CA2036169A1 - Lamination of integrated circuit packages - Google Patents

Abstract

LAMINATION OF INTEGRATED CIRCUIT PACKAGES
ABSTRACT OF THE DISCLOSURE
Laminated integrated circuit package are prepared using an apparatus and process that consolidates the package without the use of fluids and nonconforming dies. A plurally of laminates from which the package is formed are stacked on a base. A pressure transfer membrane having two layers, a silicone rubber release layer adjacent the stack and a urethane rubber separating layer, is placed over the stack of laminates. A solid pressurizing medium, preferably a body of Sorbothane retained by a latex diaphragm in a cavity in a pressurizing tool, is pressed against the pressure transfer membrane and the underlying stack to consolidate the stack of laminates. Preferably, heat is applied simultaneous 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.

Description

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..... ~ 1990 ` : : ~ LAMINATION OF INTEGRATED CIRC~IT PACXAGES
BACKGRO~ND OF T~E INVENTION
Thia lnventlon relatcs to the preparatlon of lamlnated lnte6rnted clrcult pacXsgec, and, more particularly, to the formatlon of ~uch pac~ages from - a stack of sheet~.
Integrsted clrcult~ are electronlc devlces that are eYtremely ~lnlaturlzed, ao that hundreds or even thousands of lndlvldual clrcults and actlve elements are formed on a chlp that may be only 1/2 lnch on a slde. The reductlon ln slze of such clrcults reduces their welght ~nd volume, an~ also lncreases thelr operatlng speeds because the dlstances that electrons must travel are r-~duced.
The ~ldespread adoptlon of lntegrated clrcultry hss revolutlonlzed many areas of electronlc~.
The lntegrated clrc~lts themselves are ~- extremely small and fraglle. They must therefore be packaged and protected ln a manner that permlts eYternal electrlcal connectlons to be made, and permlts the lntegrated clrcults to be handled ln a normal manner durlng the assembly and repalr of electronic devlces that may utlllze one or many ~uch packaged lntegrated clrcults.
One common approach to the packaglng of - lntegrated clrcuits 18 to mount the clrcuits on a - - ceramic substrate, whlch 18 commonly termed a npackage~ ln the lndustrg. In the earllest packages, there was a slngle layer of ceramlc. More :- 30 recently, as the lntegrated clrcults have become more compleY, the pacXsges have also become more comple~. Now, some packages are formed of two or more la~ers of ceramlc lamlnate, with varlous layers havlng openings therethrough to permlt lnterlamlnate ,-' ,`,~ ~) .
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connec~lons and 8 ~ariety of comple~ functions of the packsge ltself that augment the functlon of the lntegrated clrcult and permlt th~ varlou~ required esternal and lnternal lnterconnectlon~ and clrcult paths.
In one procedure for the preparatlon of . multllayer ceramlc pac~ages, sheet~ of unflred . ceramlc materlsl ln a plastlc blnder (termed "Breen"
ceramlc) havlng a relatl~ely lo~ denslty ~uch a~
50-~0 percent of the theoretlcal fully compacted I denslty are processed to have metalllc trace~ and i contacts thereon, cut snd ~rimmed to have the necesssry shapes, lncludlnB the openings ¦ therethrough, and then ~tacked on top of each other l 15 ln the proper sequence snd allgnment. ~ heated tool .- I havlng the proper shape of the upper surface of the ¦ flnal ceramlc package ls pressed downwardly agalnst II the surface of the st~cX, causlng the lamln~tes to consolldate to about ~0-65 percent of theoretlcal ¦ 20 density and also cau~lng the lamlnate~ to ~tlck ! I together. The compacted package is then flred at ¦ elevated temperature to lncrease the package derslty ¦ ~ to about 9~ percent of the theoretlcal densltg, whlch 1~ sufflclently strong to carry the lntegrated . 25 clrcult. The integrated clrcult 18 fa~tened to the ¦ surface of the package, electrlcal connections are made, and a protectlve cover la sealed lnto place, , , ¦ thereby complet~ng the fabrlcation of the pac~aged lntegrated clrcult.
