WO1990010308A1 - Explosively formed electronic packages and method of manufacture - Google Patents

Explosively formed electronic packages and method of manufacture Download PDF

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Publication number
WO1990010308A1
WO1990010308A1 PCT/US1990/001006 US9001006W WO9010308A1 WO 1990010308 A1 WO1990010308 A1 WO 1990010308A1 US 9001006 W US9001006 W US 9001006W WO 9010308 A1 WO9010308 A1 WO 9010308A1
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WO
WIPO (PCT)
Prior art keywords
layer
block
metal
cover
aluminum
Prior art date
Application number
PCT/US1990/001006
Other languages
French (fr)
Inventor
Prem R. Hingorany
Original Assignee
Explosive Fabricators, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US07/318,157 external-priority patent/US5022144A/en
Priority claimed from US07/360,068 external-priority patent/US5001299A/en
Application filed by Explosive Fabricators, Inc. filed Critical Explosive Fabricators, Inc.
Publication of WO1990010308A1 publication Critical patent/WO1990010308A1/en

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K5/00—Casings, cabinets or drawers for electric apparatus
    • H05K5/0091—Housing specially adapted for small components
    • H05K5/0095—Housing specially adapted for small components hermetically-sealed
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/58—Structural electrical arrangements for semiconductor devices not otherwise provided for, e.g. in combination with batteries
    • H01L23/64—Impedance arrangements
    • H01L23/66—High-frequency adaptations
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H01L2224/481—Disposition
    • H01L2224/48135—Connecting between different semiconductor or solid-state bodies, i.e. chip-to-chip
    • H01L2224/48137—Connecting between different semiconductor or solid-state bodies, i.e. chip-to-chip the bodies being arranged next to each other, e.g. on a common substrate
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H01L2224/481—Disposition
    • H01L2224/48151—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
    • H01L2224/48221—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
    • H01L2224/48225—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being non-metallic, e.g. insulating substrate with or without metallisation
    • H01L2224/4823—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being non-metallic, e.g. insulating substrate with or without metallisation connecting the wire to a pin of the item
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
    • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L24/42—Wire connectors; Manufacturing methods related thereto
    • H01L24/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L24/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/0001—Technical content checked by a classifier
    • H01L2924/00014—Technical content checked by a classifier the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/01—Chemical elements
    • H01L2924/01014—Silicon [Si]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/01—Chemical elements
    • H01L2924/01079—Gold [Au]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/095—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00 with a principal constituent of the material being a combination of two or more materials provided in the groups H01L2924/013 - H01L2924/0715
    • H01L2924/097—Glass-ceramics, e.g. devitrified glass
    • H01L2924/09701—Low temperature co-fired ceramic [LTCC]

