United States Patent
`
`4,882,212
`[11] Patent Number:
`SinghDeo et al.
`[45] Date of Patent:
`Nov. 21, 1989
`
`[191
`
`
`
`65/43
`428/428
`428/632
`501/32
`501/154
`...... 174/68.5
`174/52 FP
`... .. .. 252/513
`.. 156/62.2
`. .. ... . .. 29/840
`....................... 174/52 FP
`
`4,293,325 10/1981 Chirino et al.
`4,299,887 11/1981 Howell .
`4,491,622
`1/1985 Butt .... ..
`4,532,222
`7/1985 Butt ..
`4,569,692 2/1986 Butt ................ ..
`4,598,167
`7/1986 Ushifusa et al.
`.
`4,622,433 11/1986 Frampton ........
`4,657,699 4/ 1987 Nair . ..... ....
`4,659,404 4/1987 Butt .... ..
`4,682,414 7/1987 Butt .. ... .. .. .
`4,761,518
`8/1988 Butt et al
`
`Primary Examiner——Ellis P. Robinson
`Assistant Examiner-—P. J. Ryan
`Attorney, Agent, or Firm--Gregory S. Rosenblatt; Paul
`Weinstein
`~
`
`[57]
`
`ABSTRACI‘
`
`The present invention is directed to components and the
`process of forming the components for housing semi-
`conductor devices. The components are formed of a
`unique ceramic-glass-metal composite material com-
`prising ceramic particles, metallic particles and a glass
`matrix with said ceramic and metallic particles dis-
`persed throughout. Metal elements can be embedded
`into the material to enable simplified fabrication of de-
`vices such as semiconductor packaging.
`
`29 Claims, 3 Drawing Sheets
`
`[54]
`
`[75]
`
`[73]
`
`[21]
`
`[22]
`
`[51]
`[52]
`
`[53]
`
`[55]
`
`ELECTRONIC PACKAGING OF
`COMPONENTS INCORPORATING A
`CERAMIC-GLASS-METAL COMPOSITE
`
`Inventors: Narendra N. SinghDeo, New Haven;
`Deepak Mahulikar, Meriden, both of
`Conn.; Sheldon H. Butt, Godfrey, Ill.
`
`Assignee: Olin Corporation, New Haven,
`Conn.
`
`Appl. No.: 924,970
`
`Filed:
`
`Oct. 30, 1986
`
`B32B 1/04; H01L 23/28
`Int. Cl.‘
`U.S. Cl. ..................................
`428/76; 428/209;
`428/210; 428/323; 428/328; 428/325; 428/329;
`428/330; 428/331; 428/428; 428/432; 428/433;
`428/704; 428/901; 428/212; 428/698; 501/32;
`501/76; 357/72; 357/78; 357/81; 174/68.5
`Field of Search .................. .. 501/76, 32; 428/428,
`428/432, 901, 209, 210, 323, 328, 325, 329, 330,
`331, 433, 704, 76, 212, 698; 357/72, 73, 81;
`174/68.5
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,781,457 12/1973 McKerreghan ................ 174/52 PE
`4,002,799
`1/1977 Dumesnil et al.
`501/76
`4,186,023
`1/1980 Dumesnil et al. ..................... 106/19
`
`
`
`
`
` .
`
`
`
`000001
`
`AVX CORPORATION 1007
`
`000001
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`AVX CORPORATION 1007
`
`

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`U.S. Patent
`
`Nov. 21, 1989
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`Sheet 1 of 3
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`4,882,212
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`U.S. Patent
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`Nov. 21, 1989
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`Sheet 2 of3
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`U.S. Patent
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`Nov. 21, 1989
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`Sheet 3 of3
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`2
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`4,882,212
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`1
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`4,882,212
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`2
`vention overcomes this problem by combining metallic
`particles with the ceramic particles and glass to enhance
`the flow of the composite within the mold.
