GB2243803A

GB2243803A - Lamination of integrated circuit packages

Info

Publication number: GB2243803A
Application number: GB9103242A
Authority: GB
Inventors: William O Park
Original assignee: Cabot Ceramics Inc
Current assignee: Cabot Ceramics Inc
Priority date: 1990-02-20
Filing date: 1991-02-15
Publication date: 1991-11-13
Also published as: DE4105275A1; JPH04214640A; FR2658661A1; CA2036169A1; GB9103242D0; KR920000129A

Abstract

Laminated integrated circuit packages are prepared using an apparatus and process that consolidates the package without the use of fluids and nonconforming dies. A plurality of laminates (12) from which the package is formed are stacked on a base (32). A pressure transfer membrane (60) having two layers, a silicone rubber release layer (62) adjacent the stack and a urethane rubber separating layer (64). is placed over the stack of laminates. A solid pressurizing medium (54), preferably retained by a latex diaphragm (58) in a cavity (48) in a pressurizing tool (42), is pressed against the pressure transfer membrane and the underlying stack to consolidate the stack of laminates. Preferably, heat is applied simultaneously with the pressing to aid in consolidation, and the region between the pressure transfer membrane and the stack of laminates is evacuated to remove air bubbles that might locally prevent lamination. <IMAGE>

Description

i...4 -:3 a. -:3 r- - LAMINATION OF INTEGRATED CIRCUIT PACKAGES

BACKGROUND OF THE INVENTION

This invention relates to the preparation of laminated integrated circuit packages, and, more particularly, to the formation of such packages from a stack of sheets.

Integrated circuits are electronic devices that are extremely miniaturized, so that hundreds or even thousands of Individual circuits and active elements are formed on a chip that may be only 112 inch on a side. The reduction in size of such circuits reduces their weight and volume, and also increases their operating speeds because the distances that electrons must travel are reduced.

The widespread adoption of integrated circuitry has revolutionized many areas of electronics.

The integrated circuits themselves are extremely small and fragile. They must therefore be packaged and protected in a manner that permits external electrical connections to be made, and permits the Integrated circuits to be handled in a normal manner during the assembly and repair of electronic devices packaged integrated One common integrated circuits that may utilize one or many such circuits.

approach to the packaging of is to mount the circuits on a ceramic substrate, which is commonly termed a "Package" in the industry. In the earliest packages, there was a single layerof ceramic. More recently, as the integrated circuits have become more complex, the packages have also become more complex. Now, some packages are formed of two or more layers of ceramic laminate, with various layers having openings therethrough to permit interlaminate 1 J connections and a variety of complex functions of the package itself that augment the function of the integrated circuit and permit the various required external and internal interconnections and circuit paths.

In one procedure for the preparation of multilayer ceramic packages, sheets of unfired ceramic material in a plastic binder (termed "green" ceramic) having a relatively low density such as 50-60 percent of the theoretical fully compacted density are processed to have metallic traces and contacts thereon, cut and trimmed to have the necessary shapes, including the openings therethrough, and then stacked on top of each other in the proper sequence and alignment. A heated tool having the proper shape of the upper surface of the final ceramic package is pressed downwardly against the surface of the stack, causing the laminates to consolidate to about' 60-65 percent of theoretical density and also causing the laminates to stick together. The compacted package is then fired at elevated temperature to increase the package density to about 96 percent of the theoretical density, which is sufficiently strong to carry the integrated circuit. The integrated circuit is fastened to the surface of the package, electrical connections are made, and a protective cover is sealed into place, thereby completing the fabrication of the packaged integrated circuit.

While operable, this procedure is subject to process variations that can affect the quality of the final packaged product. It is difficult to control the distribution of pressure in the metallic pressing tool, with the result that different portions of the package are compressed by different amounts. The more highly compressed portions shrink less than the less compressed portions, with the 1 There Improve the ability of manufacturing disclosed in result that the package tends to warp. Also, there may be small item-to- item variations in the thicknesses of the laminates, and the rigid tool is not well suited to adapt to such variations.

have been variations proposed to uniformity of the packages and the the processing to tolerate normal variability. In one approach, US Patent 4,636,275, the rigid tool is replaced by a pressurized fluid. The fluid is enclosed in a rubber or other elastomer bladder that contacts the upper surface of the stack of laminates.

deformed As the fluid is pressurized, the bladder is against the upper surface of the stack to compress it.