Whlle operable, thls procedure ls subJect to process variatlons that can affect the qualltg of the flnal packaged product. It ls dlfflcult to control the dlstrlbution of pressure ln the metalllc I presslng tool, wlth the result that dlfferent ti 35 portlons of the package are compressed by dlfferent amounts. The more hlghly compressed portlons shrlnk ¦ ¦ ==9 co=pre~aed portlon~, ~ith the !l _ .
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'":' ' . _3 result that the package tend~ to warp.' Also, there msy be small item-to-ltem ~arlatlons ln the ¦ thlcknesses of the lamlnates, snd the rlgid tool ls ¦ not well sulted to adapt to such ~arlatlons.
There ha~e' been varlatlons proposed to lmprove the unlformlty of the pacXsge~ and the ablllty of the proce~alng to tolerate normal manufacturlng varlablllty. In one approacn, dlsclosed ln US Patent 4,~3~,275, the rlgld tool 18 10 replaced by a pressurized fluid. The fluld i8 enclosed ln a rubber or other elasto~er bladder that contacts the upper 6urface of the ~tack of ' lamlnates. AB the'fluid 1B pressurlzed, the bladder 18 deformed agalnst the upper surface of the ~tac~
to compress`lt.
. I ' The approach of the '27S patent solves some ',' I of the problems lnherent wlth the use of rlgld I ¦ toollng, but suffers from problem~ of lts own. The ¦ presence of a fluid requlres seals and pr'ecautlon~
¦ 20 to prevent lsa~age that would damage the lamlnates.
I If the bladder 18 too thln, plnholes appearlng durlng repeated fleslng ln use ~111 allow the fluid to leak. The leakage of flulds i~ a partlcularly l~sldlous problem, because very small plnhole leaks that cannot be readlly detected ma~ contamlnate man~
pac~ages with mlcrogr~m quantltlea of the pressurlzatlon fluld before the leak 18 detected.
The manufacturer ls then faced wlth the problem of ¦ identlfylng the contamlnated pleces or throwing away ¦ 30 enough of the pleces to be sure that no cont~mlnated ¦ pleces remaln ln the productlon lot. If the bladder , : 18 made thlck to minlmlze the chances of leakage, lt may rot conform to small openlngs ln the stack or i ma~ cause unacceptable rou~dlng of the ed8es of ! ¦ 35 openlngs. E~perlence wlth rubber bladders used ln ' other conte~ts suggests that a bladder suf~lclently thlc~ to rel~zbly contAln the presDurlzlng fluld : :"
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wlll not reach lnto ~mall vla openlng~ about -.010-0.050 lncb ln dlameter and ~111 also round the corner~ of larger openlng~. Moreover, the blsdder may capture pockets of alr around the lamlnate that prevent complete con~olldatlon. Another problem wlth bladders ls that 'he m~terlals whlch can contaln flulds are often somewhat tacky to tbe touch snd may stlc~ to the unflred lamlnates. The re~ult 18 that the p~cXage may be pulled apsrt when the 10 bladder i8 remoYed Bfter pre~slng.
In yet another approach, some manufacturers u~ing elther the rlgld tooling or fluld approsche~
have ln6erted sep~rate toollng pieces into the stack of lsmlnates. It has been found that multlple set~
of lnserts are requlr~d because of the normal m~nufacturlng varlabillty of the lamlnates, dlscus~ed prevlousl~. The lnsertlon and po~ltlonlng I of toolln~ pleces 18 a slow process that I signlflcantly lncreases the cost of the flnal 20 package by ~lowlng the throughput of the lamlnation process.
Thu~, at the present tl3e there 1B a need for an lmproved approach to the preaslng of lamlnates used ln mlcroclrcult packsges. The approach should 25 attain the advantages posslble wlth the varlous prevlously developed lamlnatlon procedures, and not , lncorporate thelr ~hortcomlng~. The present ; lnventlon fulfllls thls need, and further provldes related advantages.
Il ¦ ~ ¦ 30~ -'~MMARY OF T~E ~ ENTION
The present lnventlon provldes ~ process and spparatu~ for laminatlng mlcroclrcult packages from stsc~s of lamlnate sheets tbat have been prevlously ~' ~ patterned ~and cut t~ shape. The approach pro~lde~ a ,i.,., . . ,., 11 . '~

