About the 1996 TMS Annual Meeting: Monday Morning Sessions (February 5)

COMPOSITES FOR HIGH PERFORMANCE ELECTRONIC PACKAGING AND THERMAL MANAGEMENT APPLICATIONS

Program Organizers: Subhash Katri, Materials Resources, Inc., 1162 Horshoe Drive, Blue Bell, PA 19422

Monday, AM Room: Grand H

February 5, 1996 Location: Anaheim Marriott Hotel

Session Chairperson: Michael J. Koczak, Drexel University, Philadelphia, PA 19104

8:30 am

DESIGN AND FABRICATION OF COOLED GR/CU STRUCTURES: Daniel L. Vrable, Fred L. Beavers, SPARTA, Inc., 9455 Towne Centre Dr., San Diego, CA 92121-1964

This presentation summarizes and discusses some of SPARTA's efforts in the design, development and fabrication of Gr/Cu structures for highly loaded thermal/structural applications. The applications include; leading edges and engine components for the National Aerospace Plane, radiators for space power, flexible high conductance thermal straps for space power and electronic SEM- E modules. The components for these applications have common design requirements of managing the transfer of high heat fluxes or minimizing component weight, tailoring the coefficient of thermal expansion to minimize thermal strains, and enhancing other structural attributes such as stiffness or strength. Discussed is the methodology that is used in developing the Gr/Cu composite components. This methodology includes; the composite design, thermal/structural analysis, materials characterization and property determination, composite part producibility, proto- type development and testing, and full scale component fabrication and test. Several examples are provided to explain and help illustrate the successful insertion of advanced Gr/Cu composite materials into high technology components. The discussion addresses the selection of the fiber type, fiber architecture, fiber volume fraction, enhancement of the short transverse thermal conductivity and various processing methods.

8:55 am

COPPER/GRAPHITE BASED METAL MATRIX COMPOSITES FOR IMPROVED THERMAL MANAGEMENT OF ELECTRONIC DEVICES: Joseph K. Weeks, Jared L. Sommer, Technical Research Associates, Inc., 2257 S. 1100 E. Salt Lake City, UT 84106

As electronic components continue to shrink while they increase in capability, the need to remove waste heat is becoming significantly more difficult. TRA has developed a series of copper/graphite products with better properties than can be obtained in conventional materials. High conductivity graphite fibers are incorporated in a pure copper matrix through a simple fiber coating and casting process. The resulting composites offer significant improvements in thermal conductivity, lower weight, and lower thermal expansion than alternative materials. Since molten copper wets the coated fiber surface, superior bonding between the fibers and the copper is produced. The efforts to produce economical composite materials through the utilization of lower cost graphite fibers will be discussed. Properties of the composites will be presented. New products and applications only made possible by the fiber coating will be discussed.

9:20 am

METAL MATRIX COMPOSITE RADIATOR PANELS FOR SPACECRAFT THERMAL MANAGEMENT: Uday Kashalikar, Foster-Miller Inc., 350 Second Ave., Waltam, MA 02154

During this research program, Foster- Miller demonstrated an innovative, effective and potentially low cost metal matrix composite (MMC) radiator panel for spacecraft thermal management. The component used ultrahigh thermal conductivity graphite fiber in an aluminum 6063 matrix. The light weight was achieved by using corrugated radiator panel design that provides flexural stiffness equivalent to a conventional "sandwich" panel without the weight penalty of a honeycomb core. Additionally, a housing for the heat pipe was cast in place, thereby eliminating the high cost joining step. An MMC radiator component was fabricated to net shape via pressure casting. The P 120 graphite fiber reinforced Al- 6063 component showed a 16 to 30 percent lower thermal impedance than the baseline aluminum sandwich component. Use of the Kl100 graphite fiber is expected to produce over 50 percent reduction in the radiator thermal impedance along with substantial reduction in panel weight.

9:55 am

IMPROVED THROUGH-THICKNESS THERMAL CONDUCTIVITY IN ADVANCED POLYMER COMPOSITES: Thomas G. Campbell, Composites Technology Division, Foster-Miller, Inc., 350 Second Ave., Waltham, MA 02154

Advanced composite materials are used extensively in aircraft but have had limited use in areas of thermal applications. Inplane conductivities can be greatly enhanced by using pitch based carbon fibers. However, most areas of heat transfer require heat flow through the thickness of the laminate. This property is controlled by the epoxy which has low conductivity. A special application of the Z- Fiber process has been developed that permits introduction of up to 10% of the surface area of high conductivity pitch fibers in the through- thickness direction. This enables carbon epoxy laminates to generate heat transfer capabilities approaching aluminum. A 3- D laminate is constructed from 2D materials generating improved properties without the loss of inplane properties generally found in 3D materials. The progress to date will be presented, including test data verifying the through-thickness conductivities of greater than 8 W/mK, compared to the l W/mK found in standard laminates, at minimal loss of inplane strength.