The approach of the '275 patent solves some of the problems inherent with the use of rigid tooling, but suffers from problems of its own. The presence of a fluid requires seals and precautions to prevent leakage that would damage the laminates. If the bladder is too thin, pinholes appearing during repeated flexing in use will allow the fluid to leak. The leakage of fluids is a particularly insidious problem, because very small pinhole leaks that cannot be readily detected may contaminate many packages with microgram quantities of the pressurization fluid before the leak is detected. The manufacturer is then faced with the problem of Identifying the contaminated pieces or throwing away enough of the pieces to be sure that no contaminated pieces remain in the production lot. If the bladder is made thick to minimize the chances of leakage, it may not conform to small openings in the stack or may cause unacceptable rounding of the edges of openings. Experience with rubber bladders used in other contexts suggests that a bladder sufficiently thick to reliably contain the pressurizing fluid t will not reach into small via openings about 0.010-0.050 inch in diameter and will also round the corners of larger openings. Moreover, the bladder may capture pockets of air around the laminate that prevent complete consolidation. Another problem with bladders is that the materials which can contain fluids are often somewhat tacky to the touch and may stick to the unfired laminates. The result is that the package may be pulled apart when the bladder is removed after pressing.

In yet another approach, some manufacturers using either the rigid tooling or fluid approaches have inserted separate tooling pieces into the stack of laminates. It has been found that multiple sets of inserts are required because of the normal manufacturing variability of the laminates, discussed previously. The insertion and positioning of tooling pieces is a slow process that significantly increases the cost of the final 20 package by slowing the throughput of the lamination process.

Thus, at the present time there is a need for an improved approach to the pressing of laminates used in microcircuit packages. The approach should attain the advantages possible with the various previously developed lamination procedures, and not incorporate their shortcomings. The present invention fulfills this need, and further provides related advantages.

SUMMARY OF THE INVENTION

The present invention provides a process and apparatus for laminating microcircuit packages from stacks of laminate sheets that have been previously patterned and cut to shape. The approach provides a quasi-hydrostatic lamination pressure that has been found operable to consolidate stacks of laminates having openings through laminate layers as small as 0.020 Inches, without rounding of the edges. The approach accommodates normal variations in laminate thickness and quality, so that only a single apparatus is required. No fluids Is are used, and there no danger of leakage and contamination of the packages. The approach is operable in a production context to process laminated packages rapidly and at low cost.

In accordance with the Invention, apparatus for fabricating an Integrated circuit package from a plurality of layers of laminates comprises a base upon which the laminates are stacked to form a stack having an upper surface; a solid pressurizing medium disposed in a facing relationship to the stacked laminates, the pressurizing medium being made of a material, that deforms to conform to the upper surface of the stack of laminates under pressure but which returns to substantially its undeformed state in the absence of pressure; and a pressure transfer membrane between the pressurizing medium and the upper surface of the stack of laminates that is sufficiently flexible to conform to the upper surface of the stack of laminates, the pressure transfer membrane having a first layer adjacent the laminates that does not adhere to the laminates and a second layer adjacent the pressurizing medium that prevents contact between the pressurizing medium and the laminates.

The solid pressurizing medium Is preferably a polyurethane rubber block made of SorbothaneTM brand material. Such a material can conform to the upper surface of the stack of laminates." Preferably, the pressurizing medium Is retained by a latex diaphragm in a cavity of a pressurizing tool facing the upper surface of the stack, so that the pressurizing medium is controllably moved into contact with the stack of laminates and then removed.

Some materials that are presently known for use as the pressurizing medium have a degree of stickiness or "tack", so that they would stick to the surface of the stack of laminates in the absence of the pressure transfer membrane. The preferred pressure transfer membrane has two layers, the first layer adjacent the stack formed of a material such as silicone rubber than has no tack and serves as a release agent, and a second layer between the first layer and the pressurizing medium such as a layer of urethane rubber that separates the pressurizing medium from the laminates. Each of the layers is about 0.015 inches thick in the preferred approach, which is sufficiently thin to permit the pressing of small diameter openings such as vias and also does not cause rounding of the edges of large or small openings. Since the pressurizing medium is a solid, there is no possibility of fluid leakage from the apparatus onto the laminates.