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¦qussl-hydrostatlc laminatlon pressure that hss been found operable to consolidate ~tacks of lamlnates havlng openlngs through laminate lsyer~ a3 small s3 0.020 lnche~, wlthout roundlng of the edges. The 5 approach acco~modate~ normal varlatlons ln lamlnate thlckne~s and quallty, 80 that only a slngle apparatus i8 required. No flulds are used, and there 18 no danger of leakage and contamlnatlon of the packages. The approach 18 operable ln a 10 productlon -context to proce~s lamlnated psckages rapldly and at low c03t.
IIn accordance wlth the lnventlon, appar~tus _ Ifor fabricatlng an lntegrated clrcuit package from a plurallty of layers of lamlnates comprlses a bace 15 upon whlch the lamlnates are stacked to form a stack havlng an upper surface; a solld pressurlzlng medlum dlsposed in a faclng relatlonshlp to the stacked lamlnates, the pressurlzlng medlum belng made of a materlal that deform3 to conform to the upper surface of the 8tack of lamlnates under pres3ure but whlch returns to sub~tantially lts undeformed ~tate ln the absence.of pressure; and a pressure transfer membrane between the pre~surlzlng medlum and the upper 3urface of the stack of lamlnates that 1~
sufflclently flexlble to conform to the upper surface of the stack of lamlnates, the pres~ure transfer membrane havln~ a flrst layer adJacent the lamlnates that does not adhere to the lamlnates and a second layer adJacent the pressurizlng medlum that 30 prevents contact between the pres~urlzlng medlum and the lamlrates.
The solid pressurlzlng medlum ls preferably a polyurethane rubber block made of SorbothaneTM
brand materlal. Such a materlal can conform to the 35 upper surface of the stack of lamlnates.
Preferably, the pressurlzlng medlum is retained by a lates dlaphragm ln a cavlty of a pres~urlzing tool ~ I