`The composite may be formed of a combination of
`materials such that it is either electrically conductive or
`non-electrically conductive. Also,
`the coefficient of
`thermal expansion may be regulated in accordance with
`the requirements of the specific application.
`A composite having a low coefficient of thermal
`expansion, while being non-electrically conductive, is
`particularly useful in the electronics industry. Presently,
`low expansivity materials are widely used in the micro-
`electronic industry as substrate materials for semicon-
`ductor packages, hybrid circuit packages and chip car-
`riers. These materials are particularly useful when the
`coefficient of thermal expansion (CTE) of the substrate
`is critical, i.e. when silicon chips or low expansivity
`leadless chip carriers are mounted directly to the sub-
`strate.
`
`Alumina ceramics are presently the most widely used
`substrate material. There is a moderate mismatch be-
`
`tween the coefficients of thermal expansion of alumina
`and the silicon chip. This mismatch does not usually
`generate unacceptably high stresses on a chip mounted
`to an alumina substrate when they are subjected to
`thermal cycling. This degree of CTE mismatch is usu-
`ally acceptable even when the chip sizes are relatively
`large or when the chip is rigidly adhered to the sub-
`strate. Alumina ceramics are particularly attractive
`since they are less costly than most other low expansiv-
`ity substrate materials. However, there are a number of
`drawbacks to alumina ceramics made in the conven-
`tional way such as poor tolerance control, poor thermal
`conductivity, i.e. in the range of about 10 to about 20
`watts per meter kelvin, and manufacturing capabilities
`limiting alumina substrate areas to less than about 50 sq.
`m.
`
`Conventional ceramic products, and ceramic sub-
`strates in particular, may be manufactured in accor-
`dance with the following procedure. Powders of alu-
`mina or other ceramic materials are mixed together
`with glass powders and organics. In the conventional
`“green tape” or “cold press” processes, the organics are
`two phase mixtures consisting of a solvent, such as
`terpineol, and a solute, such as polymethylmethacryl-
`ate. This particular solvent—solute mixture is exemplary
`and other organic mixtures may be used in their place.
`The organic mixture forms a paste or slurry when
`mixed with the mixture of glass and ceramic powders.
`The.solute:solvent ratio and the type of organic mix-
`ture, is selected in accordance with the paste rheology
`desired for the particular. application,
`i.e. the “green
`tape” or the “cold press” process.
`In the green tape process, a controlled amount of
`slurry is placed between two sheets of plastic. The
`slurry, sandwiched between the plastic sheets, is passed
`through a rolling mill to attain a consistent thickness.
`The sheets of material are then cut or punched into
`desired shapes for firing. In the cold press process, the
`glass and ceramic powders are mixed with a lower
`percentage of solvent, as compared with the green tape
`process. The mixture of glass, ceramic and organics is
`then pressed into a desired shape and fired.
`The organics,
`in either process, are volatilized at
`substantially lower temperatures than the firing or pro-
`cessing temperature of the ceramic bodies or ceramic
`substrates. The solvents usually evaporate at tempera-
`tures below about 100° C. and the solutes evaporate at
`
`ELECTRONIC PACKAGING OF COMPONENTS
`INCORPORATING A CERAMIC-GLASS-METAL
`' COMPOSITE
`
`While the invention is subject to a wide range of
`applications, it is especially suited for use as a fabricat-
`ing component for semiconductor chips individually or
`in groups. The invention discloses the bonding together
`of ceramic particles to form a coherent composite with
`desired properties which may be specfically tailored for
`specific applications in the packaging of electronic com-
`ponents.
`This application relates to U.S. Pat. No. 4,569,692,
`entitled LOW THERMAL EXPANSIVITY AND
`HIGH THERMAL
`CONDUCTIVITY SUB-
`STRATE, by S. H. Butt; U.S. Pat. No. 4,715,892 which
`is a Continuation-In-Part of U.S. patent application Ser.