It has been found that air bubbles trapped between the pressure transfer membrane and the stack of laminates can prevent bonding locally. The base of the preferred apparatus is therefore intentionally made porous, as by fabricating it from sintered stainless steel. A vacuum is applied to the underside of the base to draw gas from the region between the laminates and between the laminates and the membrane, thereby avoiding such local gas-induced delaminations.

The present approach can, of course, be 3.5 applied to instances wherein the solid pressurizing medium is not tacky. In accordance with this aspect of the invention, apparatus for fabricating an 7 Integrated circuit package from a plurality of layers of laminates comprises a base upon which the laminates are stacked; and a solid pressurizing medium disposed In a facing relationship to the stacked laminates,. the pressurizing medium being made of a material that deforms to conform to the upper surface of the stack of laminates under pressure but which returns to substantially its undeformed state in the absence of pressure.

The pressure transfer membrane of the present invention has wide applicability. In accordance with this aspect of the invention', apparatus for fabricating an integrated circuit package from a plurality of layers of laminates comprises a base upon which the laminates are stacked; a pressurizing medium disposed in a facing relationship to the stacked laminates; and a pressure transfer membrane between the pressurizing medium and the stack of laminate.s that is sufficiently flexible to conform to the upper surface of the stack of laminates, the pressure transfer membrane having a first layer adjacent the laminates that does not adhere to the laminates and a second layer adjacent the pressurizing medium that prevents contact between the pressurizing medium and the laminates.

The present Invention also extends to the process for using the approach of the invention to prepare integrated circuit packages from laminates. In accordance with this aspect of the Invention, a process for pressing integrated circuit packages comprises the steps of providing a stack of laminates to be pressed; providing a pressurizing medium adapted to press against the stack of laminates; placing a layered pressure transfer membrane to overlie at least a portion of the stack of laminates, the pressure transfer membrane having a first layer adjacent the laminates that does not adhere to the laminates and a second layer adjacent the pressurizing medium that prevents contact between the pressurizing medium and the laminates, the pressure transfer membrane being sufficiently flexible to conform to the upper surface of the stack of laminates pressure to transferred under pressure; and applying a the pressurizing medium which is thence to the stack of laminates through the pressure transfer membrane. In the preferred use of the process, the pressurizing medium is a solid material that deforms to conform to the upper surface of the stack of laminates under pressure but which returns to substantially Its undeformed state in the absence of pressure, such as Sorbothane.

The present Invention thus provides an important advance in the fabrication of multilayered packages used to support Integrated circuits. Packages are pressed and consolidated In a quasi-hydrostatic manner that achieves uniform pressing that leads to uniform density distribution, without rounding of corners and closure of small openings. No potentially leaky fluids are used in the pressing operation. The approach is operable in large-scale commercial manufacturing operations.

Other features and advantages of the Invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.

Figure 1 ceramic package; Figure 2 BRIEF DESCRIPTION OF THE DRAWINGS is a side sectional view of a is a side sectional view of a 1 pressing apparatus; and Figure 3 is a detail of Figure 2, showing the arrangement and construction of the pressure transfer membrane.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Figure 1 illustrates a ceramic package 10 of the type that can be pressed using-the approach of the invention. The package 10 is formed from a plurality, in this case three, laminates 12 of unconsolidated ceramic material. The laminates are formed by preparing sheets of ceramic oxides such as aluminum oxide and small amounts of glass-forming oxides, mixed with an organic binding material such as polyvinyl butyral. A typical mixture includes about 90 percent by weight of the ceramic oxide powders and 10 percent by weight of binder, although these relative densitv of amounts may vary. The sheets have a about 2.1 grams per cubic centimeter, as compared with a density of about 4.0 grams per cubic centimeter for fully dense aluminum oxide. Thus, the sheets, termed "green" material, have a density of just over 50 percent of the theoretical full density of the aluminum oxide.