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faclng the upper surface of the stack, ~o that the pressurizlng ~edlum 18 controllably moved lnto contact wlth the stack of lamlnates and then removed.
S So~e ~terlal~ that are preaently known for u~e as the pressurlzlne medlum have a de~ree of stlcklness or ~tack~, 80 ' thst they would stlck to the surface of the stack of lamlnates ln the absence of the pressure trAnsfer membrane. The preferred pressure transfer membrane hAs two layers, the flrst la~er adJacent the stack formed of & materlal ~uch as slllcone rubber than has no tac~ and serves as a release sgent, and ~ second layer between the flr~t layer and the pressurlzlne~medlum such a~ a la~er of urethane rubber that separates the pressurlzing medlum from the lamlnate~. Each of the layers 18 about 0.015 lnches thlck ln the preferred approach, whlch 18 sufflclentl~ thln to permlt the presslng of small dlameter openlngs such as ~ias and also does not cause roundlng of the edges of lsrge or ~mall openlngs. Since the pressurlzlng medlum 18 a solld, there 18 no possiblllty of fluld leakage fro~ the apparatus onto the laminates.
It has been found that alr;bubbles tr~spped between the pressure transfer membrane and the stsck of lamlnates can prevent bondlng locally. The base of the preferred apparatus i8 therefore lntentlonally made porous, as by fsbrlcating lt from slntered stalnles~ steel. A ~acuum ls applled ~o the underslde of the base to draw 8a8 from the reglon between the lamlnates and between the lamlnates and the membrane, thereby avoldlng such local gas-lnduced delamlnatlons.
The present approach can, of course; be applled to instances whereln the solld pressurlzlng medlum 18 not tacky. In accordance wlth thi~ aspect of the lnventlon, apparatus for fabricatlng an : j ~
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lntegrated clrcult package from ~ plurallty of ¦ la~ers of lamlnates comprlses a base upon whlch the ¦ lamlnates sre stacked; and a ~olld pressurlzlng medlum dlsposed ln a faclng relatlonshlp to the ¦ 5 stacked lamlnates, the pressurlzlng medlum belng j made of a materlal that deforms to conform to the upper surface of the stack of lamlnates under ¦ pressure but whlch returns to substantl~lly lts undeformed state ln the absence of pressure.
I lOThe pressure tranafer membrane Or the present lnvention has wlde applicablllty. In accordance wlth this a~pect of the lnventlon, apparatus for _ fabrlcatlng an lntegrated clrcult package from a plurallty of la~ers of laml~ates comprlses a base upon whlch the lamlnates are stacked; a pressurlzlng medlum dlsposed ln a faclng relatlonshlp to the stacked lamlnates; and a pressure transfer membrane between the pressurlzlng medlum and the stack of lamlnates that 18 sufflclently flexlble to conform , 20 to the upper surface of the stack of lamlnates, the I pressure transfer membrane havlng a flrst layer ¦ adJacent the laminates that does not adhere to the ~ lamlnates and a second layer ad~acent the ¦ - pressurlzlng medlum that prevents contact between.
l 2S the pressurlzlng medlum and the lRmlnates.
¦ The present lnventlon also e~tends to the ¦ process for using the approach of the lnventlon to . ¦ prepare lntegrated clrcult packages from lamlnates.
, ~ In accordance wlth thls aspect of the lnventlon, a process for pressing lntegrated clrcult packages comprlses the steps of provldlng a stack of lamlnates to be pressed; prov~dlng a pressurlzlne medlum adapted to press agalnst the stack of lamlnates; placlng a la~ered pressure transfer j 1 35 membrane to overlle at least a portlon of ~he stack ¦ of lamlnates, the pressure transfer membrane havlng a flrst la~er adJacent the lamlna~e~ that does not .~, .,1 I
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-8- ' adhere to the lamlnate~ and a ~econd layer adJacent the pres~urlzl~8 medlum that prevent~ contact between the pressurlzlng medium and the lamlnates, the pres~ure tran~fer membrane belng sufflclently fle~lble to conform to the upper surface of the stack of laminates under pressure; and applylng a pressure to the pressurlzlng medlum whlch ls thence transferred to the ~tack of laminates through the pressure ~ransfer membrane. In the preferred use of lv the process, the pres6url~1ng medlum 18 a ~olld ma~erlal that deforms to conform to the upper -j surface of the ~tsck of lamlnates under pressure but whlch returns to substantlally lts undeformed state ln the absence of pressure, such as Sorbothane.
The present lnventlon thus provldes an . lmportant advance ln the fabrlcatlon of multllayered packages used to support lntegrated circults.
Packages are pressed and consolldated ln a . quasl-hydrostatlc manner that achleves unlform .. 20 presslng that leads to unlform denslty dlstrlbution, wlthout roundlng of corners and closure of small openlngs. No potentlally leaky fl~lds are used ln the presslng operatlon. The approach 18 operable ln large-scale commerclal manufacturlng operatlons.
Other features and advantaees of the lnventlon wlll be àpparent from the followlng more detalle~
descrlptlon of the preferred embodlment, ta~en in .~ con~nctlon wlth the accompanylng drawlngs, whlch lllustrate, by way of example, the prlnclples of the lnventlon.
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BRIEF DÉSCRIPTION OF T~E DRAWINGS
Flgure 1 is a slde ~ectlonal vlew of a ceramlc package;
Flgure 2 18 a slde ~ectlonal vlew of a ~ .

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_9_ presslng apparatu~: and Flgure ~ 18 a detail of Flgure 2, ~howlng the ¦ arrangement and conHtructlon of the pre~ure transfer membrane.

