Temperature dependence of microstructure and hardness of vacuum plasma sprayed Cu-Mo composite coatings

A copper baseplate has been commonly adopted as a heat spreader material for power modules. However, the coefficient of thermal expansion (CTE) mismatch between copper and Si has always been a troublesome problem and the primary disadvantage of using a copper baseplate because the interface between the substrate and the heat spreader is one of the main failure sources of a power module. To solve this problem, the tailoring of a Cu-Mo composite material with high thermal conductivity and suitable thermal expansion coefficients was suggested by thermal spray process which makes it possible to easily fabricate components of functionally graded materials (FGMs) and allows the multiple steps of powder production, molding, degassing and consolidation to be reduced into a single processing step. By utilizing the vacuum plasma spraying technique, dense and well-distributed Cu-Mo metal matrix composite coatings without oxides and amorphous phase were obtained. Vertically grown intralamellar columnar structure, which is promising for increasing the heat transfer, was also observed in plasma sprayed Cu-Mo metal matrix composite coatings. Microhardness of Cu-Mo composite coatings follows a rule of mixture based on the volume fraction and fits nicely to a linear relation regardless of different measured temperatures.