At the surface of the tin-plated brass substrate placed at 50°C, the tin whiskers grew evidently within a short time, due to the formation of zinc oxide on the surface and alloying between plated tin and brass substrate as supposed. While at the surface of the brass substrate plated with tin on nickel, there was no trace of the tin whisker at all. Nickel greatly represses the diffusion of base metal materials into the tin layer. Nickel and tin plated monolithic chip capacitors placed at the same condition for 18 years were also observed and the tin whisker growth phenomenon has never taken place either. As a result, the tin plated film on the nickel over silver thick film does not provide the tin whisker growth. Nickel underplating plays an important role in tin plated capacitors for not only the solder leaching but also the tin whisker growth problems.