Property of Tin Oxide Film Formed on Tin-Plated Connector Contacts

A tin (Sn)-plated surface Is usually covered with tin oxide film such as SnO. The tin oxide film influences greatly contact resistance characteristics. Therefore, it is important to study contact resistance characteristics under low contact load. In this study, a growth law of the oxide film (relationship between film thickness and exposure time) was found for exposure temperature range from 25°C to 150°C. The growth law at 150°C is different from at other lower temperature. Next, formations of the film and crystal state were clarified by XPS analysis. The surface state and contact traces for elevated temperature were examined by AFM, and growth of an inter metallic compound layer between a copper substrate and plated tin layer was discussed. Moreover, the relationship between contact resistance and film thickness due to elevated temperature were clarified. For high temperature such as 150°C, peculiar relationships between contact resistance and film thickness were found, and these relationships strongly depend on growth of the inter metallic compound. Change of the surface state was examined by AMF images and observation of contact traces.