Alternatively, it may suggest that the electrochemical oxide
influences the rate at the whiskers grow once the whisker has penetrated the
oxide layer. It might be expected that when a whisker penetrates through the
oxide film, the whisker would have a similar rate of growth to the untreated samples;
therefore, the electrochemical oxide also appears to be having an influence on
the driving force for whisker growth as well as inhibiting whisker initiation.
It was shown previously that for Sn-Cu on Cu, IMC growth didn’t appear to be
influenced by the presence of the electrochemical oxide [1]. In the absence of an oxide film, the surface
of the tin serves as a source for vacancies to facilitate tin diffusion through
the coating, to support the growth of whiskers [2]. However, the presence of a sufficiently thick
oxide may impede diffusion of tin atoms by reducing the number of available
surface vacancies [3], therefore slowing the rate at which whiskers may
grow. This may suggest that whisker growth on the electrochemically oxidised
samples is diffusion limited.