`No. 838,866 (now abandoned), entitled CERMET
`SUBSTRATE WITH GLASS ADHESION COMPO-
`NENT, by D. Mahulikar; U.S. Pat. No. 4,743,299 enti-
`tled CERMET SUBSTRATE WITH SPINEL AD-
`I-IESION, by M. J. Pryor et al.; U.S. Pat. No. 4,748,136,
`entitled CERAMIC-GLASS-METAL COMPOSITE
`by S. Mahulikar et al.; U.S. patent application Ser. No.
`924,959 entitled PRODUCTS FORMED OF CERAM-
`IC-GLASS-METAL COMPOSITES, by N. N.
`SinghDeo et al.; U.S. patent application Ser. No.
`707,636, entitled PIN GRID ARRAY, by M. J. Pryor
`(now abandoned); U.S. Pat. No. 4,682,414, which is a
`Division of U.S. patent application Ser. No. 413,046
`entitled “MULTI-LAYER CIRCUITR ” by Sheldon
`H. Butt; U.S. patent application Ser. No. 651,984, (now
`abandoned) entitled “SEALING GLASS COMPOS-
`ITE” by Edward F. Smith, III; U.S. patent application
`Ser. No. 651,987, (now abandoned) entitled “SEAL-
`ING GLASS COMPOSI
`” by Edward F. Smith, III
`et al.; U.S. patent application Ser. No. 811,908, (now —
`abandoned) entitled “STEEL SUBSTRATE WITH
`BONDED FOIL” by Richard A. Eppler; U.S. Pat. No.
`4,712,161 entitled “HYBRID AND MULTI-LAYER
`CIRCUITR ” by Michael J. Pryor et al.; U.S. Pat. No.
`4,821,151, entitled “A HERMETICALLY SEALED
`PACKAGE” by Michael J. Pryor et al.; U.S. Pat. No.
`4,771,537, entitled “A METHOD OF JOINING ME-
`TALLIC COMPONENTS” by Michael J. Pryor et al.;
`U.S. Pat. No. 4,696,851, entitled “HYBRID AND
`MULTI-LAYER CIRCUITRY” by Michael J. Pryor
`et al.; U.S. patent application Ser. No. 811,906, entitled
`“MULTI-LAYER AND PIN GRID ARRAYS” by
`Michael J. Pryor; U.S. Pat. No. 4,491,622, entitled
`“COMPOSITES OF GLASS-CERAMIC
`TO
`METAL SEALS AND METHOD OF MAKING
`THE SAME” by Sheldon H. Butt; and U.S. Pat. No.
`4,725,333, entitled “METAL-GLASS LAMINATE”
`by Charles J. Leedecke et al.
`,
`In the past, glass-ceramic composites have been
`formed by one-step processes into complex shapes as
`described in U.S. patent application Ser. No. 811,906.
`This technique proved effective for many applications.
`However, as the final product had a more complex
`shape, the higher pressure required to form the compos-
`ite within the mold resulted in the molten glass between
`the ceramic particles being squeezed out and interlock-
`ing of ceramic particles. The result is a retardation of
`further flow so that the densification and shaping of the
`composite to the desired final configuration requires
`more pressure or may not be possible. The present in-
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`4,882,212
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`3 ,
`temperatures below about 450° C. The loss of the solute
`and solvent leaves pores in the green tape or cold
`pressed body. At the peak firing temperatures (approxi-
`mately 1600° C. for the conventional ceramics or ap-
`proximately 900° C. for the low fired ceramics), the
`glassy phase melts, a certain amount of sintering of the
`alumina particles occurs, and there is a resulting densiti-
`cation of the bodies. The fired substrates, being devoid
`of any connected pores, produce a hermetic substrate
`that allows an extremely limited quantity of gaseous
`penetration (< 1 X 10-3 cc He/sec). The latter charac-
`teristics of the fired substrates make them particularly
`suitable for fabricating hermetically sealed, semicon-
`ductor enclosures.