Definitions

  • This invention in its broadest sense, relates to forming an electronic package having a body with side walls and a base made of one material and an upper surface and a cover made of another material. More specifically, this invention relates to the fabrication of aluminum microwave electronic packages in one form of the invention and more particularly to such packages which are explosively clad with a thin layer of material having a small coefficient of thermal expansion as compared to aluminum. In a second embodiment a heat conductive material such as copper is used for the body and Kovar for the upper surface and cover.
  • a third form of the invention relates to the fabrication of power hybrid and microwave electronic packages and more particularly to such packages formed from a metal matrix material to which are explosively clad with a thin * layer of monolithic material.
  • the most common metals which are being used are cold rolled steel, stainless steel, molybdenum, aluminum, copper, glidcop (dispersion hardened cooper) , and Kovar (a well-known iron-nickel- cobalt alloy) .
  • the most popular and heretofore technically advantageous metal with which to build a microcircuit package is Kovar.
  • the normal Kovar package is a box-shaped enclosure comprising a single piece side wall that is high-temperature brazed to the package bottom. Alternatively, the bottom and side wall are stamped from a single sheet of Kovar material. Lead holes are then drilled or punched into the bottom, e.g.
  • the leads also most commonly made of Kovar, are glass-sealed into the package to complete the assembly.
  • the glass serves both to insulate the leads from the body and to form a hermetic seal.
  • this type of package is fabricated by epoxying or soldering the ceramic substrate containing the semiconductor devices to the bottom of the package, wiring the thick film metal tracks to the leads, as required, and hermetically welding a Kovar lid to the side walls to seal the package.
  • This assembly known as a hybrid microcircuit, can then be soldered onto a printed wiring board and used similarly to an ordinary discrete microcircuit containing only a single semiconductor device.
  • the advantage of a hybrid microcircuit is a decrease in weight and volume over the equivalent number of discrete devices.
  • the main advantage of using Kovar for the package is that its coefficient of thermal expansion is similar to both the ceramic substrates and the glass seals. Consequently, the complete assembly expands and contracts at the same rate. In addition to this advantage, no excessive thermal stresses are developed in the parts of the assembly during the temperature extremes encountered during fabrication and subsequent environmental testing. Unless thermally matching materials are employed, damage from thermally induced stress occurs, such as the cracking of substrates, glass seals, weld joints, and braze joints, resulting in loss of hermeticity. Hermeticity and internal atmosphere requirements, and the proscription against loose internal particles are the main reasons metal packages are chosen over ceramic or plastic type packages.
  • metal packages can be sealed in a conventional seam sealing machine which ensures control over the internal atmosphere of the package.
  • Kovar has a low thermal conductivity.
  • the use of Kovar in microcircuit packages is, therefore, limited to the packaging of low power semiconductor devices.
  • the maximum electrical power a Kovar package can dissipate is approximately one watt per square inch without overheating the housed semiconductor device and adversely affecting its electrical characteristics.
  • Metals with higher thermal conductivity, like cold rolled steel, molybdenum, aluminum, and copper are, therefore, often used for constructing hybrid microcircuit packaging for high power semiconductor devices.
  • copper is the only practical material with high enough thermal conductivity to dissipate the heat generated by several high power semiconductor devices packaged as densely as they typically are in a hybrid.
  • copper has disadvantages which must be considered if it is used as hybrid package material.
  • any force which causes stress in excess of the material's yield strength will cause a permanent physical deformation of the part. Such deformation can cause
  • annealed copper can only be strengthened by hardening through cold working of the copper, which is not practical with
  • Bryllium can be added to the copper to make it hardenable by a heat treating process, but even adding a small amount of beryllium reduces the advantage of the material in the first place. Finally, hermetically sealing a lid to a copper bodied package
  • Equipment for perimeter, or seam sealing can be used for soldering, but in order to localize the heating, a lid of low thermal conductivity and high electrical resistance, such as
  • the first sometimes referred to as a non-expansion controlled package, includes a thermally conductive body and integral side walls made from the materials like
  • 35 copper, glidcop, etc. These packages typically exhibit a coefficient of thermal expansion much higher (approximately 16 pp /deg. C) than that of the ceramic cards (approximately 7 ppm/deg. C) .
  • This copper package configuration has the major disadvantage of not having a suitable top surface for seam welding a lid in place to ensure a strong hermetic device without the risk of internal contamination. Consequently, the side walls usually require attaching along their perimeter of a thin skin or a seal ring of high electrically resistant material, like Kovar, stainless steel, or cold rolled steel, to permit seam sealing to a similar high resistance material cover by a conventional resistance welding technique.
  • a seal ring is a thin window-frame shaped piece of metal which is attached to the top of the copper side wall to provide a low thermal conductivity welding surface.
  • a second prior art approach is to low- temperature braze a side wall of low thermal conductivity metal onto a copper bottom.
  • This type of package defined as quasi-expansion controlled, consists of a thermally conductive metal such as copper, glidcop, etc. with a high coefficient of thermal expansion and side walls of Kovar with a low coefficient of thermal expansion (approximately 7 ppm/deg. C) .
  • the Kovar side walls restrict the expansion of the body during temperature excursions.
  • These packages are small in size (less than 2" x 2") as the average expansion of the package does not exactly match that of the ceramic card.
  • Kovar side walls permit glass sealing of feed-throughs and ease of resistance welding the cover.
  • This configuration can be sealed in a seam sealer and does have a high thermal conductivity package bottom to remove heat generated by internal components during use.
  • the disadvantage of this configuration is the low strength of the braze joint between the side wall and the copper bottom, resulting from the low temperature braze (less than 375° C) which is necessary to ensure that the copper is not softened and weakened.
  • the difficulty with this package is similar to that of the first, in that the braze joint is between two very dissimilar materials whose thermal coefficient of expansion differences are enough to compromise the strength of the joint during thermal exposures.
  • a third category of device is defined as a controlled-expansion package where the body, consisting of materials like Molybdenum, Copper-Tungsten, etc.
  • Another type of device results from a process where a seal ring or side wall is high-temperature brazed onto the bottom member.
  • the side wall or ring can be attached with a cover in a seam sealer and the braze joint is strong enough to withstand environmental testing.
  • the disadvantage, however, of this configuration is that high temperature brazing is done well about the 375° C softening temperature of copper, and where the bottom is made of copper, its strength is compromised, causing it to yield to thermal mismatch of other materials used in the hybrid device assembly, i.e., the ceramic substrate.
  • Still another process is to machine the entire package from a solid copper piece of the required hardness and electron beam weld a thermally low conductivity ring at the rim of the package.
  • Electron beam welding due to its concentrated heat applied for a very brief time, does not soften the copper.
  • This approach even if it is performed satisfactorily, requires excessive machining and suffers from poor yields because in order to maintain required cosmetics and assurance of hermeticity, the machining of the copper package must be performed in two stages. The first stage produces an oversized rim which, after electron beam welding, is finish machined to eliminate the cavities and slag caused during the electron beam welding. Also, due to the difficulty of maintaining a consistent electron beam, frequent blow-outs occur, resulting in loss of the hermetic joint and requiring the package to be scrapped.
  • Another form of microwave electronic packages are produced from aluminum alloys due to its low weight and good thermal dissipation.
  • aluminum alloys are their high expansion which creates stress in the ceramic substrate mounted in the package which could result in cracking of the ceramic.
