Current-induced aging of contact spots

Recent experimental work on aluminium contact interfaces carrying direct current suggests that the electric current itself can be responsible for degradation of the contact spots. Scanning electron microscopy studies of the metallurgy inside the minute conducting areas support this conclusion. The high current densities and the high temperature in the contact zones cause a mass transport by electromigration. This mass flow through the interface is a nonstationary process, leading to an accumulation of vacancies cluster and form voids and cavities, and the electrical conductivity is gradually reduced. Eventually, the contact spot is so heavily degraded that it is unable to pass the high current densities, and new current paths are created in the vicinity of the original spot. This can be considered as an intrinsic aging mechanism. In contrast to all other degradation processes, the current itself, i.e. the flow of electrons, is found to impair the electrical properties of the contact spot directly