As shown in Figure 1, the laminates 12 are stacked on top of each other to form a stack 14 of laminates. The bottom laminate is a full sheet, to support an integrated circuit 16 thereupon. The other laminates have openings is and 20 therethrough, some of which remain open (such as opening 18) while others are filled with metal in the final processing (such as the opening 20). The individual laminates may have conductive paths 22 thereupon, which are connected to the integrated circuit 16 with fine wires 24. (The laminate structure of Figure 1 Is meant to be exemplary, and the present invention is not limited to the preparation of laminates of this or any other particular form.) Before the integrated circuit 16 and the wires 24 are attached to the package 10, the laminates 12 are consolidated by pressing the green sheets to increase their densities to about 60-65 percent of theoretical density, and then sintered to increase their densities to about 96 percent of theoretical density. The pressing to achieve 60-65 percent of theoretical density has previously been accomplished with a rigid tool whose surface is a mirror image 10, or with us Patent 4,636,275 of an upper surface 26 of the package a fluid-filled bladder as discussed In disclosure

9 whose is incorporated by reference. The present approach also deals with the pressing operation, but provides an alternative approach.

In accordance with this aspect of the invention, apparatus for fabricating an integrated circuit package from a plurality of layers of laminates comprises a porous base upon which the laminates are stacked to form a stack having an upper surface; a pressurizing tool having a cavity therein disposed in a facing relationship to the upper surface of the stack of laminates; a solid pressurizing medium including a body made of Sorbothane which is retained in the cavity of the pressurizing tool by a latex diaphragm; a pressure transfer membrane overlying the stacked laminates, transfer membrane havina a first laver the pressure adjacent the laminates made of silicone rubber and a second layer adjacent the pressurizing medium made of urethane rubber; and a pump communicating with the porous base to remove air from the space between the membrane and the stack of laminates.

is V Referring to Figure 2, an apparatus 30 for fabricating an integrated circuit package has a base 32 upon which rests the stack 14 of laminates 12, prior to consolidation by pressing. The base 32 Is made of a porous material such as sintered stainless steel having continuous porosity. The base 32 rests upon a support 34 having an evacuation line 36 therein leading to a vacuum pump 38. The edges of the porous base 32 are sealed against air loss and the gap between the base 32 and the support 34 Is similarly sealed with a sealant 40 such as glass, epoxy, or metal. Operation of the pump 38 therefore removes gas from the region of the stack 14, In the manner to be discussed subsequently.

A pressurizing tool 42 fits over the base 32, and is sealed thereto by a sliding O-ring 44. The tool 42 is generally In the form of a block of metal 46 having a cavity 48 therein. The cavity 48 is laterally dimensioned to be sufficiently larger than the lateral dimensions of the base 32 so that the tool 42 can fit over the base 32. A removable clamping fitting 50 is attached to the underside of the block of metal 46 with any convenient fastener, such as a series of bolts 52.

A block of a solid pressurizing medium 54 is contained within the cavity 48. The solid pressurizing medium 54 is preferably made of SorbothaneTM elastomeric material, which Is manufactured by Sorbothane, Inc., 2144 State Route 59, Kent. Ohio. SorbothaneTM material Is patented, and Its composition and structure are disclosed in US Patent 4,346,205, whose disclosure

Is hereby Incorporated by reference. Briefly, according to the 1205 patent the elastomeric material Is a flexible polyurethane of essentially linear structure containing unsatisfied hydroxyl groups, and having a compression set less than 15 1 percent, an elongation at break of at least 500 percent, and a recovery which is delayed after compression by at least 0.7 seconds. The elastomer is produced by reacting substantially linear polyols based on polyalkylene glycol with an average molecular weight in the range of 600 to 1200, and an aromatic diisocyanate. SorbothaneTM has been used as an energy absorbing material previously as described In the '205 patent, but no prior use like that of the present Invention Is known.

SorbothaneTM elastomeric material Is a solid, but can be deformed around the stack 14 to apply a quasi-hydrostatic pressure when confined In a volume such as defined by the walls of the cavity 48, the upper surface 26 of the stack 14, and the base 32. A typical pressure level is about 500 pounds per square inch, although the pressure can be varied widely as necessary. Although the SorbothgneTM material compresses somewhat at such a pressure level, the volume change Is relatively small and acceptable. Such pressure Is created by forcing the pressure tool 42 downwardly in the view of Figure 2. When the pressure is removed, the SorbothaneTM material returns to substantially the same shape as It had prior to deformation. During the pressing operation, the entire apparatus 30 Is heated to a temperature of about 700C by a resistance heater 56 that is placed around the apparatus. The SorbothaneTM material retains the previously described properties at this slightly elevated temperature.

