Current Redistribution across an Aging Contact Interface

In an un-aged contact, the spot to spot variation of current was previously shown to depend on factors such as spot size and the interaction of the currents through each spot. In addition, it was shown as a contact degrades due to high current densities, the distribution of relative current densities across each spot change with time. Moreover, it was seen that the spot to spot current density across the interface varies significantly. These phenomena were shown to cause a cascade failure mode for power contacts. In the latter case, it was assumed that each spot degraded at the same rate according to an assumed mathematical model. Consequently, the latter results were only understood as qualitative. This paper develops a more quantitative single spot model which provides a mathematical aging function based on the changing conductivity across a single spot. Moreover, spot size and voltage change are incorporated into the single spot results. This enabled a more quantitative analysis of current re-distribution during aging of a multi-spot interface. These results demonstrate a more quantitatively based set of characteristics for the cascade failure mechanism. In addition, the changing contact resistance and associated temperature-rise, were shown to exhibit behavior similar to real power contact observations, where increases accelerate as aging progresses.