  • Epoxy offers sufficient compliancy but only for small packages, such as 2 H x 3" type. As the package size keeps growing, the expansion mismatch becomes unacceptable.
  • aluminum alloy packages offer significant difficulties in finally attaching a cover to the enclosures in a hermetic fashion. This is because aluminum and its alloys do not have good solderability, brazeability and weldability. Due to this same drawback, the attachment of prefabricated glass feed- throughs is also difficult which results in loss of hermeticity during manufacture or in use due to thermal fluctuations.
  • high strength aluminum alloys like 6061 T6 are machined to produce a package consisting of a base, side walls and holes drilled in the side walls for installing feed- throughs for wire leads.
  • the feed-throughs consist of a Kovar lead, with glass sealed to the inner diameter of a Kovar ring. The glass sealing in the feed-throughs electrically separates the leads from the body, as well as ensuring a hermetic seal.
  • the microwave packages are typically electroplated with silver or gold with a nickel underlayer. The electroplating serves the purpose of providing solderability/brazeability to aluminum surface and prevents the corrosion of the aluminum.
  • the carrier plates minimize the effect of expansion mismatch between the package and the ceramic card and tend to prevent the warping or cracking of the ceramic card or in some cases the detachment of ceramic card from the base of the package. This is because a aluminum and its alloys have a high coefficient of thermal expansion (22 ppm/° C.) compared to the ceramic card at 7 ppm/° C.
  • the carrier plates consisting of Kovar (7 ppm/° C.) or stainless steel (12 ppm/° C.) offer a compromise situation and hence are used as transition materials.
  • the disadvantages, of the type of carrier plates are excess weight and a significant thermal barrier as both stainless steel and Kovar are of low thermal conductivity.
  • the brazing of Kovar for the stainless steel seam sealing ring presents a problem due to voids, leaching of electroplated material at brazing temperature etc. , often resulting in leaky packages.
  • Electronic packages are usually produced from monolithic metals and alloys. The materials chosen are such that they offer reasonable compromise of thermal dissipation expansion match with ceramics, strength, reduced weight and glass sealability. In packages requiring high power dissipation or large size, these compromises are unacceptable. Such packages are then produced by choosing different metals and alloys as different components of the package and brazing them together to produce a configuration well suited to specific needs. Such packages, however suffer from poor integrity and high cost. Integrity is affected by long term unreliability of brazed joints which compromise the hermetic seal of the packages.
  • metal matrix materials are metals having non- metallic particles homogeneously dispersed through them, creating unique characteristics in the material.
  • These particles can be graphite or ceramic, such as silicon carbide, baron, nitride, etc. which are impregnated within copper and aluminum or other alloys.
  • the particles can be in fiber or particulate form.
  • the principle behind the metal matrix materials is that the non-metals or ceramics, which generally have lower coefficient of thermal expansion and in some cases higher thermal conductivity, restrict the expansion of the parent metal or alloy. The amount of non-metal or ceramic loading determines the final characteristics of the product and hence can be tailored to a specific need.
  • copper or aluminum alloys are machined to produce a package consisting of a base, side walls and holes drilled in the side walls for installing feed-troughs.
  • the feed-throughs consist of a Kovar lead, with glass sealed to the inner diameter of a Kovar or nickel-iron alloy ring. The glass sealing in the feed-throughs electrically separates the leads from the body, as well as insuring a hermetic seal.
  • the packages are typically plated with silver or gold with a nickel underlayer. The electroplating serves the purpose of providing solderability/brazeability to the packages along with offering corrosion protection.
  • the package now is ready to accept a circuit carrying ceramic card.
  • the ceramic cards are soldered or attached by epoxy onto a carrier plate of intermediate expansion prior to epoxying/soldering the carrier plate inside the package.
  • the carrier plate minimizes the effect of expansion mismatch between the package and the ceramic card and tends to prevent the warping or cracking of the ceramic card and in some cases the detachment of ceramic card from the base of the package. This is because copper and aluminum and its alloys have a high coefficient of thermal expansion (aluminum ⁇ 22 ppm/° C. and copper ⁇ 16 ppm/° C.) compared to the ceramic card at 7 ppm/° C).
  • the disadvantages of carrier plates is in additional weight and barrier to thermal dissipation.
  • a microwave package having controlled heat expansion characteristics includes a block of aluminum or aluminum alloy having a base on one side and being relieved on the opposite side to form a receptacle with a bottom and open top having a peripheral edge.
  • a first layer of material having a low coefficient of thermal expansion in comparison to the block is explosively bonding to the base of the block.
  • a second layer of material having a low coefficient of thermal expansion in comparison to the block extends across the top and is explosively bonded to the peripheral edge.
  • Feed-through openings which communicate with the receptacle can be provided either through the side wall of the block or through the second layer.
  • a cover made of the same material as the second layer extends across and is welded to the second layer.
  • a ceramic substrate is attached to the bottom of the receptacle.
  • the first and second layers can be made of Kovar and/or Invar.
  • a wire extends through each of the feed-through openings and glass can surround each of the wires and hermetically seal the wires around the respective openings.
  • a first interliner can be provided between the first layer and the base of the block and a second interliner can be provided between the second layer and the peripheral edge of the block which can be made of any one of pure aluminum, titanium, tantalum and silver.
  • the microwave package described above can be made by explosively bonding a layer of material to opposite side of a block of aluminum or aluminum alloy, each of the layers being of a material having a low coefficient of thermal expansion in comparison to the block. Machining can then be done through one of the layers so that material is removed from the block to form a receptacle therein.
  • Lead holes can be provided in the side of the block or one of the layers, the ceramic substrate can be attached to the bottom of the receptacle and feed wires can be extended through the lead holes.
  • a cover can be placed over the layer at the opening and made of the same material as the layer and hermetically sealed thereto, as by welding.
  • the block can be in the form of an elongated bar and a plurality of receptacles can be machined into the bar simultaneously or sequentially whereupon the bar can be cut between the receptacles to form separate microwave packages.
  • a hybrid microcircuit package and the * method of making it comprising a body and side walls of a material having a high coefficient of thermal conductivity, such as a copper bodied device.
  • the package also includes a seal ring, or superimposed frame, mounted on the top edge surface of the side wall structure to permit the attachment thereto of a lid or cover by traditional resistance welding techniques without overheating and softening the body material.
  • the seal ring, or welding ring is attached to the side wall of the package by the process of explosive clading which is done prior to the body material being machined into the package configuration.
  • an electronic package having metal matrix material with controlled coefficient of thermal expansion and superior thermal dissipation characteristic includes a block of metal matrix material having a base on one side and being relieved on the opposite side to form a receptacle with a bottom and top having a peripheral edge.
  • a layer of material having the required resistance or laser weldable features in comparison to the block is explosively bonded to the top peripheral edge of the block.
  • Feed-through openings which communicate with the receptacle can be provided through the side wall of the block.
  • a ceramic card carrying electronic components and circuit traces is attached to the bottom of the receptacle.
  • top explosively bonded layer can be welded to the peripheral edge of the top layer. This completes the fabrication and sealing of an electronic package.
  • the block can be in the form
  • a microwave package can be provided which has the heat conductivity of copper or aluminum but a reduced 5 coefficient of thermal expansion due to the clading of materials to opposite sides of the microwave package which have very low coefficients of thermal expansion. This minimizes the assembly and expansion problems previously described.