`The densification, however, causes a great deal of
`shrinkage, amounting to as much as 17% in the linear
`dimension. It is thus unrealistic to economically pro-
`duce finished parts which have better than about il%
`tolerance in the linear dimension. Therefore, dimen-
`sional tolerances for the standard fired ceramic sub-
`strates is typically quoted by ceramic manufacturers to
`be 11%. Tighter dimensional tolerances are considera-
`bly more expensive so as to offset the yield loss.
`The electronic industry is seeking higher levels of
`automation in their factories. The automatic machines
`are generally capable of positioning parts, such as the
`previously described substrates, to a much tighter toler-
`ance than il% of the linear dimension of the part. In
`fact, the tolerance of the ceramic part is, in most cases,
`the limiting factor in attaining the desired level of auto-
`mation.
`
`The present invention provides a unique method of
`manufacturing structures of ceramic-glass-metal to their
`final configuration in a one-step process by conven-
`tional means at temperatures well below the firing tem-
`perature of either the conventional ceramics, i.e. about
`1600' C., or even “low fired ceramics”, i.e. about 900°
`C. The present process also imparts unique properties to
`the manufactured product because organics are not
`necessarily required in the manufacturing process.
`The present invention is also directed to components
`and methods of producing components for radically
`improving the CERDIP technology. Currently,
`the
`CERDIP technology utilizes a ceramic base and lid. A
`sealant, usually a solder glass, seals the package at a
`relatively low temperature, ie. about 470° C. A metallic
`leadframe resides in the sealant. The strength of the
`CERDIP seal depends on the strength of the glass seal-
`ant, the length and width of the seal, the presence of
`pores or other discontinuities and eventually the nature
`of the bond between the glass and the metallic lead-
`frame. Usually, the glass is the weakest component of
`the CERDIP package. The adhesion between the lead-
`frame and the glass sealant is relatively poor in most
`package designs. If the seals are subjected to significant
`mechanical or thermo-mechanical loading, the seal can
`readily fail. Under similar conditions, a more expensive,
`ceramic side brazed package, utilizing a metallic seal,
`would remain intact.
`
`The CERDIP designs are modified to compensate for
`their inherent weakness. They have a larger seal area as
`compared to a side brazed package of the same size. The
`result is a die cavity of reduced width as compared with
`that of the side brazed package. In instances where the
`size of the space to accomodate the package is limited,
`larger chips which cannot be fit within the reduced
`sized die cavity of a CERDIP, require mounting in a
`more expensive side brazed ceramic package. The pres-
`
`4
`ent invention can overcome this problem by separating
`the leadframe from the interior of the glass seal. The
`leadframe can be firmly affixed to the base or lid of the
`package in the manner of the side brazed package. The
`resulting superior package does not transmit stress into
`the seal from flexure of the leads which routinely occurs
`during the handling of the package. At the same time,
`the size of the die cavity may be enlarged so that the
`package competes in reliability with the sidebrazed
`package but at a much lower cost.
`The present invention is also suitable for fabricating
`multi-layer packages, such as pin grid arrays and side-
`brazed packages as disclosed in U.S. patent application
`Ser. No. 811,906.
`It is a problem underlying the present invention to
`manufacture electronic packaging for components in-
`corporating a ceramic-glass-metal composite whose
`physical characteristics can be tailored to provide spe-
`cific mechanical, electrical,
`thermal, and chemical
`properties by judicious choice.
`It is an advantage of the present invention to provide
`electronic packaging for components incorporating a
`composite and a method of forming the composite
`which obviates one or more of the limitations and disad-
`vantages of the described prior arrangements.
`It is a further advantage of the present invention to
`provide electronic packaging for components incorpo-
`rating a composite and a method of forming the com-
`posite which provides a substrate having good flexure
`strength.
`It is a still further advantage of the present invention
`to provide electronic packaging for components incor-
`porating a composite and a method of forming the com-
`posite which can produce parts with a tight tolerance.
`It is another advantage of the present invention to
`provide electronic packaging for components incorpo-
`rating a composite and a method of forming the com-
`posite which can be fired at a low temperature.
