The effects of the electroless copper coating to the thermal expansion behaviors of silicon carbide particles reinforced copper matrix composites for the electronic packaging applications

Abstract

The demands for advanced thermal management materials with high thermal conductivity and low coefficient of thermal expansion (CTE) are expected to increase due to the technological progress in the thermal management hardware. Silicon carbide reinforced copper matrix (Cu-SiCp) composites are highly rated as thermal management materials due to the high thermal conductivity and low CTE properties. But the Cu-SiCp composites fabricated via the conventional powder metallurgy methods have inferior thermophysical properties due to the absence of bonding between the copper matrix and the SiCp reinforcement. In order to improve the bonding between the two constituents, the SiCp were copper coated via electroless coating process. The electroless plating process consisted of surface cleaning, sensitization, activation and copper deposition processes. In between the processes, the ceramic particles were rinsed thoroughly with deionized water to minimize contamination. Based on the experimental results and findings, a continuous copper deposition on the SiCp was obtained via the electroless plating process. The copper film was found to be high in purity and homogeneously deposited on the SiCp surfaces. The thickness of the coated copper layer was roughly estimated to be less than 1mm. The copper coated layer on the SiCp also improved the bonding between the copper matrix and SiCp reinforcement. The copper coated layer improved the green strength of the composites thus allowed a high volume fraction of SiCp to be incorporated into the copper matrix. The CTE values of the copper coated Cu-SiCp composites were significantly lower than those of the uncoated Cu-SiCp composites. The CTE of the coated Cu-SiCp composites were in agreement with Kernel’s model. The microstructure examination of the composites also supports the CTE results. A good bonding between the copper matrix and the SiCp reinforcement exists in the copper coated Cu-SiCp composites. Where else in the non-coated Cu-SiCp composites, submicron gaps were observed between the copper matrix and the SiCp reinforcement. This could be the reasons behind the higher CTE values as compared to copper coated Cu-SiCp composites.