Due to the recent increase in electronic devices mounted on automobiles, a large number of connectors, especially low-cost tin plated connectors are being used. As a result, their contact reliability has become problematic. Furthermore, for the connectors which are subjected to fretting wear caused by heat cycle and vibrations, the contact resistance increases because of wear of tin and deposition of oxides, which generates problems of poor contact. This study is intended to analyze the change in contact resistance of tin plated connectors from the start of fretting wear to the end of their lifetime from the viewpoint of practical reliability, and to observe the trace and the characteristics of fretting wear microscopically. This study found that wear and oxidation of tin plated connectors start immediately with fretting wear, and thus accumulation of abrasion powder on fretting areas causes connectors to reach to the end of their useful lifetime quickly. Especially, it was demonstrated that amplitude of fretting has a considerable influence on a connector's lifetime. It is made clear that air-tightness, so-called "gas-tight" of tin in a fretting area influences fretting wear considerably.

In recent years, there has been increasing demand to miniaturize wiring harness connectors in automobiles due to the increasing volume of electronic equipment and the reduction of the installation space allocated for the electronic equipment in automobiles for the comfort of the passengers. With this demand, contact failure caused by the fretting corrosion is expected to become a serious problem. In this report, we examined micro-structural observations of fretting contacts of two different tin plating thicknesses using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) and so on. Based on the results, we compared the microstructure difference of fretting contact caused by the difference of the tin plating thickness.

Constriction resistance is calculated by numerical analysis using Laplace's equations for electric potential of steady state in many cases of contact spot dispersion-status. The results show that contact resistance does not increase beyond 1.5 times even if the total real contact area is about 15% of the apparent contact area. When real contact area is at least about 60% of the apparent contact area, the contact resistance is approximately the same as the constriction resistance acquired from the apparent contact area. When the real contact area is about 50% of the apparent contact area, the contact resistance is approximately constant without regard to the contact shape and contact-point dispersion layout. Therefore, it is proved that contact resistance can be practically calculated using apparent contact area instead of real contact area when there are many contact points caused by metal to metal contact.