`It is yet another advantage of the present invention to
`provide electronic packaging for components incorpo-
`rating a composite and a method of forming the com-
`posite which can be inexpensively processed.
`It is a still further advantage of the present invention
`to embed a metallic element into a component formed
`of a ceramic-metal-glass composite.
`It is a yet further advantage of the present invention
`to provide electronic packaging for components incor-
`porating a leadframe embedded into a ceramic substrate
`formed of a ceramic-metal-glass composite.
`It is still another advantage of the present invention
`to provide electronic packaging for components incor-
`porating a multi-layer device fabricated from a ceramic-
`glass-metal composite having metallic elements embed-
`ded into the composite at desired locations.
`Accordingly, there has been provided components
`and the process of forming the components for housing
`semiconductor devices. The components are formed of
`a unique ceramic-glass-metal composite material com-
`prising ceramic particles, metallic particles dispersed
`throughout the composite and a glassy phase for adher-
`ing the ceramic and metallic particles together. The
`composite may be formed, in a single step, by conven-
`tional processes such as hot forging and hot pressing in
`a mold to enable simplified fabrication of semiconduc-
`tor packaging. Metallic elements can be embedded into
`the composite during the hot pressing step. The inven-
`tion is particularly adaptable to form CERDIP’s, hybrid
`packages, circuit boards and multilayer devices.
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`The invention and further developments of the inven-
`tion are now elucidated by means of the preferred em-
`bodiments in the drawings.
`DETAILED DESCRIPTION OF THE
`DRAWINGS
`
`6
`low coefficient of thermal expansion and chemical non-
`reactivity. The second material is a glass which forms a
`matrix for binding the ceramic and metallic particles
`together. Since glass is relatively fragile, it is typically
`provided at such a proportion so as to prevent a signifi-
`cant reduction of the composite strength, primarily
`provided by the ceramic particles. The glass is selected
`to_be chemically reactive with the ceramic particles as
`well as with the third material, metal or alloy particles.
`The third material is comprised of metal or alloy parti-
`cles which are dispersed throughout the composite. The
`metal or alloy particles enable the ceramic particles to
`shift position, while the composite is being pressed into
`a desired shape at the processing temperature, with less
`applied pressure as compared to a ceramic-glass slurry
`alone. In addition, the metal particles improve the ther-
`mal conductivity of the composite. The metal particles
`are preferably soft and ductile. It is believed that they
`tend to mold onto the adjacently disposed surfaces be-
`tween adjacent ceramic particles so that the ceramic
`particles can slide over each other during the forming
`process without being damaged. It is believed that the
`metal particles substantially reduce the occurrence of
`interlocking between ceramic particles thereby reduc-
`ing the pressure necessary for forming the final shapes.
`The resulting composite is particularly useful in that it
`may be readily formed by a one step process into a
`complex, final shape having a very tight tolerance.
`The ceramic material typically comprises particles
`selected for their physical characteristics. The specific
`ceramic may be selected from the group consisting of
`A1203, SiC, BeO, TiO2, ZrO2, MgO, AIN, Si3N4, BN
`and mixtures thereof. The present invention is not lim-
`ited to these ceramics and may incorporate any desired
`ceramic or mixture of ceramics. The ceramic particles
`are present in a range of from about 20 to about 80
`volume percent of the final fired composite and in a
`preferred range of from about 4-0 to about 65 volume
`percent. The ceramic particles can have any desired
`shape and have an average diameter of over about
`1
`micron, preferably, between about 1 to about 200 mi-
`crons and most preferably, between about 40 to about
`100 microns. The factors considered in selecting the
`desired ceramic include its dielectric constant, its coeffi-
`cient of thermal expansion, its strength and chemical
`durability.
`Conventionally, ceramics have been chosen for their
`high temperature capabilities since their melting point is
`at a temperature between about 1300‘ to about 2500“ C.
