Materials, environment, motion, and electrical contact failure mechanisms

Surface films produced by natural aging mechanisms are primarily responsible for the failure of electrical contacts in the field. Some of the mechanisms of organic and inorganic film formation are reviewed. It is demonstrated that the sudden failure mode is entirely consistent with contemporary theories of film effects and asperity models of the contact interface. Reliability of the electrical contact is shown to be a function of materials, the operating environment, and interface motion. On the basis of the present understanding of film formation kinetics and typical asperity sizes, it is concluded that interfaces do not degrade by a simple asperity erosion process. However, film formation occurs in areas surrounding asperity peaks due to environmental ingress. It is proposed that this source of film, together with microscopic movement of the interface, can account for a major portion of the intermittent and hard contact failures related to surface films. These results strongly indicate that the disturbance/motion effects must be incorporated into laboratory qualification procedures. If they are not, typical results may grossly underestimate probable contact performance