DETAILED DESCRIPTION OF T~E PREFERRED EMBODIMENT
Flgure 1 illustrate~ a ceramlc package 10 o~
the type that can be pressed uslng the approach of the lnYentlon. The package 10 1~ formed from a plurallty, ln thls case three, lamlnstes 12 of unconsolldated ceramlc materlal. The lamirates are formed by prepsrlng sheets of ceramlc o~ides ~uch as alumlnum o~lde and small amounts of glasa-forming I o~ldes, ml~ed wlth an or~anic blndlng materlal such ¦ as poly~lnyl butyral. A typlcal mlsture lnclude~
1 15 about 90 percent by welght of the ceramlc oYide ¦ powders and 10 percent by weight of blnder, although ¦ these relstlYe amounts may vary. The sheets ha~e a denslty of about 2.1 grams per cublc centlme-ter, as compared with a density of about 4.0 grams per cublc centlmeter for fully dense alumlnum o~lde. Thus, the sheets, termed "green~ materlal, have a denslty of Just o~er 50 percent of the theoretlcal full density of the alumlnum o~lde.
As shown in Flgure 1, the lamlnates 12 are stacked on top of esch other to form a stack 14 of lamlnates. The bottom lamlnate 18 a full sheet, to support an lntegrated clrcult 16 thereupon. The other lamlnates have openings 18 and 20 therethrough, some of whlch remaln open (such as openlng 18) whlle~ others are fllled with metal in the flnal processlng (such as the openlng 20). The lndlYldual laminates may have conductl~e paths 22 thereupon, whlch are connected to the lntegrated i clrcult 1~ w~th flne wlres 24. (The lamlnate i .
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structure of Figure 1 18 meBnt to be esemplary, and the present lnventlon 18 not llmlted to the preparstlon of lamlnates of thls or any other particular form.) Before the lntegrated clrcult 1~ snd the wlres 24 are attached to the pacXaga 10, the lamlnatea 12 are consolldated by presslng the green sheets to lncrease thelr densltles to about ~0~65 percent of theoretlcal denslty, and then slntered to lncrease thelr densltles to about 9~ percent of theoretlcal denslty. The pres~lng to achie~e 60-65 percent of theoretlcal den~lty has prevlously been accompllshed wlth a rlgld tool whose ~urfsce 18 a . mlrror image of an upper surface 26 of the package 10, or wlth a fluld-fllled bladder as dl~cus~ed ln ~S Patent 4,636,275, who~e di~clo~ure 18 lncorporated by reference. The present approach al80 deals wlth the presslng operatlon, but provlde~
an alternatlve approach.
In accordance wlth thi~ aspect of the lnventlon, apparatus for fabrlcatlng an lntegrated clrcult package from a plurallty of layers of lamlnates comprlses a porous base upon whlch the l~minates are stacked to form a stack haYlng an upper surface; a pressurlzlng tool havlng a ca~lty thereln dlsposed ln a faclng relatlonshlp to the upper surface of the stack of lamlnates; a solld pressurlzlng medlum lncludlng a bodg made of Sorbothane whlch ls retained ln the cavlty of the pre~surlzlng tool by a lateY dlaphragm; a pre6sure transfer membrane overlylng the ~tacked lamlnates, the pressure transfer membrane havlng a flrst layer ¦adJacent the lamlnates made oY slllcone rubber and a ¦second layer adJacent the pressurlzlng medlum made ¦35 of urethane rubber; and a pump communlcatlng wlth lthe porous base to remo~e alr from the space between L =,~

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:, Referrlng to Flgure 2, sn appsratus 30 for fabrlcatlng an lntegrated clrcult packsge ha~ ~ ba~e 32 upon whlch rest~ th~ stsck 1~ of lsmlnate~ 12, prlor to consolldstlon by pres~lng. The basa ~2 1 msde of a porous materisl ~uch ~ alntered ~tslDle~
steel hs~lng contlnuous por(Jslty. The base 32 rests upon a support 34 hsYlng an e~scuatlon llne 3~
thereln lesdlng to a ~acuu~ p~mp 38. ~he edges of the porous base 32 are ~esled agalnst alr los~ and I ` 10 the gsp between the bsse 32 and the ~upport 34 is ¦ slmllarly sealed wlth a ~eslsnt 40 such as gl~s~, eposg, or metsl. Operatlon of the pump 38 therefore I removes gas from the reglon of the stac~ 14, lr. the ¦ manner to be discussed ~ubsequentl~.
A pressurlzing tool 42 flt~ over the base 32, and ls sealed thereto b~ ~ slldln~ O-ring 44. The tool 42 i8 generally ln the for~ o~ B bloc~ of metsl 1 4~ ha~lng a caYlty 48 thereln. The csvlt~ 48 ls I lsterally dlmensloned to be sufflclently larger than . 20 the lsteral dlmenslons of the base 32 80 that the tool 42 can fit over the base 32. A remoYable clamping fltting 50 18 attached to the underslde f the block of metal ~ wlth any conYenlent fastener, such as B serles of bolts 52.
A block o. a solid pressurlzlng medlum 54 ls contained wlthln the cavlty 48. ~he solld pressurlzln8 medlum 54 la preferably made of SorbothaneTM elastomerlc msterlal, whlch ls msnufactured by Sorbothane, Inc., 2144 State Route 59. Kent, Ohlo. SorbothaneTM msterlal ls patented, and its composltlon snd structure are dlsclosed ln US Patent 4,34~,205, whose dlsclosure 18 hereby lncorporated by reference. Brlefly, accordlng to the '205 patent the elastomerlc materlal ls a fle~lble polyurethane of essentially llnear structure contalnlng unsatlsfled hydro~yl groups, and havlng a compression set less than 15 . . : .. . .... .