`However, the present invention may not require the
`high temperature capabilities since the ceramic particles
`are bonded together in a glassy matrix which may have
`a relatively low softening temperature as compared to
`that of the ceramic. It is also within the terms of present
`invention to choose glasses which can be fabricated into
`components that are stable at very high temperatures.
`A second component of the composite comprises a
`glassy phase having any desired composition in accor-
`dance with the properties required by the final compos-
`ite. The glassy phase functions to bind the ceramic and
`metallic particles together within a matrix of the glass.
`An important characteristic is that the glass preferably
`is chemically reactive with both the ceramic and metal-
`lic particles. Also, it may be important that the glass has
`physical characteristics such as good chemical durabil-
`ity, high strength, an acceptable dielectric constant, and
`a softening point in a selected temperature range. Suit-
`able glasses may be selected from the group consisting
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`FIG. 1 illustrates a prior art CERDIP package.
`FIG. 2 illustrates a prior art substrate having a lead-
`frame glass bonded thereto.
`FIG. 3A illustrates a CERDIP package in accor-
`dance with the present invention.
`FIG. 3B illustrates a cross-sectional view through the
`ceramic-glass-metal substrate of FIG. 3A having the
`leadframe embedded therein.
`FIG. 4 illustrates a CERDIP package having metal 15
`coupons in the base and lid cavities in accordance with
`the present invention.
`FIG. 5 illustrates a substrate of the ceramic-glass-
`metal composite in accordance with the present inven-
`tion.
`FIG. 6A illustrates a layer of the ceramic-glass-metal
`composite with an opening extending therethrough.
`FIG. 6B is a view through section B—B of FIG. 6A.
`FIG. 7A illustrates a layer of the ceramic-glass-metal
`composite with an opening extending therethrough.
`FIG. 7B is a view through section B——B of FIG. 7A.
`FIG. 8 illustrates the components of a multilayer
`device prior to hot pressing.
`FIG. 9 illustrates the components of a multilayer
`device subsequent to hot pressing.
`FIG. 10 illustrates a semiconductor casing including a
`heat sink.
`FIG. 11 illustrates a semiconductor casing formed of
`a ceramic-glass-metal composite in accordance with the
`present invention.
`FIG. 12 illustrates a semiconductor casing of a
`ceramic-glass-metal composite including a ceramic lid.
`FIG. 13 illustrates a semiconductor casing formed of
`a ceramic-glass-metal composite and including a metal
`lid.
`FIG. 14 illustrates a semiconductor device similar to
`the embodiment of FIG. 12 but without a heat sink.
`FIG. 15 illustrates a semiconductor casing formed of
`a body of the ceramic-glass-metal composite and includ-
`ing a cup shape member which acts as a surface to bond
`the semiconductor device to as well as a heat sink.
`FIGS. 16A-16E illustrate the series of steps for form-
`ing a multilayer, ceramic-glass-metal circuit structure in
`accordance with the present invention.
`The present invention particularly relates to a com-
`posite formed of a mixture of ceramic and metal parti-
`cles bound together by a glass. The composite can be
`formed into any desired shape by techniques such as hot
`forging and hot pressing at a processing temperature
`where the selected glass is at least soft and preferably in
`the fluid condition. The resulting shaped composite is
`particularly adaptable, for example, to form substrates
`for semiconductor devices, hybrid packages, multilayer
`packages or rigid, printed circuit boards.
`The invention involves mixing together appropriate
`proportions of at least three different types of materials
`to provide selected properties. One of the materials is a
`ceramic powder which is present in a volume percent
`range selected according to the desired physical prop-
`erty requirements such as the mechanical, electrical,
`thermal and chemical properties. Typically, ceramics
`are known for their physical characteristics including
`high strength, low ductility, high dielectric constant,
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`7
`of silicate, borosilicate, phosphate, zinc-borosilicate,
`soda-lime-silica,
`lead-silicate, lead-zinc-borate glasses,
`however, any desired glass may be utilized. They may
`include phosphate glass systems having high coeffici-
`ents of thermal expansion and relatively low tempera-
`ture softening points. In addition, a vitreous or devitri-
`fled glass may be selected.
