Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/045—Alloys based on refractory metals

Definitions

• the present invention relates to metal admixtures and processes for making them. More particularly, the present invention relates to copper-tungsten admixtures having from approximately 5 to 50 weight percent copper made by an injection molding and liquid sintering process.
• the packages must of necessity have electrically insulated leads which extend through the walls of the package.
• the leads must be hermetically sealed and electrically insulated.
• the electronic packages generally are designed to contain heat generating components, so it is highly desirable to have the package constructed of materials which have a high thermal conductivity.
• the packages must be hermetically sealed in order to protect the electrical components which are contained therein. Because these packages travel from sea level to the vacuum of outer space and back in a matter of minutes, any gas leakage is intolerable.
• the materials used to seal the openings through which the electrical leads pass are inelastic and have coefficients of thermal expansion which are substantially different from those of most metallic materials. Thus, thermal cycling causes stress in the seal and contributes to its rapid failure.
• composition of matter comprising a high density copper- tungsten admixture which has a high thermal conductivity and a rate of thermal expansion which can be matched to that of many inelastic insulation-seal materials such as glass and ceramics.
• the high density copper-tungsten admixture is very impervious to gas.
• the copper-tungsten composition is produced according to the present invention by a powder metallurgical process which involves injection molding to form complex shapes and uses a liquid-phase sintering step to densify the part.
• a powder metallurgical process which involves injection molding to form complex shapes and uses a liquid-phase sintering step to densify the part.
• Such molding processes have in general been proposed before see for example, Wiech, U.S. patent Nos. 4,374,457, 4,305,756 and 4,445,956. Reference is invited to these prior Wiech patents for the disclosure of such procedures.
• Powder metallurgical procedures which involve injectio molding and liquid phase sintering have the capability of producing net-shaped parts in very complex configurations t very close tolerances.
• Net-shaped parts are those parts or products which do not require any further machining, shapin or forming beyond the liquid sintering phase to be useful for their intended purposes.
• the tolerances which can be achieved are less than +/- 0.003 inches per inch. Since th product is injection molded, the shapes of the parts can be extremely complex.
• a hermetically sealed elctronic package is defined as having a helium gas leak rate of no greater than
• the copper-tungsten admixture products of this invention generally exhibit leak rates as low as approximately 2 10 -10 cm3 of helium per second.
• the "hermeticity" of electronic packages constructed from this material is substantially in excess of ⁇ that which is required.
• the thermal conductivity of the copper-tungsten admixture according to the present invention is generally better than approximately 0.40 and preferably at least 0.42
• the thermal conductivity is measured for a material which contains about 5 weight percent copper. When less than 5 weight percent copper is present, the benefits of the present invention are generally not fully realized. At 25 weight percent copper, the thermal conductivity is generally more than approximately 0.60 and preferably at least about
• the thermal conductivity is generally more than approximately
• the linear coefficient of thermal expansion is -generally directly proportional to the volume percent of copper in tungsten.
• a value of about 7.0 parts per million/degree centigrade corresponds to 11 weight percent ⁇ copper and 9.4 parts per million/degree centigrade corresponds to about 25 weight percent copper.
• the linear coefficient of thermal expansion of the copper-tungsten material according to the present invention can generally be matched to that of the insulator-seal material in the electronic package by adjusting the percentage of copper in the admixture.
• the thermal performance of the copper-tungsten material products of the present invention particularly when considered in light of the hermeticity and the production of these materials in net-shaped configurations very significantly advances the art.
• the provision of a net- shaped product eliminates many of the previous requirements for machining and assembling electronic packages. Since the assembling of electronic packages according to previous teachings often involved brazing and soldering steps which permitted the opportunity for gas leaks, the elimination of most such steps according to the present invention greatly improves the reliability of electronic packages.
• the use of the present invention makes it possible to increase the power density of the package while maintaining the same or improved reliability.
• the electrical leads which conduct electrical current into and out of the electronic package from the same copper-tungsten material according to the present invention.
• the thermal performance of the leads may thus be matched to that of the case. Since the high density copper-tungsten material is a good electrical conductor, the electrical efficiency of the package is also excellent.
• the copper and the tungsten raw materials for use according to the present invention are provided in very finely divided form and in a highly pure state.
• the particle sizes of the copper material are less than about 20 microns and the average particle size of the tungsten powder is less than about 40 microns. In general, the average particle size for these materials is below about ten microns.
