Formation of Cu Nanodots on Diamond Surface to Improve Heat Transfer in Cu/D Composites

Abstract

Diamond-dispersed copper matrix (Cu/D) composite materials with different interfacial configurations are fabricated through powder metallurgy and their thermal performances are evaluated. An innovative solution to chemically bond copper (Cu) to diamond (D) has been investigated and compared to the traditional Cu/D bonding process involving carbide-forming additives such as boron (B) or chromium (Cr). The proposed solution consists of coating diamond reinforcements with Cu particles through a gas-solid nucleation and growth process. The Cu particle-coating acts as a chemical bonding agent at the Cu-D interface during hot pressing, leading to cohesive and thermally conductive Cu/D composites with no carbide-forming additives. Investigation of the microstructure of the Cu/D materials through scanning electron microscopy, transmission electron microscopy, and atomic force microscopy analyses is coupled with thermal performance evaluations through thermal diffusivity, dilatometry, and thermal cycling. Cu/D composites fabricated with 40 vol% of Cu-coated diamonds exhibit a thermal conductivity of 475 W m À1 K À1 and a thermal expansion coefficient of 12 Â 10 À6 C À1 . These promising thermal performances are superior to that of B-carbide-bonded Cu/D composites and similar to that of Cr-carbidebonded Cu/D composites fabricated in this study. Moreover, the Cu/D composites fabricated with Cu-coated diamonds exhibit higher thermal cycling resistance than carbide-bonded materials, which are affected by the brittleness of the carbide interphase upon repeated heating and cooling cycles. The as-developed materials can be applicable as heat spreaders for thermal management of power electronic packages. The copper-carbon chemical bonding solution proposed in this article may also be found interesting to other areas of electronic packaging, such as brazing solders, direct bonded copper substrates, and polymer coatings.