`A preferred example of a useful glass which provides
`thermosetting properties suitable for application in an
`electronic environment is a devitrified, solder glass.
`This glass is a Pb0-ZnO-B203 type glass and has a
`nominal composition of about 10 wt. % B, 0.025 wt. %
`A, 8.5 wt. % Si, 0.04 wt. % Ti, 0.01 wt. % Fe, 8.5 wt.
`% Zn, 12.5 wt. % Zr, 0.25 wt. % Hf, 2.0 wt. % Ba and
`the balance Pb. All elements are reported as wt. % of
`corresponding oxide. After the glass is liquid, it is held
`at a temperature of about 500° C. for about 10 minutes.
`The glass, upon solidification, then devitrifies. At that
`point, it will not remelt until it reaches a temperature of
`about 650‘ C. The glass is present in a range of from
`about 15 to about 50 volume percent of the fired com-
`posite and in a preferred range of from about 20 to about
`40 volume percent. The glass is preferably selected with
`a softening temperature of from about 300° to about
`1300‘ C. The processing temperature is selected so that
`the glass is at least above its softening point and prefera-
`bly is in the liquid state.
`A thermosetting composite may be formed by mixing
`the ceramic and metal particles with a glass that devitri-
`fies above a certain temperature. First, the composite is
`preferably formed at a processing temperature where
`the glass is in a liquid condition. The composite may
`then be held in an oven at approximately the processing
`temperature for a sufficient period so that it has a devit-
`rifled structure when it solidifies. When the glass is in
`the crystalline state, it is usually much stronger than in
`the vitreous state. A composite of this nature, i.e. ce-
`ramic and metal particles mixed with a devitrified glass,
`may be characterized as a thermosetting material. The
`latter characteristic is imparted because the remelting
`temperature is considerably higher than the original
`processing temperature.
`For example, a devitrifiable solder glass, CVIII man-
`ufactured by Owens Illinois Co., becomes liquid at a
`processing temperature of about 470° C. This glass as
`previously described is a PbO-Zn0-B203 type glass and
`has a nominal composition of about 10 wt. % B, 0.025
`wt. % A, 8.5 wt. % Si, 0.04 wt. % Ti, 0.01 wt. % Fe, 8.5
`wt. % Zn, 12.5 wt. % Zr, 0.25 wt. % Hf, 2.0 wt. % Ba
`and the balance Pb. All elements are reported as wt. %
`of corresponding oxide. After the glass is liquid, it is
`held at a temperature of about 500‘ C. for about 10
`minutes so that upon solidification it has a devitrified
`structure. At that point, it will not remelt until it reaches
`a temperature of about 650° C. The thermosetting char-
`acteristics of the devitrified glasses are particularly
`advantageous because they allow the final product to be
`used in a higher temperature environment than the
`original processing temperature.
`The third component of the composite comprises
`metallic particles which preferably are ductile at the
`processing temperature. The metallic particles are pro-
`vided for their ability to reduce significantly the pres-
`sure necessary to densify the final composite product. It
`is believed that they mold about the surfaces of the
`ceramic particles when they are pressed between the
`ceramic particles during the processing procedures,
`thereby reducing or eliminating interlocking of the
`
`l0
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`15
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`20
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`25
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`30
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`35
`
`45
`
`50
`
`55
`
`65
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`4,882,212
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`8
`ceramic particles so as to reduce processing pressures.
`For example, the usual processing includes heating the
`mixture of ceramic particles with the metallic particles
`and the glass to the processing temperature where the
`metal particles are soft and ductile but not molten. The
`resulting composite slurry may be formed, i.e. in a mold.
`As the ceramic-glass-metal slurry flows into the shape
`of the mold, the ceramic particles are pressed against
`each other. The glassy phase is squeezed out from be-
`tween adjacent ceramic particles providing points of
`contact. Without the presence of the metallic particles,
`the ceramic particles would remain in contact and could
`look in position thereby retarding the ability of the
`slurry to flow. The ease of flowability is required for
`densification and shaping of the composite to the de-
`sired final configuration. Any loss of flowability be-
`comes increasingly significant as the final shape be-
`comes more complex.
