Effects of Plating Baths for Cu-undercoat on Thermal Peeling of Tin Plated Phosphor-bronze

To clarify the mechanism of thermally accelerated adhesion-loss of plated films of tin on phosphor-bronze and to find methods for providing protection from this phenomenon, the effects of the plating conditions of copper undercoat were examined with plating baths of copper cyanide, copper pyrophosphate, copper sulfate and copper fluoborate. Main findings are summarized as follows. 1. Tin-coated phosphor-bronze is very insensitive to thermal peeling when copper undercoat is electroplated from copper cyanide baths, and very sensitive when the undercoat is electroplated from copper pyrophosphate baths. 2. In electroplated tin-copper systems, no effect of copper electroplating bath on diffusivity was observed. It is suggested that the susceptibility of thermal peeling of tin-coated phosphor-bronze to plating conditions of copper undercoat is due not to any acceleration of diffusion by the undercoat but to the interaction of vacancies induced in the undercoat by diffusion with the matrix.