramic, while preserving the advantageous characteristics of the invention, although lesser amounts (for example, 0.25% Mo0 3 ) may suffice. The following examples are illustrative of the invention: In each of the examples below, the slip is milled in two 24 hour stages. In the first stage the powder, solvents, and a small amount (about 8-15% by weight of the total) of polymer are milled to ensure good dispersion of the powder in the liquid phase. The second stage of milling is done with the addition of the rest of the polymer and plasticizer. Example 1 Stage I Milling: Component Weight Percent Ceramic powder alumina (average 58 0.5 micrometers, standard deviation 0.15) . Solvent methyl ethyl ketone 16 Solvent toluene 16 Polymer Polyvinyl Butyral 0.7-1.1 B-79 Stage II Milling: Polymer Polyvinyl Butyral 5.9-6.3 B-79 Plasticizer Phthalate PX-316 Example 2 Stage I Milling: Component Weight Percent Ceramic powder alumina (average 56 0.5 micrometers, standard deviation 0.15) Solvent methyl ethyl ketone 17 Solvent toluene 17 Polymer Polyvinyl Butyral 0.8-1.2 B-79 Stage II Milling: Polymer Polyvinyl Butyral 6.8-7.2 B-79 - Exa ple 3 Stage I Milling: Component Weight Percent Ceramic powder alumina (average 55 0.5 micrometers, standard deviation 0.15) Solvent ethanol 13 Solvent xylene 20 Polymer Polyvinyl Butyral 0.6-0.9 B-90 Stage II Milling: Binder Polyvinyl Butyral 5.1-5.4 B-90 Plasticizer dibutylphthalate 6 Example 4 Material Composition Weight Percent Stage I Milling: Ceramic powder Alumina 57.5 Solvent Toluene 15.7 Solvent Methyl Ethyl Ketone 15.7 Polymer Polyvinyl Butyral B-79 0.6 Dispersant Triethanolamine 0.3 Stage II Milling: Polymer Polyvinyl Butyral B-79 6.9 Plasticizer Dibutyl Phthalate 3.3 These tapes typically yield a green-to-fired shrinkage variation of less than +0.25% at firing temperatures in range of 1510-1540°C and density of >98% of theoretical. " " ' Example 5 Alumina particles were centrifugally classified (as described in copending applications Serial Nos. 028,757 and 028,891, both filed March 23, 1987, the disclosures of both of which are incorporated by reference herein) to provide theoretical particle sizes of <0.7 micron. The actual particle size measurement and distribution date were as follows: Group 1 2 3 4 Mean Particle Size (micron) 0.44 0.52 0.51 0.46 Standard Deviation 0.18 0.25 0.23 0.19 as % of mean 41 48 45 41 These particles were processed as described herein above, including the two-stage milling and subsequent sintering. The resulting substrates exhibited an average grain size of 0.5 micron and a surface finish of 1.00-1.75 microinches. Example 6 Alumina particles were centrifugally classified to provide particles having a theoretical size range of 0.5-0.8 micron; the measurement date showed the actual mean particle size range to be 0.5-0.7 micron and the standard deviation to be 30-35% of the mean. After further processing and sintering, the substrates showed an average grain size of less than one micron and a surface finish of 1.75-2.00 microinches. Example 7 Alumina particles were classified to provide a theoretical size range of 0.3-0.5 micron; the actual measured mean particle size range was 0.45-0.55 micron and the standard deviation was about 30% (25-35%) of the mean. These tapes were fired at about 1475"C, and the sintered substrate had a- density of 97+% theoretical. The resulting surface finish of the substrates was 1.0-1.5 microinches. Example 8 Alumina particles were classified to provide an actual particle size range of about 0.3 - 1.2 microns. Random samples of these classified particles were examined for their size distribution and the standard deviation thereof with the following results: Sample 1 Mean Particle Size 0.53 0.54 0. 47 Standard Deviation 0. 40 0. 51 0 . 44 as % of mean 75.5 94 .4 93 . 6 Random samples of these classified particles were processed in accordance with the two stage milling described above and tape cast and sintered. The air-side surface finish (which is typically worse than the tape-side finish when a high quality carrier surface is used) of various sintered tapes were as follows: Tape _1 2 3 4 5 Surface Finish 2.07 2.05 1.83 2.16 2.50 (microinches) The foregoing descriptions and examples are meant to be illustrative and in no manner limiting. Various modifications of the invention as described may be determinable by the skilled artisan, and such are meant to be within the scope and spirit of the invention as defined by the following claims. ~