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~12-percent, an elongatlon at break of ~t leH~t 600 percent, and a reco~ery ~hlch ls delayed after compres~lon by ~t least 0.7 ~econds. The els~tomer 1~ produced by reactlng cub~tantlally llnear pol~ols based on polyal~ylene glycol ~lth an aYerage molecular welght ln the range of 600 to 1200, and an aro~atlc dllsocyanate. SorbothaneTM ha~ been u~ed a~ an energg sbsorblng materlal prevlou~ly a~
descrlbed ln the '20~ patent, but no prlor use llke . 10 that of the present lnventlon 18 ~nown.
SorbothaneTM elastomerlc materlal 1~ a solld, but can be defor~ed around ~he stack 1~ to apply a quasl-hydrostatic pres~ure ~hen conflned ln a volu~e ~uch as deflned by the walls of the ca~ity . 15 ~8, the upper surface 26 of the ~tack 14, and the base 32. A typlcal presAure level 18 about G00 pounds per ~quare inch, although ~he pressure can be ~arled wldely as necessary. Although the SorbothaneTM materlal compre~es somewhat at such a pressure level, the ~olume change ls relatlvely small and acceptable. Such pressure ls created by forclng the pressure tool 42 downwardly 1D the vlew of Flgure 2. When the pressure 1~ removed, the SorbothsneTM materlal returns to substantlally the same shape a8 lt had prior to deform~tlon. Durlng the presslng operatlon, the ~ntlre apparatus 30 ls heated to a temperature of about 70C b~ a reslstance heater 56 that ls placed around the apparatus. The SorbothaneTM materlal retalns the prevlously descrlbed propertle~ at thls fillghtly elevated temperature.
Although the SorbothaneTM material can deform and then return to lt3 orlglnal shape, lt remalns a solld throughout the entlre operatlon.
3S The solid SorbothaneTM materlal ls to be dlstlngulshed from a fluld, whether a llquld or a gas, whlch changes shape to flll a contalner (or a l ~ l . I
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portlon of a contalner ln the cs~e of a llquld) even ln the sb~ence of sn applled force. ~h0 SorbothaneTM materlal cannot lea~ eYen ~hen holes are present in a coverlng la~er, ~ lt remsln~ a solld st all tlmes. Thl~ dl~tlnctlon b~t~een the solld SorbothaneTM msterlsl and a fluld ls lmportant, because the sorbothaneTM materlal 1 not subJect 'o the leakage proble~s lnheren~ ln the use of fluids ln pres~lng appllcatlons.
Other solid materlsl~ ~lth ~lmllar propertle~ !
¦ can be used. For e~ample, urethane block~ can be used as the pressurlzlng medium ~4. Hlghly ¦ compresslble foams ~ould normally not b~ acceptable, as the volume change durlng pressurlzlne ~ould not permlt the toollng to functlon properly.
Tbe SorbothaneT~ materlal solid I pres~urlzlng medlum 54 18 held ln place ~lthln the I cavity 48 by a fle~lble, deformable dlaphrsgm 58, ¦ whose edge~ are captured between the bloc~ of msterlal 4~ snd the flttlng 50. The dlaphragm 58 i8 ¦ preferably formed of a sheet of natural or artlflclsl lates rubber. A sheet about 0.015 lnches thlc~ hss been found satlsfsctory. Late~ rubber ls preferred for the dlaphragm 58 because lt deforms around the stac~ 14 and can be ~tretched e~tenslvel~
wlthout fallure durlng presslng. When the pre~sure ls remo~ed, lt returns to lts orlglnal flat dlaphragm shape a~ the SorbothaneTM materlal of the pressurlzlng medlum 54 returns to lts orlglnal shape, and contlnues to retaln the presfiurlzlng medlum 54 ln the cavlty 48. Tbe latex dlaphragm 58 may be locally plerced~ as by plnholes or tears, durlng its use over a perlod of tlme. Such damage ls fully acceptable as long as the solld ;35 pressurlzlng medlum 54 contlnues to be held in I,place. Because the pressurlzlng medlum 18 a solld, I L ~ ~ ~ ag= ~ ~

