Detection of a-Spots in Aluminum Contacts

ln contacts between aluminum conductors the current densities in the a-spots may become very high. When the contact carries heavy direct current, this results in material transport from one contact member to the other by electromigration. By using a tracer metal this can be utilized to map the a-spots on the contact surfaces after separation, using X-ray microanalysis or electron microscopy. The results from an experimental study of a-spots in aluminum contacts are presented. The experimental arrangements and conditions are described, and some typical results selected from 30 contacts are shown. It appears that the mass transfer is caused not only by atom migration, but that an important contribution is made by the asymmetric fracture occurring when the contact members are separated. Results that confirm the relationship between the constriction resistance and the a-spot configuration are presented.