Fabrication and thermal properties of hot press sintered Cr-coated carbon fiber/Cu composites

The mesophase pitch-based short carbon fibers (CF_s) with ultra-high thermal conductivity and negative coefficient of thermal expansion (CTE) were compounded with Cu via hot press sintering. In order to improve the bonding state between CF_s and Cu, Cr was pre-coated on CF_s by chemical vapor deposition technique. The microstructure and thermal properties of the Cr-coated CF_s/Cu composites were studied. The results show that most of Cr coating reacts with C forming to a thin, continuous and uniform Cr₇C₃ interfacial layer, and small amount of them diffuses into Cu matrix during the preparation process, which causes the interface structure between CF_s and Cu to change from week mechanical bonding into good metallurgical bonding. Consequently, the thermal properties of the composites are improved effectively. The Cr-coated CF_s/Cu composites with 40vol%-55vol% CF_s achieve the relative densities higher than 97.5%, the in-plane thermal conductivities to 393-419 W(mK)^-1 and the in-plane CTE ranging of 5.1×10^-6-8.4×10^-6 K^-1. The composites are promising materials for electronic packaging applications due to their high thermal conductivities, low CTE and good machinabilities.