  • a microwave package can be provided which has the heat conductivity of copper or aluminum but a reduced 5 coefficient of thermal expansion due to the clading of materials to opposite sides of the microwave package which have very low coefficients of thermal expansion. This minimizes the assembly and expansion problems previously described.
  • an electronic package which has the properties of metal matrix materials but the weldability or joinability of conventional materials.
  • Figure 1 is a diagrammatic perspective view showing layers of material being explosively clad to a bar of aluminum or aluminum alloy; 30 Figure 2 is perspective view of the composite bar formed in Figure 1;
  • Figure 3 is an enlarged perspective view of the bar after it has been milled to form a series of receptacles; -15-
  • Figure 4 is a perspective view of one of the receptacles cut from the bar of Figure 3;
  • Figure 5 is a perspective view similar to Figure 4, but showing the feed-through openings in the side wall of the receptacle;
  • Figure 6 is an enlarged perspective view, similar to Figure 5, but showing ceramic substrates in place and the feed-through wires extending through and hermetically sealed within the feed-through openings;
  • Figure 7 is a horizontal section, taken along line 7-7 of Figure 6, showing further detail of the package;
  • Figure 8 is a perspective view of the microwave package showing the lid in place
  • Figure 9 is a fragmentary perspective view showing an alternative embodiment wherein the feed-through openings are in the layer of clad material
  • Figure 10 is a perspective view of a composite bar for manufacturing a matrix electronic package
  • Figure 11 is a perspective view of one receptacle cut from the composite bar of Figure 10;
  • Figure 12 is an enlarged perspective view, similar to Figure 11, but showing the ceramic substrates in place and the feed-through wires extending through and hermetically sealed within the feed-through openings;
  • Figure 13 is a horizontal section, taken along line 13-13 of Figure 12, showing further details of the package;
  • Figure 14 is a perspective view of the microwave package showing the lid in place.
  • a microwave package can be made which includes a body of aluminum clad with thin layers of Kovar or Invar or other material having a low coefficient of thermal expansion.
  • the average expansion of the package is a function of the volume of the individual materials which form the completed microwave package.
  • Aluminum is a good material to use because of its low weight and good thermal dispassion. However, its coefficient of thermal expansion is quite high, i.e., 22 ppm/° C.
  • Kovar a well-known commercial alloy consisting of iron-nickel-cobalt or Invar, alloy of iron-nickel, has a low coefficient of thermal expansion.
  • stainless steel has a coefficient of 12 ppm/° C.
  • a bar 10 of aluminum can be clad on opposite sides with a bottom layer 12 and an upper layer 14, which may be Kovar or Invar. These layers can vary in thickness, but a thickness of between 40 and 50 mils has been found to be satisfactory. These layers may be clad to the aluminum bar by explosive bonding under techniques well-known in the explosive bonding art. Explosives in the form of chemical powder are placed equally on both the sides of the assembly and detonated.
  • each outside material layer produces a metallurgical bond which is also hermetic in nature.
  • the use of easily bondable interliner like pure aluminum, titanium, tantalum or silver is commonly used. In this situation, a five layer composite is assembled and explosively attached.
  • the composite bar can be milled through top layer 14 so as to form a plurality of receptacles 16 so that upper layer 14 now forms a rim around the upper edge of each receptacle.
  • the machining is performed such a way that a thin layer of aluminum is left in tact under the cavity of the package.
  • the bottom layer of Kovar or Invar, as shown in Figure 3 remain unmachined and primarily adds to the overall strength of the package and restricts the expansion of aluminum.
  • the machined package is now ready for conventional electroplating and feed-through brazing/soldering.
  • the composite construction in Figure 3 can be cut between each receptacle to form separate microwave packages as shown in Figure 4.
  • Each package has a flange 18 extending from opposite sides thereof. Holes 20 can be drilled in each corner, as shown, for attachment of the microwave base within a piece of equipment.
  • the receptacle 16 has a bottom or base 22, side walls 24 and end walls 26.
  • feed-through openings 28 are drilled through side walls 24, as shown.
  • feed-through wires 30 extend through each opening 28.
  • the wires 30 can be sealed within feed-through openings 28 by means of a glass or ceramic seal 32.
  • Substrates, such as substrates 34 and 36 can be attached to the aluminum floor 22 of receptacle 16, as by adhesive in the form of an epoxy.
  • the ceramic substrate has a coefficient of thermal expansion of 7 ppm/° C. , about the same as layers 12 and 14. Although the substrates are connected to the aluminum base 22, the expansion of the base will be greatly limited by the adjacent clad layer 12.
  • cover 40 can be welded in place around layer 14.
  • cover 40 will be made of the same material as layer 14, i.e., Kovar or Invar which can be welded and hermetically sealed quite easily, as compared to aluminum.
  • FIG. 9 An alternative embodiment is shown in Figure 9 wherein the aluminum layer 10' is thinner than aluminum 10 of the previous embodiment and top layer 14' is thicker, such as on the order of 200 to 250 mils. This provides sufficient space for feed-through openings 28-" to be placed in the layer 14' rather than through the aluminum layer. With this arrangement there is less expansion of openings 28' due to thermal expansion of layer 14' than there would be with aluminum layer 10-". This makes it easier to be sure that a hermetic seal is maintained between the wires 30 and the openings 28'.
  • a further form of the invention is a process for a product having a copper base and side walls upon which is superimposed a welding ring of Kovar, although it is understood that the invention is not limited to those materials.
  • Other combinations of materials may be used, depending on the package specification, such as molybdenum or copper-tungsten as a body material and
  • Kovar as a ring material.
  • the structure for this form of the invention is substantially identical to that shown in Figures 4-8 except that receptacle 16 is copper or copper alloy rather than aluminum and bottom layer 12 is omitted.
  • a metal matrix bar 42 has a top layer 44, such as copper or aluminum, explosively clad thereto.
  • Bar 40 can be composed of a base metal which could be copper or aluminum which has graphite or ceramic particles, such as silicon, carbide, boron or nitride which are homogeneously mixed through the base metal. These particles alter the characteristics of the base metal, such as a lower coefficient of thermal expansion or increasing thermal conductivity. Also, the strength of the material can be increased. The desired characteristics can be increased by adding more of the non-metallic particles or decreased by decreasing the amount of non-metallic particles.
  • a receptacle has been constructed using 40 - 50% fill silicon carbide impregnated aluminum 6061 matrix with a layer of stainless steel bonded thereto with an inner liner of aluminum alloy between the matrix and the stainless steel layer. Portions of the bar can be milled out simultaneously or sequentially through top layer 44 to form receptacles which can be separated, as described in the previous embodiments so as to form individual receptacles, such as receptacle 46, shown in Figure 11.
  • the receptacle 46 has a bottom or base 48, side walls 50 and end walls 52. Holes 54 can be drilled in each corner of flanges 56, as shown, for attachment of the electronic package base within a piece of equipment.
  • feed-through openings 58 are drilled through side walls 50.
  • feed-through wires 60 extend through each opening 58.
  • Wires 60 can be sealed within feed-through openings 58 by means of a glass or ceramic seal 62.
  • Substrates, such as substrates 64 and 66 can be attached to the matrix floor 48 of receptacle 46, as by an epoxy adhesive.
  • cover 70 can be welded in place around layer 44.
  • cover 70 will be made of the same material as layer 14, i.e., aluminum or copper which can be welded and hermetically sealed quite easily. -20-
  • microwave package has been made which is of simple construction yet because it is made of aluminum
  • the microwave package can be made in larger sizes than heretofore possible without exceeding the expansion capabilities of the ceramic substrates placed within them.
  • the clad material is
  • the aluminum provides great thermal conductivity but the clad material limits the expansion of the aluminum material, while providing a suitable material for
  • a copper body is used, having a layer of Kovar clad thereto.
  • metal matrix material can be used which has a layer of copper or aluminum clad to the top surface.
  • the microwave package is formed by milling away a portion of this top surface to form the container.
  • a top cover is provided which is of the same material as the clad layer

