Highly oriented graphite(HOG)is expected as a heat sink of the next generation power semiconductors. In the case of graphite, due to poor solder wettability, a metallic bonding layer must be formed on the graphite for the heat sink. Furthermore, the HOG is easily oxidized and broken by thermal spraying. Copper coatings was form by low-temperature plasma spraying(LTPS)method as a newly developed thermal spray process which can form a coating at a relatively low temperature and low particle velocity. Two types of graphite substrates with different thermal conductivities were prepared, and the influence of the thermal conductivity properties for the coating formability was examined. Furthermore, the effect of substrate surface roughness for the coating formability was also investigated. From the results of evaluation, it is possible to form a Cu coating on the lowly oriented graphite(LOG)substrate with a relatively low thermal conductivity by the LTPS method. No film was formed on the HOG smooth substrate with extremely high thermal conductivity. However, the high roughness HOG substrate could be formed the coating as well as the high roughness LOG substrate. The roughening of the graphite material improves the coating forming efficiency.

View full abstract