Although the SorbothaneTM material can deform and then return to its original shape, It remains a solid throughout the entire operation.

The solid SorbothaneTM material Is to be distinguished from a fluid, whether a liquid or a gas, which changes shape to fill a container (or a portion of a container in the case of a liquid) even in the absence of an applied force. The SorbothaneTM material cannot leak even when holes are present in a covering layer, as it remains a solid at all times. This distinction between the solid SorbothaneTM material and a fluid is important, because the SorbothaneTM material is not subject to the leakage problems inherent In the use of fluids in pressing applications.

Other solid materials with similar properties can be used. For example, urethane blocks can be used as the pressurizing medium 54. Highly compressible foams would normally not be acceptable, as the volume change during pressurizing would not permit the tooling to function properly.

The SorbothaneTM material solid pressurizing medium 54 is held in place within the cavity 48 by a flexible, deformable diaphragm 58, whose edges are captured between the block of material 46 and the fitting 50. The diaphragm 58 is preferably formed of a sheet of natural or artificial latex rubber. A sheet about 0.015 inches thick has been found satisfactory. Latex rubber is preferred for the diaphragm 58 because it deforms around the stack 14 and can be stretched extensively without failure during pressing. When the pressure is removed, it returns to its original flat diaphragm shape as the SorbothaneTM material of the pressurizing medium 54 returns to its original shape, and continues to retain the pressurizing medium 54 in the cavity 48. The latex diaphragm 58 may be locally pierced, as by pinholes or tears, during its use over a period of time. Such damage is fully acceptable as long as the solid pressurizing medium 54 continues to be held in place. Because the pressurizing medium is a solid, no liquid containment function of the diaphragm 58 -14 is required.

A pressure transfer membrane 60 is placed over the stack 14, between the upper surface 26 of the stack 14 and the pressurizing medium 54. Preferably, the membrane 60 is draped over the stack 14 in the manner illustrated in Figure S. The membrane 60 is not captured between the block 46 and the fitting 50 as is the case for the diaphragm 58. The draping of the membrane 60 permits it to move laterally to readjust its position as the pressure is applied to the upper surface 26 of the stack 14 through the pressurizing medium 54.

Also as illustrated in Figure 3, the pressure transfer membrane 60 is preferably formed of two layers of deformable material, a first layer 62 that contacts the upper surface 26 of the stack 14 of laminates 12, and a second layer 64 that is between the first layer 62, and the diaphragm 58 and pressurizing medium 54. The first layer 62 is preferably made of silicone rubber, and most preferably has a thickness of about 0.015 inches. The second layer 64 is preferably made of urethane rubber, and most preferably has a thickness of about 0.015 inches.

The first layer 62 acts as a release layer, to prevent adherence between the pressure transfer membrane 60 and the upper surface 26 of the laminates 12. Silicone rubber is well known in the industry, and is available commercially in sheets of various thicknesses. It is generally formed by cross linking of silicones with groups such as organic peroxides. The silicones are linear polymeric structures derived from siloxanes by substitution of an organic group such as the methyl group for the oxygen atoms of the siloxane above and below the silicon atom. Chlorine or other halogens are often commonly included. For the present 1 application, silicone rubber has the important property that it has little stickiness or tack against laminate materials such as aluminum oxide laminates. Thus, with a first layer 62 of silicone rubber present, there is no sticking of any of the overlying layers or structure to the upper surface 26 of the laminates 12. Silicone rubbers do not deform extensively without formation of pinholes, but pinholes are acceptable in the present use as long as the essential separation function is retained.

The second layer 64 acts as a barrier between the diaphragm 58 and the pressurizing medium 54, on the one hand, and the upper surface 26 of the laminates 12 on the other. Urethane rubber, the preferred material, is well known in the industry. The urethane rubber is formed from polyurethane, the linear condensation polymer that can be made by the reaction of a diisocyanate and a dihydric alcohol.