• the amount of surface oxygen on the particles has a substantial impact on the nature of the finished product. At surface oxygen concentrations of more than approximately 5,000 parts per million on the copper, the results are very erratic and unpredictable during the sintering phase. Also, the surface oxygen concentration on the tungsten particles should be less than about 1,500 parts per million. In general, the particles are substantially equiaxed in shape.
• the impurities in the raw materials should be kept to an absolute minimum. As little as 2 percent of nickel, for example, will reduce the thermal conductivity by as much as 30 to 40 percent. As little as 0.3 of one percent of various impurities, such as, for example, oxides and trace amounts of lead and tin, may reduce the thermal conductivity by as much as 15 to 20 percent.
• a high purity copper-tungsten material was prepared with 35 weight percent copper and 65 weight percent tungsten.
• the tunysten powder had an average particle size between 1 and 2 microns, surface oxygen of less than about 1,400 parts per million and other impurities of approximately 300 parts per million.
• Copper powder having an average particle size of between 8 and 10 microns, surface oxygen of less than 800 parts per million, determined by hydrogen weight loss, and other impurities less than 500 parts per million was used. Both the tungsten and copper powder particles were substantially equiaxed.
• a binder consisting of 39.47 weight percent polypropylene, 9.74 weight percent carnuba wax, 48.73 weight percent paraffin wax and 2.06 weight percent stearic acid was prepared.
• the binder was admixed in the proportion of 4.3 weight percent with the above copper-tungsten powders.
• the admixing was accomplished under a vacuum so as to encourage the binder to wet the particulate surface and eliminate entrapped air, thus reducing the porosity and improving the thermal properties of the final product.
• the resulting admixture of binder and metal powders was injection molded to produce a product having the desired shape.
• the product, called a yreen part was heated in air to a temperature of about 207 degrees centigrade for a period of two days to remove the wax.
• the resultant intermediate product was then heated in an atmosphere containing 25 percent by volume hydrogen and 75 percent by volume of nitrogen at temperatures up to about 800 degrees centigrade until the polypropylene was removed.
• the temperature was then raised to about 1,235 degrees centigrade and held there for about three hours in an atmosphere containing 75 percent by volume hydrogen and 25 percent by volume nitrogen.
• the resultant sintered net- shaped product was allowed to cool for approximately six hours to room temperature.
• the physical properties of interest were determined to be as follows:
• the copper content was reduced to 15 weight percent and the tungsten increased to 85 weight percent.
• the same type of powders described in the first example were again used.
• the mixing, injection molding, and debinding procedures were again the same.
• the sintering temperature was increased to 1 ,450 degree centigrade.
• the physical properties of interest were determined.
• the linear thermal coefficient of expansion was 7.56 parts per million per degree centigrade and the density was 15.3 grams per cubic centimeter. The density is 94 percent of full theoretical density.
• a high purity copper-tungsten material was prepared which had 25 weight percent copper and 75 weight percent tungsten.
• the tungsten powder which was utilized had an average particle size of between 1 and 2 microns, surface oxygen of less than about 1,400 parts per million and other impurities of approximately 300 parts per million.
• a binder consisting of 39.47 weight percent polypropylene, 9.74 weight percent carnuba wax, 48.73 weight percent paraffin was and 2.06 weight percent stearic acid was prepared.
• the tungsten and copper powders were proportioned so that 25 weight percent copper and 75 weight percent tungsten were utilized.
• the metallic powder was admixed with the binder in proportions such that 4.3 weight percent of the resulting admixture was binder material.
• the admixing was accomplished under a vacuum so as to encourage the binder to wet the particulate surface and eliminate entrained air, thus reducing the porosity and improving the thermal properties of the final product.
• the resulting admixture of binder and metal powders was injection molded to produce a product having the desired shape.
• the product called a green part, was heated in air to a temperature of about 207 degrees centigrade for a period of two days to remove the wax.
• the resultant intermediate product was then heated in an atmosphere containing 25 percent by volume hydrogen and 75 percent by volume of nitrogen at temperatures up to about 500 degrees centigrade until the polypropylene was removed.
• the temperature was then raised to about 1235 degrees centigrade and held there for approximately three hours.
• the resultant sintered net- shaped product was allowed to cool for approximately six hours.
• the thermal conductivity was determined to be 0.496

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Powder Metallurgy (AREA)
• Cooling Or The Like Of Semiconductors Or Solid State Devices (AREA)

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Citations (2)

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• 1988
  • 1988-09-21 DE DE88908854T patent/DE3881030T2/de not_active Expired - Fee Related
  • 1988-09-21 KR KR1019890700936A patent/KR960013889B1/ko active IP Right Grant
  • 1988-09-21 AU AU25318/88A patent/AU615964B2/en not_active Ceased
  • 1988-09-21 EP EP88908854A patent/EP0336944B1/de not_active Expired - Lifetime
  • 1988-09-21 WO PCT/US1988/003253 patent/WO1989002803A1/en active IP Right Grant
  • 1988-09-21 JP JP63508103A patent/JP2811454B2/ja not_active Expired - Lifetime
  • 1988-09-27 CA CA000578597A patent/CA1302739C/en not_active Expired - Fee Related
  • 1988-09-27 IL IL87859A patent/IL87859A/xx unknown
• 1989
  • 1989-05-26 FI FI892568A patent/FI86604C/fi not_active IP Right Cessation

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