10:20 am BREAK

10:35 am

CERMETS FOR MICROELECTRONICS PACKAGING: M.K. Premkumar, Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069

The availability of suitable new materials for packaging is critical to the continuing advancement of microelectronics technology. As circuit densities and switching speeds continue to increase, and electronic devices are used in more hostile environments, there is an increasing need for packaging materials with superior properties. Traditional packaging materials such as Kovar that have been successfully used for decades are no longer capable of meeting the thermal and reliability requirements of the new designs. New classes of ceramics and composite materials are being developed to meet these challenges and Al- SiC cermet is one such material system. These cermets are composites with near optimum combinations of thermal expansion coefficient, thermal conductivity, density and elastic modulus. This paper describes the attributes of this material system as well as Alcoa's manufacturing technology for production of cermet microelectronics packaging products. The unique capabilities of this technology will be illustrated via application examples.

11:00 am

CAST SILICON CARBIDE REINFORCED ALUMINUM MATRIX COMPOSITE FOR REMOTE POWER CONTROLLER (RPC) PACKAGES: Suraj Rawal, Tom Green, Bruce Lanning, Bruce Benson, Martin Marietta Technologies, Inc., R & T, Mechanical, P. O. Box 179, MS F 3085, Denver, CO

Cast silicon carbide particulate reinforced aluminum matrix composites (SiCp/Al) provide desired properties and characteristics for lightweight remote power controller packages. These composites with high volume percent (2 55 v/o) particulates offer excellent combination of low density, high strength, high conductivity, properties to provide performance improvements and weight savings compared to baseline kovar and copper/tungsten packages. Using pressure assist infiltration process, both the baseplates and integrated electronic enclosures (i.e. baseplate with sidewalls) were successfully cast. In addition, a few SiCp/Al baseplates were also cast by high pressure infiltration process. Each of these components were electroplated with nickel/copper and gold. The plated baseplates were used to assemble electronic enclosures by soldering copper or kovar sidewalls. These baseplates and electronic enclosures were extensively evaluated using optical and scanning electron microscopy, thermal- mechanical tests and salt- fog tests, and thermal cycling tests. Subsequently, the beryllia substrate (with electronic components) was bonded to the composite baseplate, and performance tests were conducted to verify that each electronic component remained within the desired operational temperature range. This paper presents the results of materials characterization, and thermal perforrnance tests and discusses the technology issues to be resolved to ensure metal matrix composite technology insertion into RPC packages.

11:25 am

APPLICATIONS FOR ULTRA-HIGH THERMAL CONDUCTIVITY GRAPHITE FIBERS: Thomas F. Fleming,C.D. Levan, Amoco Performance Products Inc., William C. Riley, Research Opportunities Inc.

Thermal management has become a limiting problem for both military and commercial systems. High thermal conductivity graphite fibers provide a breakthrough in the efficiency of conductive cooling. The fibers have exceedingly high specific modulus and a negative coefficient of thermal expansion; these properties can be used to tailor the thermal expansion of composite material to virtually any required level. This paper discusses the nature of fibers, the translation of fiber properties into composites including metal, organic, and carbon matrix. Emphasis is on applications for the resulting high thermal conductivity composites. These applications include electronic packaging, aircraft and spacecraft.

11:50 am

FABRICATION TECHNIQUES FOR ADVANCED CARBON-CARBON COMPOSITE HEAT EXCHANGERS: William H. Altergott, Patricia J. Schwartz Foster-Miller Inc., 350 Second Ave., Walham, MA 02154

This paper describes various innovative brazing techniques that address the thermal expansion mismatch problems associated with the joining of carbon- carbon (C/C) composites to refractory metals and high thermal conductivity metals for advanced heat exchanger applications. Upon cooling from braze temperature, thermal expansion mismatch between the C/C and the metal results in formation of deleterious residual stresses throughout the joint. Residual interlaminar stresses may lead to cracking of brittle refractory metals. Even barring material failure, the residual stresses may compromise the ability of the joint to withstand the mechanical and thermal stresses imposed during the service. Specific brazing innovations discussed in this paper include: lO use of multiple interlayers in the joint where a compliant material accommodates thermal expansion mismatch stresses via plastic flow, while a stiff interlayer reacts shear stresses to off- load the C/C, 2) hybrid braze/diffusion bonding process in which the resulting joint may withstand higher service temperatures than the braze temperatures, and 3) coatings in faying surfaces that prevent formation of brittle and unstable compounds at the braze interface, and promote chemical/thermal stability of the Joint during prolonged exposure to elevated service temperatures. We will describe potential applications for advanced C/C heat exchangers including hypersonic vehicle structures, advanced propulsion systems, spacecraft therlllal management and high density electronics packaging.

12:15 pm

POWDER INJECTION MOLDING OF THERMAL MANAGMENT MATERIALS FOR MICROELECTRONIC APPLICATIONS: R. M. German, 118 Research West, Penn State University, University Park, PA 16802-6809

Thermal management materials create challenges both with material selection and component fabrication. Powder injection molding provides an important fabrication route for near net shaping high quality composite systems with tailored thermal properties. Analysis has identified several candidate materials, including W- Cu, Mo- Cu, and SiC- Al. These have been developed to a demonstration state using actual geometries and tested for thermal properties. W- Cu is the most viable material for heat sink and packaging applications, delivering thermal conductivities in the 230 W/m/deg.C range. But, major opportunities are apparent in systems based on AlN. This presentation outlines the powder injection molding of thermal management structures and isolates processing options and applications for these liquid phase sintered composites. Demonstration heat spreaders, boilers, and microwave packages are used to illustrate the state of technology.