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Abstract

In one embodiment, a microwave package is constructed from a block of aluminum having layers of material clad to opposite sides thereof having a lower coefficient of thermal expansion than the aluminum block. A receptacle is formed by milling away a portion of one of the layers and a large portion of the aluminum while maintaining an aluminum base or floor within the receptacle. Ceramic substrates can be attached to the floor and connected to wires which extend through feedthrough openings either in the aluminum side walls of the receptacle or through the clad material. A cover can be hermetically attached, as by welding, to the layer of clad material to complete the microwave package assembly. In a second embodiment, the receptacle is copper rather than aluminum. In a further alternative form of the invention, a metal matrix material can be used which has a layer of copper or aluminum clad to the top surface. The microwave package is formed by milling away a portion of this top surface to form the container. A top cover is provided which is of the same material as the clad layer which facilitates easy welding or attachment thereto.

Description

EXPLOSIVELY FORMED ELECTRONIC PACKAGES AND METHOD OF MANUFACTURE
Technical Field
This invention, in its broadest sense, relates to forming an electronic package having a body with side walls and a base made of one material and an upper surface and a cover made of another material. More specifically, this invention relates to the fabrication of aluminum microwave electronic packages in one form of the invention and more particularly to such packages which are explosively clad with a thin layer of material having a small coefficient of thermal expansion as compared to aluminum. In a second embodiment a heat conductive material such as copper is used for the body and Kovar for the upper surface and cover. A third form of the invention relates to the fabrication of power hybrid and microwave electronic packages and more particularly to such packages formed from a metal matrix material to which are explosively clad with a thin* layer of monolithic material.
Background Art
In the current art of building metal hybrid microcircuit packages, the most common metals which are being used are cold rolled steel, stainless steel, molybdenum, aluminum, copper, glidcop (dispersion hardened cooper) , and Kovar (a well-known iron-nickel- cobalt alloy) . The most popular and heretofore technically advantageous metal with which to build a microcircuit package is Kovar. The normal Kovar package is a box-shaped enclosure comprising a single piece side wall that is high-temperature brazed to the package bottom. Alternatively, the bottom and side wall are stamped from a single sheet of Kovar material. Lead holes are then drilled or punched into the bottom, e.g. in the familiar dual-in-line or plug-in configurations or in the side wall, e.g. in the flat pack or butterfly configuration. The leads, also most commonly made of Kovar, are glass-sealed into the package to complete the assembly. The glass serves both to insulate the leads from the body and to form a hermetic seal. Typically, this type of package is fabricated by epoxying or soldering the ceramic substrate containing the semiconductor devices to the bottom of the package, wiring the thick film metal tracks to the leads, as required, and hermetically welding a Kovar lid to the side walls to seal the package. This assembly, known as a hybrid microcircuit, can then be soldered onto a printed wiring board and used similarly to an ordinary discrete microcircuit containing only a single semiconductor device. The advantage of a hybrid microcircuit is a decrease in weight and volume over the equivalent number of discrete devices. The main advantage of using Kovar for the package is that its coefficient of thermal expansion is similar to both the ceramic substrates and the glass seals. Consequently, the complete assembly expands and contracts at the same rate. In addition to this advantage, no excessive thermal stresses are developed in the parts of the assembly during the temperature extremes encountered during fabrication and subsequent environmental testing. Unless thermally matching materials are employed, damage from thermally induced stress occurs, such as the cracking of substrates, glass seals, weld joints, and braze joints, resulting in loss of hermeticity. Hermeticity and internal atmosphere requirements, and the proscription against loose internal particles are the main reasons metal packages are chosen over ceramic or plastic type packages.
The particular advantage in using metal packages is that they can be sealed in a conventional seam sealing machine which ensures control over the internal atmosphere of the package.
The major disadvantage of Kovar, however, is that it has a low thermal conductivity. The use of Kovar in microcircuit packages is, therefore, limited to the packaging of low power semiconductor devices. The maximum electrical power a Kovar package can dissipate is approximately one watt per square inch without overheating the housed semiconductor device and adversely affecting its electrical characteristics. Metals with higher thermal conductivity, like cold rolled steel, molybdenum, aluminum, and copper are, therefore, often used for constructing hybrid microcircuit packaging for high power semiconductor devices. In some applications, copper is the only practical material with high enough thermal conductivity to dissipate the heat generated by several high power semiconductor devices packaged as densely as they typically are in a hybrid.
Use of copper in this context has disadvantages which must be considered if it is used as hybrid package material. First, its coefficient of thermal expansion is considerably different from the ceramic substrates and glass seals. An assembled microcircuit cannot be designed which expands and contracts at the same rate as the copper bodied package, resulting in an assembly having inherent thermal stresses. Second, copper has an annealing temperature of 375° C. If processed above this temperature, as typically is necessary in the high temperature brazing process utilized in the prior art, copper will change from relatively elastic to plastic, -4-
or inelastic material. Like all plastic materials, any force which causes stress in excess of the material's yield strength will cause a permanent physical deformation of the part. Such deformation can cause
05 cracked substrates and loss of hermeticity in the assembled device.
In addition to the deformation problem, annealed copper can only be strengthened by hardening through cold working of the copper, which is not practical with
10 a machined part. Bryllium can be added to the copper to make it hardenable by a heat treating process, but even adding a small amount of beryllium reduces the advantage of the material in the first place. Finally, hermetically sealing a lid to a copper bodied package
15 must be limited to a low temperature soldering or brazing process. Such a process requires care in selecting a material that either melts at a temperature low enough that does not damage the internal assemblies, or one where the process heating can be localized enough
20 to prevent exposure of the internal components of the package to excessive heating. Equipment for perimeter, or seam sealing can be used for soldering, but in order to localize the heating, a lid of low thermal conductivity and high electrical resistance, such as
25 Kovar, must be used to effect the contact resistance heating. This, of course, results in another mismatch between the lid and copper body, which will stress the weaker solder alloy causing eventual hermetic failures. Four different basic package configurations have
30 been adopted in the prior art to deal with the various combinations of problems and criteria outlined above.
The first, sometimes referred to as a non-expansion controlled package, includes a thermally conductive body and integral side walls made from the materials like
35 copper, glidcop, etc. These packages typically exhibit a coefficient of thermal expansion much higher (approximately 16 pp /deg. C) than that of the ceramic cards (approximately 7 ppm/deg. C) . This copper package configuration, however, has the major disadvantage of not having a suitable top surface for seam welding a lid in place to ensure a strong hermetic device without the risk of internal contamination. Consequently, the side walls usually require attaching along their perimeter of a thin skin or a seal ring of high electrically resistant material, like Kovar, stainless steel, or cold rolled steel, to permit seam sealing to a similar high resistance material cover by a conventional resistance welding technique. A seal ring is a thin window-frame shaped piece of metal which is attached to the top of the copper side wall to provide a low thermal conductivity welding surface.
To overcome the disadvantage of the first type of package, a second prior art approach is to low- temperature braze a side wall of low thermal conductivity metal onto a copper bottom. This type of package, defined as quasi-expansion controlled, consists of a thermally conductive metal such as copper, glidcop, etc. with a high coefficient of thermal expansion and side walls of Kovar with a low coefficient of thermal expansion (approximately 7 ppm/deg. C) . The Kovar side walls restrict the expansion of the body during temperature excursions. These packages are small in size (less than 2" x 2") as the average expansion of the package does not exactly match that of the ceramic card. Kovar side walls permit glass sealing of feed-throughs and ease of resistance welding the cover. This configuration can be sealed in a seam sealer and does have a high thermal conductivity package bottom to remove heat generated by internal components during use. The disadvantage of this configuration is the low strength of the braze joint between the side wall and the copper bottom, resulting from the low temperature braze (less than 375° C) which is necessary to ensure that the copper is not softened and weakened. The difficulty with this package is similar to that of the first, in that the braze joint is between two very dissimilar materials whose thermal coefficient of expansion differences are enough to compromise the strength of the joint during thermal exposures. A third category of device is defined as a controlled-expansion package where the body, consisting of materials like Molybdenum, Copper-Tungsten, etc. , has the coefficient of thermal expansion approximating (5-9 ppm/deg. C) that of side walls made of Kovar. The typical method of attachment of the dissimilar materials comprising the body and the side wall is brazing and as typical of brazed joints, the reliability is questionable.
Another type of device results from a process where a seal ring or side wall is high-temperature brazed onto the bottom member. In this configuration, the side wall or ring can be attached with a cover in a seam sealer and the braze joint is strong enough to withstand environmental testing. The disadvantage, however, of this configuration is that high temperature brazing is done well about the 375° C softening temperature of copper, and where the bottom is made of copper, its strength is compromised, causing it to yield to thermal mismatch of other materials used in the hybrid device assembly, i.e., the ceramic substrate.
Still another process is to machine the entire package from a solid copper piece of the required hardness and electron beam weld a thermally low conductivity ring at the rim of the package. Electron beam welding, due to its concentrated heat applied for a very brief time, does not soften the copper. This approach, even if it is performed satisfactorily, requires excessive machining and suffers from poor yields because in order to maintain required cosmetics and assurance of hermeticity, the machining of the copper package must be performed in two stages. The first stage produces an oversized rim which, after electron beam welding, is finish machined to eliminate the cavities and slag caused during the electron beam welding. Also, due to the difficulty of maintaining a consistent electron beam, frequent blow-outs occur, resulting in loss of the hermetic joint and requiring the package to be scrapped.
