Defects in nickel plating layers on copper-metallized substrates induced by thermal cycles

The reliability of electronic substrates at high temperature is a significant issue for high-power semiconductor modules. To improve the reliability, it is essential to understand and reduce thermal-cycling-induced surface roughening of metal layers on the substrates. We observed the surfaces and cross sections of nickel plating layers on copper-metallized silicon nitride substrates by active metal brazing after the substrates were subjected to thermal cycles of -40 to 250°C. No cracks were observed on the surfaces of the nickel layers on substrates that were subjected to 100 and 200 thermal cycles. However, voids or cavities were observed just under the nickel surfaces on those substrates. We considered that those voids or cavities were formed by thermal stress induced by thermal cycling and that they could be one of the origins of cracks in the nickel layers.