Improved hollow cathode magnetron deposition for producing high thermal conductivity graphite_copper composite

Abstract

High thermal conductivity heat sinks for thermal management in electronic packaging is enabling to a variety of advanced electronic applications. State-of-the-art heat sinks have thermal conductivities, K, generally less than 180 W mK−1, and frequently have large expansion mismatch with chips such as silicon and gallium arsenide. A unique technology for producing graphite fiberreinforced copper (Cf/Cu) composite has been developed that produces thermal conductivities up to 454 W mK−1 utilizing a K= 640 W mK−1 fiber reinforcement (with a potential for 800 W mK−1 when utilizing a K=1100 W mK−1 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 (ca. 1100 W mK−1) and acts as a heat spreader.