The polyurethanes are characterized by the presence of the urethane group (-NHCOO-) in the polymer. The urethane rubbers are very elastic and flexible, and can deform to a great extent and over many cycles without formation of holes or tears. Urethane rubbers also have the property that they are typically slightly tacky against ceramic materials such as the aluminum oxide laminates. The first layer 62 separates the urethane rubber from the upper surface 26 of the laminates 12 so that the urethane rubber does not adhere to the ceramic material and damage it when the pressure is released. Latex rubbers are not preferred for the second layer 62 because they tend to fatigue and form holes during repeated cycles of operation.

Silicone rubbers are not preferred for the second layer 62 because they are not sufficiently elastic.

The pressure transfer membrane 60 as described herein has been found to be particularly advantageously employed in the present apparatus 30. It can deform into openings 20 as small as about 0.020 inches or smaller to prevent closure of the openings during pressing. The combination of the pressure transfer membrane 60 and the pressurizing medium 54 has been found not to round the edges of openings such as the openings 18 and 20 during the pressing operation, an important advantage that aids in maintaining precise geometries during the pressing and subsequent sintering operations.

To prepare a package using the approach of the invention, the stack 14 of unconsolidated laminates is first prepared using known techniques. (The preparation of the laminates themselves does not form part of the present invention.) The stack 14 is then placed into the apparatus 30 of the invention with the membrane 60 in place draped over the stack 14, and the apparatus is closed by placing the pressurizing tool 42 over the base 32. The interior of the apparatus is preferably evacuated with the vacuum pump 38 in the manner previously described, so that the interior has a slight A high vacuum is not required, as the of the vacuum is simply to ensure that of gas do not remain between the laminates or between the pressure transfer membrane 60 and the laminates. Such bubbles could prevent consolidation or bonding. The pumping operation could be omitted in some circumstances, although it is preferred.

The block 46 is pressed downwardly with a sufficient force to create the desired pressure in the interior of the apparatus and simultaneously heated. A preferred combination of temperature and pressure for the consolidation of aluminum oxide laminates are 700C and 500 pounds per square vacuum. purpose bubbles inch. After about 10-15 seconds, the pressure is released and the partially consolidated stack 14 removed. The elevated temperature pressurizing treatment increases the density of the laminates from about 50-55 percent of theoretical density to about 60-65 percent of theoretical density. The pressurizing treatment also causes the laminates 12 to stick together sufficiently so that the stack can be handled during the next production step.

The stack 14 is sintered according to established procedures to increase the density to about 96 percent of theoretical density. (The treatment does not form part of the invention.) A typical sintering treatment of 16000C for 90 minutes, with no The package is ready for further such asadding externally accessible attachment of the integrated circuit, and final processing such as attachment of lead wires.

The present approach can be readily applied in a production setting. A plurality of bases and stacks can be prepared for processing at one time, or the stacks can be pressed one at a time. The procedure is essentially as fast as pressing with a rigid die, but is tolerant of manufacturing variations in the configuration and thickness of individual stacks of laminates. The apparatus 30, including both the solid pressurizing medium and the pressure transfer membrane, can be reused for many cycles of operation.

Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications may be made without departing form the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.

sintering present is a temperature applied pressure. processing contacts,

Claims

CLAIMS What is claimed is:

1. Apparatus for fabricating an integrated circuit package from a plurality of layers of laminates, comprising:

a base upon which the laminates are stacked to form a stack having an upper surface; a solid pressurizing medium disposed in a to the stacked laminates, the being made of a material that deforms to conform to the upper surface of the stack of laminates under pressure but which returns to substantially its undeformed state in the absence of pressure; and a pressure transfer membrane between the pressurizing medium and the upper surface of the stack of laminates that is sufficiently flexible to conform to the upper surface of the stack of laminates, the pressure transfer membrane having a first layer adjacent the laminates that does not adhere to the laminates and a second layer adjacent the pressurizing medium that prevents contact between the pressurizing medium and the laminates.

facing relationship pressurizing medium

2. including means for removing air from the space between the membrane and the stack of laminates.

The apparatus of claim 1, further

3. The apparatus of claim 1, wherein the base is porous so that air can be removed from the space between the membrane and the stack of laminates.