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Il~ requlred.
A pre~sura tran~er ~e~bran~ ~0 ls placed over the ~tack 14, betweeD the upper ~urface 2~ of the ~tack 1~ ~nd the pre~nurlzing medluM 5~.
Prefersbly, the ~embrane ~0 ln dr~ped over the 0tac~
14 ln the manner lllustrated ln Flgure 3. The membrane 60 18 not captured between the block 4~ snd the flttlng 50 as 1~ the ca~e for the dlsphragm 58.
The drsplng of th~ me~brane ~0 permlts lt to move 10 laterally to rendJust lts po~ltlon ss the pres~ure ls spplled to the upper ~urface 2~ of the stack 14 through the pres~urlzlng ~edlum 54.
Also a~ lllustrated ln Flgure 3, the pres~ure transfer membrane ~0 18 preferably formed of two lsyers of deformsble materlal, a ~lrst l~er ~2 thst contacts the upper ~urface 26 of the stack 14 of lamlnates 12, and a second layer ~4 thst lc between the first layer S2, and the dlaphrag~ 58 and pressurlzlng medlum 54. The flrst layer 62 i~
20 preferably made of slllcone rubber, and most preferably has a thlckness of about 0.015 lnches.
The second layer 64 ls preferably msde of urethsne rubber, and most preferably has a thlckness of sbout 0.015 lnches.
25The flrst layer ~2 acts as a reles~e layer, to- prevent adherence between the preasure tran~fer membrane ~0 and the upper ~urface 26 of the ,f lamlnates 12. Slllcone rùbber i8 well known ln the lndustry, and 18 avallable commercially in ~heets of 30 various thicknesses. It 18 eenerally formed by cross llnklng of silicones wltn groups such as organic peroxides. The slllcones are llnear polymerlc structures derlved from silo2anes by substltution of an organlc group such as the ~ethyl 35 group for the o~ygen atom~ of the slloxane abo~e and below the slllcon atom. Chlorlne or other halogens are ofter. commonly lncluded. For the present . L
~. .

i , .

~ 2,~g~69 appllcatlon, ~lllcone rubber ha~ the important property that lt has llttle ~tlc~lnes~ or tack agalnst laminate msterlals ~uch as aluminum o~lde lsmlnate~. Thu~, with a flr~t layer 62 of ~llicone rubber pre~ent, th0re 1~ no ~tlcklng of any of the o~erlylng layer~ or structure to the upper ~urface 26 of the lamlnates 12. Slllcone rubbers do not deform e~tenslvely wlthout formatlon of plnholes, but pinholes are acceptable ln the pre~ent u~e a~
long as the essentlal separatlon functlon ls retalned.
The ~econd layer 64 act~ as a barrler between the diaphrag~ 68 and the pres~urlzlng medlum ~4, on the one hand, and the upper surface 26 of the - 15 l~mlnates 12 on the other. Urethane rubber, the preferred materlal, 18 well known ln the lndustrg.
The urethane rubber is formed from polyurethane, the llnear condensatlon polymer that can be made by the reactlon of a dllsocyanate and a dlhydrlc alcohol.
The polyurethanes are characterlzed by the presence of the urethane group (-N~COO-~ ln the polymer. The ureth~ne rubbers are ver~ elastlc and fleYlble, and can deform to a Breat e~tent and over many cycles wlthout formatlon of holes or tears. ~rethane rubbers al80 have the property that they are typlcally sllehtly tacky agalnst ceramlc ma-~erlals such as the alumlnum o~lde lamlnates. The flrst layer 62 separates the urethane rubber from the upper surface 26 of the lamlnstes 12 80 tha~ ~he urethane rubber does not adhere to the ceramlc materlal and damage lt when the pres~ure ls released. Late~ rubbers are not preferred for the second layer 62 because the~ tend to fatlgue and form holes durln~ rspeated cycles of operation.
Slllcone rubbers are not preferred for the second layer 62 because they are not sufflclently ela~tlc.
The pressure transfer membran0 bO as ~1~' f . ~36~69 ..