Another form of microwave electronic packages are produced from aluminum alloys due to its low weight and good thermal dissipation. However, one of the major disadvantages of aluminum alloys is their high expansion which creates stress in the ceramic substrate mounted in the package which could result in cracking of the ceramic. Typically, the industry uses epoxy to attach ceramic to a metal base. Epoxy offers sufficient compliancy but only for small packages, such as 2H x 3" type. As the package size keeps growing, the expansion mismatch becomes unacceptable. Also, aluminum alloy packages offer significant difficulties in finally attaching a cover to the enclosures in a hermetic fashion. This is because aluminum and its alloys do not have good solderability, brazeability and weldability. Due to this same drawback, the attachment of prefabricated glass feed- throughs is also difficult which results in loss of hermeticity during manufacture or in use due to thermal fluctuations.
In the current art of building microwave packages, high strength aluminum alloys like 6061 T6 are machined to produce a package consisting of a base, side walls and holes drilled in the side walls for installing feed- throughs for wire leads. The feed-throughs consist of a Kovar lead, with glass sealed to the inner diameter of a Kovar ring. The glass sealing in the feed-throughs electrically separates the leads from the body, as well as ensuring a hermetic seal. The microwave packages are typically electroplated with silver or gold with a nickel underlayer. The electroplating serves the purpose of providing solderability/brazeability to aluminum surface and prevents the corrosion of the aluminum. These machined and electroplated packages are then installed with feed-throughs by using 80% gold-20% tin braze alloy at 325° C. to braze the inside of the plated hole and outside of the Kovar ring of the feed- through. An electroplated seal ring consisting of Kovar or stainless steel is also brazed to provide seam sealing capability for the cover, at the same time the feed-throughs are brazed. The package now is ready to accept a circuit carrying ceramic card. In most cases, the ceramic cards are soldered or epoxied onto a carrier plate prior to epox ing/soldering the carrier plate inside the package. The carrier plates minimize the effect of expansion mismatch between the package and the ceramic card and tend to prevent the warping or cracking of the ceramic card or in some cases the detachment of ceramic card from the base of the package. This is because a aluminum and its alloys have a high coefficient of thermal expansion (22 ppm/° C.) compared to the ceramic card at 7 ppm/° C. The carrier plates consisting of Kovar (7 ppm/° C.) or stainless steel (12 ppm/° C.) offer a compromise situation and hence are used as transition materials. The disadvantages, of the type of carrier plates are excess weight and a significant thermal barrier as both stainless steel and Kovar are of low thermal conductivity. Also, the brazing of Kovar for the stainless steel seam sealing ring presents a problem due to voids, leaching of electroplated material at brazing temperature etc. , often resulting in leaky packages.
In a recent development, some package manufacturers have attempted to build microwave packages from silicon carbide filled aluminum metal matrix materials. These metal matrix materials offer reduced coefficient of thermal expansion (8 - 12 ppm/° C). However, due to carbide particle impregnation, the machining is not possible by conventional tools and techniques. Also, the question of the seam sealing ring is not resolved. In fact, use of exotic seam sealing techniques like laser and electron beam welding are inappropriate due to blow outs and uneven welding resulting from the beam striking carbide particles.
Electronic packages are usually produced from monolithic metals and alloys. The materials chosen are such that they offer reasonable compromise of thermal dissipation expansion match with ceramics, strength, reduced weight and glass sealability. In packages requiring high power dissipation or large size, these compromises are unacceptable. Such packages are then produced by choosing different metals and alloys as different components of the package and brazing them together to produce a configuration well suited to specific needs. Such packages, however suffer from poor integrity and high cost. Integrity is affected by long term unreliability of brazed joints which compromise the hermetic seal of the packages.
In order to improve package performance, the materials industry has been developing metal matrix materials. These materials are metals having non- metallic particles homogeneously dispersed through them, creating unique characteristics in the material. These particles can be graphite or ceramic, such as silicon carbide, baron, nitride, etc. which are impregnated within copper and aluminum or other alloys. The particles can be in fiber or particulate form. The principle behind the metal matrix materials is that the non-metals or ceramics, which generally have lower coefficient of thermal expansion and in some cases higher thermal conductivity, restrict the expansion of the parent metal or alloy. The amount of non-metal or ceramic loading determines the final characteristics of the product and hence can be tailored to a specific need. The disadvantage, however, is that these materials are not solderable, brazeable or weldable. Resistance welding will not obtain a good joint due to high thermal conductivity of the composite. Laser welding causes dissociation of non-metal or ceramic particulate when the laser beam strikes it. This dissociation results in formation of gases which are entrapped within the weld resulting in loss of hermeticity and unreliable joint.
In the current art of building electronic packages, copper or aluminum alloys are machined to produce a package consisting of a base, side walls and holes drilled in the side walls for installing feed-troughs. The feed-throughs consist of a Kovar lead, with glass sealed to the inner diameter of a Kovar or nickel-iron alloy ring. The glass sealing in the feed-throughs electrically separates the leads from the body, as well as insuring a hermetic seal. The packages are typically plated with silver or gold with a nickel underlayer. The electroplating serves the purpose of providing solderability/brazeability to the packages along with offering corrosion protection. These machined and electroplated packages are then installed with feed- throughs by using gold-tin or gold-germanium braze alloys to braze the inside of the plated hole and outside of the Kovar or nickel-iron ring of the feed- through. An electroplated seal ring consisting of Kovar or stainless steel is also brazed to provide seam sealing capability for the cover at the same time the feed-throughs are brazed. Brazing of Kovar or the stainless steel seam sealing ring presents a problem due to voids and leaching of electroplated material at the brazing temperature, often resulting in leaky packages.
The package now is ready to accept a circuit carrying ceramic card. In some cases, the ceramic cards are soldered or attached by epoxy onto a carrier plate of intermediate expansion prior to epoxying/soldering the carrier plate inside the package. The carrier plate minimizes the effect of expansion mismatch between the package and the ceramic card and tends to prevent the warping or cracking of the ceramic card and in some cases the detachment of ceramic card from the base of the package. This is because copper and aluminum and its alloys have a high coefficient of thermal expansion (aluminum § 22 ppm/° C. and copper § 16 ppm/° C.) compared to the ceramic card at 7 ppm/° C). The disadvantages of carrier plates is in additional weight and barrier to thermal dissipation.
Disclosure of the Invention
In accordance with one form of the present invention a microwave package having controlled heat expansion characteristics is provided. This package includes a block of aluminum or aluminum alloy having a base on one side and being relieved on the opposite side to form a receptacle with a bottom and open top having a peripheral edge. A first layer of material having a low coefficient of thermal expansion in comparison to the block is explosively bonding to the base of the block. A second layer of material having a low coefficient of thermal expansion in comparison to the block extends across the top and is explosively bonded to the peripheral edge. Feed-through openings which communicate with the receptacle can be provided either through the side wall of the block or through the second layer. A cover made of the same material as the second layer extends across and is welded to the second layer. A ceramic substrate is attached to the bottom of the receptacle. The first and second layers can be made of Kovar and/or Invar. A wire extends through each of the feed-through openings and glass can surround each of the wires and hermetically seal the wires around the respective openings. If desired a first interliner can be provided between the first layer and the base of the block and a second interliner can be provided between the second layer and the peripheral edge of the block which can be made of any one of pure aluminum, titanium, tantalum and silver.
The microwave package described above can be made by explosively bonding a layer of material to opposite side of a block of aluminum or aluminum alloy, each of the layers being of a material having a low coefficient of thermal expansion in comparison to the block. Machining can then be done through one of the layers so that material is removed from the block to form a receptacle therein. Lead holes can be provided in the side of the block or one of the layers, the ceramic substrate can be attached to the bottom of the receptacle and feed wires can be extended through the lead holes. A cover can be placed over the layer at the opening and made of the same material as the layer and hermetically sealed thereto, as by welding. The block can be in the form of an elongated bar and a plurality of receptacles can be machined into the bar simultaneously or sequentially whereupon the bar can be cut between the receptacles to form separate microwave packages.
In accordance with a second form of the invention, a hybrid microcircuit package and the* method of making it, comprising a body and side walls of a material having a high coefficient of thermal conductivity, such as a copper bodied device. The package also includes a seal ring, or superimposed frame, mounted on the top edge surface of the side wall structure to permit the attachment thereto of a lid or cover by traditional resistance welding techniques without overheating and softening the body material. The seal ring, or welding ring, is attached to the side wall of the package by the process of explosive clading which is done prior to the body material being machined into the package configuration. In accordance with another form of the present invention, an electronic package having metal matrix material with controlled coefficient of thermal expansion and superior thermal dissipation characteristic is provided. This package includes a block of metal matrix material having a base on one side and being relieved on the opposite side to form a receptacle with a bottom and top having a peripheral edge. A layer of material having the required resistance or laser weldable features in comparison to the block is explosively bonded to the top peripheral edge of the block. Feed-through openings which communicate with the receptacle can be provided through the side wall of the block. A ceramic card carrying electronic components and circuit traces is attached to the bottom of the receptacle. A cover made of the same -14-