4. The apparatus of claim 1, wherein the 1 19- solid pressurizing elastomeric material.

medium Is SorbothaneTM

5. The apparatus of claim 1. wherein the first layer of the membrane Is made of silicone rubber.

6. The apparatus of claim 1, wherein the thickness of the first layer of the membrane Is 0.381rrirri (0.015 in-).

7. The second layer of rubber.

apparatus of claim 1, wherein the the membrane is made of urethane

8. The apparatus of claim 1, wherein the thickness of the second layer of the membrane Is 0.38lmm (0.015 in.).

9. The apparatus of claim 1, further including a pressurizing tool having a cavity therein disposed In a facing relationship to the upper surface of the stack of laminates, and wherein the solid pressurizing medium is retained In the cavity.

10. The apparatus of claim 9. wherein the solid pressurizing medium Is retained in the cavity by a diaphragm of latex rubber.

11. Apparatus circuit package from laminates, comprising:

a porous base stacked to form a stack a pressurizing disposed in a facing V for fabricating an integrated a plurality of layers of upon which the laminates are having an upper surface; tool having a cavity therein relationship to the upper 20- surface of the stack of laminates; a solid pressurizing medium including a body made of SorbothaneTM elastomeric material which is retained in the cavity of the pressurizing tool by a latex diaphragm; a pressure transfer membrane overlying the stacked laminates, the pressure transfer membrane having a first layer adjacent the laminates made of silicone rubber and a second layer adjacent the pressurizing medium made of urethane rubber; and a pump communicating with the porous base to remove air from the space between the membrane and the stack of laminates.

12. Apparatus for fabricating an integrated circuit package from a plurality of layers of laminates, comprising:

a base upon which the laminates are stacked; a pressurizing medium disposed in a facing relationship to the stacked laminates: and a pressure transfer membrane between the pressurizing medium and the stack of laminates that is sufficiently flexible to conform to the upper surface of the stack of laminates, the pressure transfer membrane having a first layer adjacent the laminates that does not adhere to the laminates and a second layer adjacent the pressurizing medium that prevents contact between the pressurizing medium and the laminates.

13. The apparatus of claim 12, wherein the pressurizing medium is a solid.

14. The apparatus of claim 12, wherein the first layer of the pressure transfer membrane is made of silicone rubber.

A t -21

15. The apparatus of claim 12, wherein the second layer of the pressure transfer membrane is made of urethane rubber.

16. Apparatus for fabricating an integrated circuit package from a plurality of layers of laminates, comprising:

a base upon which the laminates are stacked; and a solid pressurizing medium disposed in a facing relationship to the stacked laminates, the pressurizing medium being made of a material that deforms to conform to the upper surface of the stack of laminates under pressure but which returns to substantially its undeformed state in the absence of pressure.

17. A process for pressing integrated circuit packages, comprising the steps of: providing a stack of laminates to be pressed; providing a pressurizing medium adapted to press against the stack of laminates; placing a layered pressure transfer membrane to overlie at least a portion of the stack of laminates, the pressure transfer membrane having a first layer adjacent the laminates that does not adhere to the laminates and a second layer adjacent the pressurizing medium that prevents contact between the pressurizing medium and the laminates, the pressure transfer membrane being sufficiently flexible to conform to the upper surface of the stack of laminates under pressure; and applying a pressure to the pressurizing medium which is thence transferred to the stack of laminates through the pressure transfer membrane.

18. A process for pressing integrated circuit packages providing providing disposed in a laminates, the solid material surface of the which returns in the absence of pressure; placing a layered pressure transfer membrane to overlie at least a portion of the stack of laminates, the pressure transfer membrane having a first layer adjacent the laminates that does not adhere to the laminates and a second layer adjacent is the pressurizing medium that prevents contact between the pressurizing medium and the laminates, the pressure transfer membrane being sufficiently flexible to conform to the upper surface of the stack of laminates under pressure; and a pressure to the pressurizing thence transferred to the stack of the pressure transfer membrane.

comprising the steps of:

a stack of laminates to be pressed; a solid pressurizing medium facing relationship to the stacked pressurizing medium being made of a that deforms to conform to the upper stack of laminates under pressure but to substantiallv its undeformed state applying medium which is laminates through Published 1991 at The Patent Office. Concept House. Cardiff Road. Newport. Gwent NP9 I RH. Further copies may be obtained from Sales Branch. Unit 6, Nine Mile Point Cwmfelinfach. Cross Keys, Newport. NP1 7HZ. Printed by Multiplex techniques ltd. St Mary Cray, Kent.

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