Claims: What is claimed is: 1. An as-fired ceramic substrate having a density of at least 97% theoretical, consisting essentially of narrow size distribution ceramic grains having a mean grain size in the range of about 0.4-1.4 microns with a standard deviation in the range of about 20%-100% of the mean grain size, the substrate derived from crystalline powders. 2. A substrate according to claim 1, wherein the ceramic- is alumina, zirconia, silicon nitride, silicon carbide, aluminum nitride, or composites or mixtures thereof. 3. A substrate according to claim 1, wherein the surface finish is not more than about 3.0 microinches. 4. A substrate according to claim 1, wherein the surface finish is not more than about 2.0 microinches. 5. A substrate as defined by claim 1, wherein the standard deviation is in the range of approximately 30%-100% of the mean. 6. A substrate as defined by claim 1, wherein the standard deviation is in the range of approximately 20%-50% of the mean. 7. A substrate as defined by claim 1, wherein the standard deviation is in the range of approximately 30%-50% of the mean. 8. A substrate as defined by claim 1, wherein the standard deviation is in the range of approximately 50%-100% of the mean. 9. An as-fired multi-layer ceramic-based circuit package comprising: laminated layers of ceramic substrate, each layer having a density of at least 97% theoretical and consisting essentially of narrow size distribution ceramic grains having a mean grain size in the range of about 0.4-1.4 microns with a standard deviation in the range of about 20%-100% of the mean grain size, the substrate derived from crystalline powders; and at least one conductive layer interspersed between the layers of ceramic substrate. 10. A circuit package according to claim 9, wherein the ceramic is alumina, zirconia, silicon nitride, silicon carbide, aluminum nitride, or composites or mixtures thereof. 11. A substrate according to claim 9, wherein the surface finish is not more than about 3.0 microinches. 12. A substrate according to claim 9, wherein the surface finish is not more than about 2.0 microinches. 13. A slip consisting essentially of crystalline ceramic particles having a mean particle size in the range of about 0.3-1.0 microns with a standard deviation in the range of about 20% to 100% of the mean particle size, a solvent system, a binder resin, a dispersant, and a plasticizer. 14. A slip according to claim 13, wherein the ceramic is alumina, zirconia, silicon nitride, silicon carbide, aluminum nitride, or composites or mixtures thereof. 15. A slip according to claim 13, wherein the binder resin is polyvinyl butyral or a methacrylate-based polymer. 16. A slip according to claim 13, wherein the plasticizer is a dialkylphthalate, an adipate, a castor oil derivative, a polyethylene glycol, a glycol diester, or mixtures thereof. 17. A slip according to claim 13, wherein the solvent system is a mixture of components selected from the group consisting of cyclohexanone, methylethyl ketone, methyl-isobutyl ketone, methanol, ethanol, n-propanol iso-propanol, toluene, and xylene. 18. A slip according to claim 13, wherein the dispersant is fish oil, triethanolamine, an organic phosphate ester, an organometalliσ coupling agent, or mixtures thereof. 19. A slip according to claim 13, wherein the standard deviation is in the range of approximately 30%-100% of the mean. 20. A slip according to claim 13, wherein the standard deviation is in the range of approximately 20%-50% of the mean. 21. A slip according to claim 13, wherein the standard deviation is in the range of approximately 30%-50% of the mean. 22. A slip according to claim 13, wherein the standard deviation is in the range of approximately 50%-100% of the mean. 23. A process for producing a ceramic substrate, comprising: a) providing a slip consisting essentially of crystalline ceramic particles having a mean particle size in the range of about 0.3-1.0 microns with a standard deviation in the range of about 50% to 100% of the mean particle size, a solvent system, a dispersant, a binder resin, and a plasticizer; b) forming a tape from the slip; c) drying the tape by evaporating the solvent syste ; and d) sintering the dried tape 24. A slip according to claim 23, wherein the ceramic is alumina, zirconia, silicon nitride, silicon carbide, aluminum nitride, or composites or mixtures thereof. 25. A slip according to claim 23, wherein the binder resin is polyvinyl butyral or a methacrylate-based polymer. 26. A slip according to claim 23, wherein the plasticizer is a dialkylphthalate, an adipate, a castor oil derivative, a polyalkylene glycol, a glycol diester, or mixtures thereof. 27. A process according to claim 23, wherein the solvent system is a mixture of components selected from the group consisting of cyclohexanone, methylethyl ketone, methyl-isobutyl ketone, methanol, ethanol, n-propanol, isopropanol, toluene, and xylene. 28. A process accoding to claim 23, wherein the dispersant is fish oil, triethanolamine, an organic phosphate ester, an organometallic coupling agent, or mixtures thereof.

Inventors: BARRINGER ERIC A, LIND ROGER S, PORMEY ELLEN S, SWAIN CHARLES E, BARRINGER, ERIC, A., LIND, ROGER, S., PORMEY, ELLEN, S., SWAIN, CHARLES, E.
Applicants: CERAMICS PROCESS SYSTEMS, CERAMICS PROCESS SYSTEMS CORPORATION
Application year: 1987
Main classification: C04B35
IPC codes: C04B35, H01L23, H05K1