or other preferred materials as the top explosively bonded layer can be welded to the peripheral edge of the top layer. This completes the fabrication and sealing of an electronic package. The block can be in the form
05 of an elongated bar with a plate of explosively bonded homogeneous metal explosively bonded to the top surface and a plurality of receptacles can be machined into a bar through the plate simultaneously or sequentially. Thereafter, the receptacles can be cut apart to form
10 separate electronic packages.
The advantages of this invention are readily apparent. In the first forms of the invention, a microwave package can be provided which has the heat conductivity of copper or aluminum but a reduced 5 coefficient of thermal expansion due to the clading of materials to opposite sides of the microwave package which have very low coefficients of thermal expansion. This minimizes the assembly and expansion problems previously described. In another form of the invention,
20 an electronic package is provided which has the properties of metal matrix materials but the weldability or joinability of conventional materials.
Additional advantageous of this invention will become apparent from the description which follows,
25 taken in conjunction with the accompanying drawings.
Brief Description of the Drawings
Figure 1 is a diagrammatic perspective view showing layers of material being explosively clad to a bar of aluminum or aluminum alloy; 30 Figure 2 is perspective view of the composite bar formed in Figure 1;
Figure 3 is an enlarged perspective view of the bar after it has been milled to form a series of receptacles; -15-
Figure 4 is a perspective view of one of the receptacles cut from the bar of Figure 3;
Figure 5 is a perspective view similar to Figure 4, but showing the feed-through openings in the side wall of the receptacle;
Figure 6 is an enlarged perspective view, similar to Figure 5, but showing ceramic substrates in place and the feed-through wires extending through and hermetically sealed within the feed-through openings; Figure 7 is a horizontal section, taken along line 7-7 of Figure 6, showing further detail of the package;
Figure 8 is a perspective view of the microwave package showing the lid in place;
Figure 9 is a fragmentary perspective view showing an alternative embodiment wherein the feed-through openings are in the layer of clad material;
Figure 10 is a perspective view of a composite bar for manufacturing a matrix electronic package;
Figure 11 is a perspective view of one receptacle cut from the composite bar of Figure 10;
Figure 12 is an enlarged perspective view, similar to Figure 11, but showing the ceramic substrates in place and the feed-through wires extending through and hermetically sealed within the feed-through openings; Figure 13 is a horizontal section, taken along line 13-13 of Figure 12, showing further details of the package; and
Figure 14 is a perspective view of the microwave package showing the lid in place.
Best Mode For Carrying Out The Invention
In accordance with one form of this invention, a microwave package can be made which includes a body of aluminum clad with thin layers of Kovar or Invar or other material having a low coefficient of thermal expansion. The average expansion of the package is a function of the volume of the individual materials which form the completed microwave package. Aluminum is a good material to use because of its low weight and good thermal dispassion. However, its coefficient of thermal expansion is quite high, i.e., 22 ppm/° C. On the other hand, Kovar, a well-known commercial alloy consisting of iron-nickel-cobalt or Invar, alloy of iron-nickel, has a low coefficient of thermal expansion. For example, stainless steel has a coefficient of 12 ppm/° C. ; Kovar has a coefficient of thermal expansion of 7 ppm/° C. and Invar has a coefficient of thermal expansion of less than 1 ppm/° C. However, these materials are quite heavy and the latter two do not readily dissipate heat. As best seen Figures 1 and 2, a bar 10 of aluminum can be clad on opposite sides with a bottom layer 12 and an upper layer 14, which may be Kovar or Invar. These layers can vary in thickness, but a thickness of between 40 and 50 mils has been found to be satisfactory. These layers may be clad to the aluminum bar by explosive bonding under techniques well-known in the explosive bonding art. Explosives in the form of chemical powder are placed equally on both the sides of the assembly and detonated. The momentum imparted on each outside material layer produces a metallurgical bond which is also hermetic in nature. In some situations where some aluminum alloys, due to precipitates inside them, are difficult to hermetically attach, the use of easily bondable interliner like pure aluminum, titanium, tantalum or silver is commonly used. In this situation, a five layer composite is assembled and explosively attached.
As seen in Figure 3, the composite bar can be milled through top layer 14 so as to form a plurality of receptacles 16 so that upper layer 14 now forms a rim around the upper edge of each receptacle. The machining is performed such a way that a thin layer of aluminum is left in tact under the cavity of the package. The bottom layer of Kovar or Invar, as shown in Figure 3, remain unmachined and primarily adds to the overall strength of the package and restricts the expansion of aluminum. The machined package is now ready for conventional electroplating and feed-through brazing/soldering. The composite construction in Figure 3 can be cut between each receptacle to form separate microwave packages as shown in Figure 4. Each package has a flange 18 extending from opposite sides thereof. Holes 20 can be drilled in each corner, as shown, for attachment of the microwave base within a piece of equipment. Conveniently, the receptacle 16 has a bottom or base 22, side walls 24 and end walls 26.
Next, feed-through openings 28 are drilled through side walls 24, as shown. Conveniently, feed-through wires 30 extend through each opening 28. The wires 30 can be sealed within feed-through openings 28 by means of a glass or ceramic seal 32. Substrates, such as substrates 34 and 36 can be attached to the aluminum floor 22 of receptacle 16, as by adhesive in the form of an epoxy. The ceramic substrate has a coefficient of thermal expansion of 7 ppm/° C. , about the same as layers 12 and 14. Although the substrates are connected to the aluminum base 22, the expansion of the base will be greatly limited by the adjacent clad layer 12.
These substrates contain circuit boards which are connected to wires 30, as by connectors 38. After all of the electrical connections are made between wires 30 and substrates 34 and 36, a cover 40 can be welded in place around layer 14. Conveniently, cover 40 will be made of the same material as layer 14, i.e., Kovar or Invar which can be welded and hermetically sealed quite easily, as compared to aluminum.
An alternative embodiment is shown in Figure 9 wherein the aluminum layer 10' is thinner than aluminum 10 of the previous embodiment and top layer 14' is thicker, such as on the order of 200 to 250 mils. This provides sufficient space for feed-through openings 28-" to be placed in the layer 14' rather than through the aluminum layer. With this arrangement there is less expansion of openings 28' due to thermal expansion of layer 14' than there would be with aluminum layer 10-". This makes it easier to be sure that a hermetic seal is maintained between the wires 30 and the openings 28'.
A further form of the invention is a process for a product having a copper base and side walls upon which is superimposed a welding ring of Kovar, although it is understood that the invention is not limited to those materials. Other combinations of materials may be used, depending on the package specification, such as molybdenum or copper-tungsten as a body material and
Kovar as a ring material. The structure for this form of the invention is substantially identical to that shown in Figures 4-8 except that receptacle 16 is copper or copper alloy rather than aluminum and bottom layer 12 is omitted.
In accordance with another form of this invention, a metal matrix bar 42 has a top layer 44, such as copper or aluminum, explosively clad thereto. Bar 40 can be composed of a base metal which could be copper or aluminum which has graphite or ceramic particles, such as silicon, carbide, boron or nitride which are homogeneously mixed through the base metal. These particles alter the characteristics of the base metal, such as a lower coefficient of thermal expansion or increasing thermal conductivity. Also, the strength of the material can be increased. The desired characteristics can be increased by adding more of the non-metallic particles or decreased by decreasing the amount of non-metallic particles. By way of example a receptacle has been constructed using 40 - 50% fill silicon carbide impregnated aluminum 6061 matrix with a layer of stainless steel bonded thereto with an inner liner of aluminum alloy between the matrix and the stainless steel layer. Portions of the bar can be milled out simultaneously or sequentially through top layer 44 to form receptacles which can be separated, as described in the previous embodiments so as to form individual receptacles, such as receptacle 46, shown in Figure 11. Conveniently, the receptacle 46 has a bottom or base 48, side walls 50 and end walls 52. Holes 54 can be drilled in each corner of flanges 56, as shown, for attachment of the electronic package base within a piece of equipment. As best seen in Figure 12, feed-through openings 58 are drilled through side walls 50. Advantageously, feed-through wires 60 extend through each opening 58. Wires 60 can be sealed within feed-through openings 58 by means of a glass or ceramic seal 62. Substrates, such as substrates 64 and 66 can be attached to the matrix floor 48 of receptacle 46, as by an epoxy adhesive.
These substrates contain circuit boards which are connected to wires 60, as by connectors 68. After all of the electrical connections are made between wires 60 and substrates 64 and 66, a cover 70 can be welded in place around layer 44. Conveniently, cover 70 will be made of the same material as layer 14, i.e., aluminum or copper which can be welded and hermetically sealed quite easily. -20-
From the foregoing, the advantages of this invention are readily apparent. In one form of the invention, microwave package has been made which is of simple construction yet because it is made of aluminum
05 clad with a material having a lower coefficient of thermal expansion, the microwave package can be made in larger sizes than heretofore possible without exceeding the expansion capabilities of the ceramic substrates placed within them. Furthermore, the clad material is
10 easier to weld than the aluminum. In other words, the advantages of both materials are maintained. The aluminum provides great thermal conductivity but the clad material limits the expansion of the aluminum material, while providing a suitable material for
15 welding a cover in place so as to improve the possibility of a good hermetic seal.
In another form of the invention, a copper body is used, having a layer of Kovar clad thereto.
In a further alternative form of the invention, a
20 metal matrix material can be used which has a layer of copper or aluminum clad to the top surface. The microwave package is formed by milling away a portion of this top surface to form the container. A top cover is provided which is of the same material as the clad layer
25 which facilitates easy welding or attachment thereto. This invention has been described in detail with reference to particular embodiments thereof, but it will be understood that various other modifications can be effected within the spirit and scope of this invention.