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- -lb-descrlbed hereln ha~ been found to be partlcularly advantsgeou~l~ employed ln the preaent apparatu~
Q0. It can deform lnto openlng~ 20 as 8m811 as about 0.020 lnchea or smaller to preYent closure of the openlng~ durlng presslng. The comblnatlon of the pres~ure trsn~fer membrsne 60 and the pressurlzlng medlum 64 has been found not to round the edges of openlng~ such as the openlng~ 18 and 20 durlne the pre~ln8 operatlon, an lmportsnt advantage that s~d~ ln malntalnlng preclse geometrles durlng the pressin~ and sub~equent ~lnterlng operations.
To prepBre B package u~lng the appro~ch of the lnven~lon, the stack 14 of unconsolldated lamlnates 18 flr~t prepared usln~ ~nown technlquea.
(The preparatlon of th0 lamlnates themselves does not form part of the present lnventlon.) ~he stack 14 18 then placed lnto the spparatus 30 of the lnveltlon wlth the membra~e ~0 ln place draped over the ~tack 14, ard the apparatus 18 closed by placlng ! the pressurl~ing tool 42 over the base ~2. The lnterlor of the apparatus 18 prefersbly evacuated i wlth the vacuum pump ~8 ln the manner prevlously descrlbed, so that the interlor has a ~llghi vacuum. A hlgh vacuum ls not requlred, as the purpose of the vacuum 18 slmply to ensure that bubbles of gas do not remsln between the lamlnates or between the pressure transfer membrane 60 and the lamlnates. Such bubbles could prevent consolldatlon or bondlng. The pumplng operatlon could be omltted ; ln some clrcumstances, although it ls preferred.
The block 4~ 1~ pressed downwardly wlth a sufflclent force to create the deslred pressure ln l the lnterlor of the apparatus and simultaneously il 35 heated. A preferred comblnatlon of temperature and I pressure for the consolldatlon of alumlnum o~lde ¦ la=instes are 70C and 500 pounds per square i ..

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lnch. After about lO-l~ seconds, the pres~ure is released and the partially consolldated stack 14 removed. The elevated temperature pressurlzing treatment lncrea~es the denslty of the lamlnates S from about 60-5~ percent of theoretical denslty to about ~0-~5 percent of theoretlcal densltg. The pressurizlng treatment also causes the lsmlnate~ 12 to stlck together ~ufflclently 80 that the stsck can be handled durlng the ne~t production step.
The stack 14 ic sintered according to establlshed procedure~ to lncrease the den~lty to about 9~ percent of theoretlcsl den~lty. (The slnterlng treatment doeq not form part of the present lnvention.) A t~plcal sinterlng treatment 15 i8 a temperature of lhOOC for 90 mlnutes, wl-th no applled pressure. The package i8 read~ for further processing such as adding e~ternally accesslble contacts, attachment of the lntegrated clrcult, and . ~ final processlng such a8 attachment of lead wires.
The present approach can be readlly applled in a production settlng. A plurallty of bases and stacks can be prepared for prQcesslng at one time, or the stacks can be pressed one at a time. The procedure ls essentiallg a3 fast as pressing wlth B
rlgld dle, but i8 tolerant of manufacturing variatlons ln the configuration and thickness of lndividual stacks of laminates. The apparatus 30, lncludlng both the solid pressurlzlng medlum and the pressure transfer membrane, can be reused for mang cycles of operatlon.
~Although a particular embodiment of the ¦lnvention has been descrlbed-in detail for purposes Iof illustratlon, various modlflcstions mag be made Iwlthout departlng form the splrit and ~cope of the 135 lnventlon. Accordlngly, the lnvention i5 not to be ¦llmlted escept as by the appended claims.

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Claims (18)

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 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.

2. The apparatus of claim 1, further including means for removing air from the space between the membrane and the stack of laminates.

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 solid pressurizing medium is SorbothaneTM
elastomeric material.

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 about 0.015 inches.

7. The apparatus of claim 1, wherein the second layer of the membrane is made of urethane rubber.

8. The apparatus of claim 1, wherein the thickness of the second layer of the membrane is about 0.015 inches.

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

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 lagers 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 tranfer 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, comprising the steps of:
providing a stack of laminates to be pressed;
providing a solid pressurizing medium disposed in a facing relationship to the stacked laminates, the pressurizing medium being made of 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:
placing a layered pressure transfer membrane to overlie at least a portion of the stack of laminates, the pressure transfer membrane having s 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.