`A unique aspect of the present invention is the addi-
`tion of metallic particles into the composite to signifi-
`cantly affect the flowability of the composite slurry.
`The metallic particles act sort of as a lubricant to enable
`the ceramic particles to slide over each other. It is be-
`lieved that some of the metallic particles move into the
`interstices between adjacent ceramic particles and mold
`onto the ceramic particles at the points of contact which
`could interlock. It is believed that the metallic particles,
`being squeezed by the ceramic particles moving
`towards each other, adhere to the ceramic particles and
`then deform. This deformation enables the slurry con-
`taining the ceramic particles to move and flow, i.e. in a
`mold, while preventing damage to the ceramic parti-
`cles.
`The metallic particles may be constituted of any
`metal or alloy which does not melt at the processing
`temperature of the composite. Preferably, the metals
`and alloys are selected from the group consisting of
`aluminum, copper, iron, silver, gold, stainless steel and
`alloys thereof. Preferably, the selected metals and alloys
`are ductile at the processing temperature. Since any
`metal or alloy is ductile slightly below its melting tem-
`perature and below its solidus, respectively, a suitably
`selected processing temperature enables the use of any
`metal or alloy which will be ductile at the latter temper-
`ature. In the case where the metal or alloy is not ductile
`enough at the processing temperature, added pressure
`may be applied during the forming process to provide
`the required deformation. The metal or metal alloy
`particles preferably have an average diameter between
`about 0.01 to about 50 microns.
`The final, fired composite may either contain the
`metallic particles dispersed continuously or discontinu-
`ously throughout
`the composite. Even in the case
`where the metallic particles are dispersed continuously,
`they do not form a matrix and are primarily subject to
`localized sintering. When the particles are dispersed
`continuously, the product would be classified as electri-
`cally conductive and when the particles are dispersed
`discontinuously the product would typically be classi-
`fied as an insulator.
`The metallic particles are present in the composite in
`an effective amount up to about 45 vol. % of the fired
`composite to enhance the flow characteristics of the
`composite at the processing temperature. Preferably,
`the metallic particles make up from about 5 to about 45
`vol. % of the composite.
`For applications where the composite is preferably
`classified as an insulator such as for electronic packag-
`
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`9
`ing components, the metallic particles are preferably
`provided in a volume percent so that they are discontin-
`uously dispersed throughout the fired composite. Pref-
`erably, the metal or metal alloy particles in this instance
`make up less than about 25 volume percent of the final,
`fired composite. More preferably, the metal particles
`make up less than about 15 volume percent of the fired
`composite. Limiting the volume percent of metallic
`particles within these ranges is believed to prevent the
`formation of a continuous metal path in the final, fired
`composite.
`.
`The final composite, even with discontinuously dis-
`persed metallic particles, exhibits improved thermal
`conductivity as compared with a composite formed
`with only ceramic particles bonded together with a
`glassy matrix. It is particularly surprising that the final
`composite having dispersed metallic particles has in-
`creased thermal conductivity since there is no corre-
`sponding increase in electrical conductivity. The reason
`for this unusual characteristic is not fully understood.
`For application where the composite is preferably
`classified as electrically conductive, the metallic parti-
`cles are preferably provided in a volume percent so that
`they are continuously dispersed throughout the fired
`composite. Preferably, the metal or metal alloy particles
`in this instance make up more than about 25 volume
`percent of the final, fired composite. More preferably,
`the metal or metal alloy particles make up from about 30
`to about 45 volume percent of the fired composite.
`Limiting the volume percent of the metallic particles
`within these rangés is believed to promote the forma-
`tion of a continuous metal path in the final, fired com-
`posite thereby providing good electrical conductivity
`as well as thermal conductivity. Such an electrically
`conductive composite is be