Material coupon test method to simulate contact performance under automotive conditions

There has been a great upsurge in research and failure analysis on automotive interconnections over the past 10 years. Failures are often attributed to a combination of loss of normal force, fretting corrosion, general corrosion, overheating, plating degradation, and others. Much of the research effort has been to establish a reproducible link between material system and electrical performance reliability. Metal alloy producers and material platers have attempted to contribute to this effort by performing specific coupon studies which characterize the electrical performance of their products. Generally, these coupon studies do not address the critical differences between the performance of a flat coupon sample and a formed connector. Within the automotive industry, there are various performance tests applied to interconnection components which evaluate electrical performance results after simulated or accelerated service conditions. This paper describes the development of a test method which is capable of simulating the key performance characteristics of an automotive interconnection. Recommendations for future improvements are included. The goal of this development was to provide a testing system which evaluates the degradation of contact resistance in samples which closely represent formed components, without the encumbrance of complete component fabrication. The following criteria were selected as minimum test system requirements : Samples must be easily fabricated from the material systems of interest; The environment must provide for thermal cycling (Delta T=125/spl deg/C, min.); Provide for stress relaxation of a formed contact spring to manifest in the performance result; Provide for the motion required for fretting corrosion at the contact surface; The change in contact resistance with time must be measured at intervals close enough to identify critical phenomena; Samples must be easily retrieved and prepared for contact surface analysis after cycle testing is completed. Initial results comparing heavy hot tin coatings on both brass and copper beryllium show an extremely high difference in the rate of increase in contact resistance.