High Thermal Conductivity Graphite Copper Composites with Diamond Coatings for Thermal Management Packaging Applications
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MER Corporation, Metal Matrix Composites, 7960 S. Kolb Road, Tucson, AZ 85715 ABSTRACT
High thermal conductivity heat sinks for thermal management in electronic packaging is enabling to a variety of advanced electronic applications. Heat sinks in industrial semiconductor application have thermal conductivities generally less than 180 W/mK, and frequently have large expansion mismatch with chips such as silicon and gallium arsenide. A unique technology of producing graphite fiber reinforced copper (Cf/Cu) composite has been developed that produced thermal conductivities up to 454 W/mK utilizing a K=640 W/mK fiber reinforcement (with a potential for 800 W/mK when utilizing a K = 1100 W/mK P130 fiber) and thermal expansion that can be matched to chip materials. The process consists of utilizing a hollow cathode sputtering process to deposit a bonding layer followed by copper on spread graphite fibers, which are then consolidated into composites with architectures to achieve desired thermal conductivity and thermal expansion. The copper thickness determines graphite fiber loading up to 80 %. In heat sink applications, where the electrical conductivity of the graphite fiber reinforced copper composite is a problem, processing has been developed for applying electrically insulating diamond film, which has high thermal conductivity and acts as a heat spreader. INTRODUCTION
Thermal management is one of the key critical aspects in the design of multichip modules to ensure reliability at increased packing and power densities in electronic devices. This issue becomes especially important for the successful implementation of three-dimensional integrated circuit architectures that are currently being developed. A novel type of metal matrix composite (MMC) heat sink material consisting of high thermal conductivity graphite fiber reinforced copper matrix composite has a significantly higher thermal conductivity than conventional heat sink packaging materials. To comply with the specific requirements of the semiconductor component environment, the composite material to be used as a substrate and/or packaging has to provide compatible coefficient of thermal expansion (CTE), mechanical strength (including interlaminar strength), and electrical compatibility. Such materials can also be utilized for other (non-semiconductor) thermal management applications such as fusion reactor components, energy storage and conversion, and functionally gradient materials (FGMs) that incorporate a thermal management function. High-volume processing capability of such a material will also be of importance for industrial applications. EXPERIMENT
The emphasis of this investigation was on producing high thermal conductivity metal matrix composites that would comply with the requirement profile of a semiconductor substrate or 147
Mat. Res. Soc. Symp. Proc. Vol. 390 0 1995 Materials Research Society
packaging material. Most of the related issues were addressed in the selection of a high-thermal conductivity graphite fiber (AMOCO P120, K=640 W/mK) and
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