Claims

ClaimsIn the Claims:
1. A method of manufacturing a microcircuit housing, comprising the steps of: explosively cladding first and second dissimilar metals to create a solid block of material having the first metal as one surface thereof and the second metal as an opposing surface thereof; creating a cavity in the block which opens through the first metal and into the second metal wherein the first metal is converted to comprise a ring surmounted on the perimeter of the cavity produced in the second metal; mounting electrically conductive leads through the block; inserting semiconductor components into the cavity and attaching the leads thereto; and sealing a cover onto the ring.
2. The method of Claim 1, wherein: the sealing of the cover is done by electrical resistance welding.
3. The method of Claim 1, wherein: the sealing of the cover is done by laser welding.
4. A method of manufacturing a microcircuit housing, comprising the steps of: explosively cladding first and second dissimilar metals to create a solid block of material having the first metal as one surface thereof and the second metal as an opposing surface thereof; creating a cavity in the said block which opens through the first metal to just expose the second metal as a bottom surface of the cavity and wherein the first metal defines the side walls of the cavity; mounting electrically conductive leads through the side walls; inserting semiconductor components into the cavity and interconnecting the leads thereto; and sealing a cover onto the top surfaces of the side walls.
5. The method of Claim 4, where the step of sealing the cover includes: welding of the cover to the upstanding side walls.
6. The method of Claim 4, where the step of sealing the cover includes: laser welding the cover to the upstanding side walls.
7. A high power hybrid microcircuit package comprising: a first material base member having a bottom and upstanding side walls defining an interior volume; ring means of a second material surmounted on said side walls and bonded thereto explosively; and a cover member welded to said ring.
8. The package of Claim 7, wherein: said first material is a metallurgically hard, elastic high thermally conductive metal.
9. The package of Claim 8, wherein: said second material is a low thermal -23-
conductivity, high electrically resistive weldable material.
10. The method of manufacturing a housing into which microcircuit components may be placed, including: explosively bonding first and second dissimilar metals to produce a base member; and machining the base member to produce a flat bottom portion with upstanding side walls defining an interior volume in the first metal and defining a second metal ring surmounted on the side walls.
11. A high power hybrid microcircuit package comprising in combination: a base member having a bottom and upstanding side walls together defining an interior volume, said base member being a metallurgically hard, elastic, high thermally conductive metal; welding ring means disposed contiguously to the top surface of the side walls and explosively clad thereto, said ring means being a low thermal conductivity weldable metal; a plurality of conductor leads penetrating said side walls; semiconductor components disposed within the interior volume of said base member and attached to said bottom of said base member; means electrically connecting said components to said conductor leads; and cover means fabricated from the same characteristic material as said ring means and heat bonded to the ring means.
12. A microwave package having controlled heat expansion characteristics, said package comprising: -24-
a block of aluminum or aluminum alloy having a base on one side and being relieved on the opposite side 05 to form a receptacle with a bottom and an open top having a peripheral edge; a first layer of material having a low coefficient of thermal expansion in comparison to said block explosively bonded to said base of said block; 10 a second layer of material having a low coefficient of thermal expansion in comparison to said block extending across said top and explosively bonded to said peripheral edge; feed-through openings communicating with said 15 receptacle; and a cover made of the same material as said second layer extending across and welded to said second layer.
13. Apparatus, as claimed in Claim 12, further including: a ceramic substrate attached to said bottom of said receptacle.
14. Apparatus, as claimed in Claim 12, wherein: said first and second layer and said cover are
Kovar or Invar.
15. Apparatus, as claimed in Claim 12, further including:
A wire extending through each feed-through opening; and 05 glass surrounding each said wire and hermetically sealing it around the respective openings.
16. Apparatus, as claimed in Claim 12 wherein: said first and second layer and said cover have a coefficient of thermal expansion which does not exceed 7 ppm/°. C.
17. Apparatus, as claimed in Claim 12, further including: a first interliner between said first layer and said base of said block; and a second interliner between said second layer and said peripheral edge of said block, said first and second interliners being any one of pure aluminum, titanium, tantalum and silver.
18. Apparatus, as claimed in Claim 12, wherein: said feed-through openings are in an aluminum side wall formed in said block.
19. Apparatus, as claimed in Claim 12, wherein: said feed-through openings are in said second layer.
20. A method of manufacturing a hermetically sealed microwave package having controlled expansion characteristics, said method comprising: explosively bonding a layer of material to opposite sides of a block of aluminum or aluminum alloy, each of said layers being of a material having a low coefficient of thermal expansion in comparison to said block; machining through one of said layers and removing material from said block to form a receptacle therein; forming lead openings in said one of said layers; attaching a ceramic substrate to the bottom of said receptacle; -26-
extending feed-through wire through said lead openings and connecting them to said substrate; placing a cover over said one of said layers which is made of the same material as said one of said 20 layers; and hermetically sealing said cover to said one of said layers.
21. A method as claimed in Claim 20, wherein: said block is an elongated bar; a plurality of receptacles are machined in said bar; and 05 said bar is cut between said receptacles to form separate packages.
22. A matrix electronic package having controlled heat expansion characteristics, said package comprising: a block of metal matrix material having a base on one side and being relieved on the opposite side to 05 form a receptacle with a bottom and an open top having a peripheral edge; a layer of weldable material extending across said top and explosively bonded to said peripheral edge; feed-through openings communicating with said 10 receptacle; and a cover made of the same material as said layer extending across and sealed to said second layer by welding.
23. Apparatus, as claimed in Claim 22, further including: a ceramic substrate attached to said bottom of said receptacle.
24. Apparatus, as claimed in Claim 23, wherein: said layer and said cover are copper or aluminum.
25. Apparatus, as claimed in Claim 22, further including: a wire extending through each feed-through opening; and glass surrounding each said wire and hermetically sealing it around the respective openings.
26. Apparatus, as claimed in Claim 22, wherein: said matrix material is metal having non-metal particles homogeneously disbursed therethrough.
27. Apparatus, as claimed in Claim 26, wherein: said metal is copper or aluminum; and said particles are ceramic.
28. Apparatus, as claimed in Claim 22, wherein: said feed-through openings are in the matrix material side wall formed in said block.
29. Apparatus, as claimed in Claim 22, wherein: said feed-through openings are in said second layer.
30. A method of manufacturing a hermetically sealed matrix electronic package having controlled expansion characteristics, said method comprising: explosively bonding a layer of material to a side of a block of aluminum or copper, said layer being of a weldable material; machining through said layer and removing material from said block to form a receptacle therein having side walls; forming lead openings in one of said side walls; attaching a ceramic substrate to the bottom of said receptacle; extending feed-through wire through said lead openings and connecting them to said substrate; placing a cover over said layer which is made of the same material as said layer; and hermetically sealing said cover to said layer.
31. A method as claimed in Claim 30, wherein: said block is an elongated bar; a plurality of receptacles are machined in said bar; and said bar is cut between said receptacles to form separate packages.
PCT/US1990/001006 1989-03-02 1990-02-22 Explosively formed electronic packages and method of manufacture WO1990010308A1 (en)

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
US07/318,157 US5022144A (en) 1989-03-02 1989-03-02 Method of manufacture power hybrid microcircuit
US318,157 1989-03-02
US33884989A 1989-04-17 1989-04-17
US338,849 1989-04-17
US360,068 1989-06-01
US07/360,068 US5001299A (en) 1989-04-17 1989-06-01 Explosively formed electronic packages

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WO1990010308A1 true WO1990010308A1 (en) 1990-09-07

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WO1996013059A2 (en) * 1994-10-17 1996-05-02 Litton Systems, Inc. Hermetically sealed microwave integrated circuit package with ground plane fused to package frame
WO1996013059A3 (en) * 1994-10-17 1996-06-27 Litton Systems Inc Hermetically sealed microwave integrated circuit package with ground plane fused to package frame

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