The Impact of Electro-Migration on Various Contact Materials

An analytical model of circular contact spots was used in conjunction with numerical methods to estimate the impact electro-migration has on separable power contacts. A single spot model was developed using relative variables to estimate the rate of degradation. The single spot model was generalized to include variations in spot size and change in contact voltage and subsequently used to conduct an analysis of the performance of multi-spot contact interfaces. It was shown how contact material properties were incorporated into the simulations which provided a basis to compare the performances of various materials. The results indicate that materials such as aluminum and tin exhibit potential susceptibility to electro-migration degradation. This depends on what type of diffusion dominates the aging process. It was found that grain boundary (pipe) diffusion causes this process to speed up while lattice diffusion is generally too slow to cause problems. Consequently, it is recommended that testing of vulnerable materials at currents above the application requirements is recommended to establish where the threshold for electro-migration occurs.