Deformation of Crystal Morphology in Tin Plated Contact Layer caused by Loading

概要

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Tin (Sn) plated contacts are widely used Surfaces of plated tin are covered with their oxide film, but it is possible to obtain low contact resistance by applying high contact load. Tendency in down size of the connector will be increased in the near future. Therefore, it is important to study contacts resistance characteristics under low contact load. In this study, relationships between contact resistance and change of contact traces of the tin plated specimen were examined. In the contact configuration for hemisphere of platinum and tin plated flat contact, the hemisphere surface sank into the softer tin plated flat surface. In the results, piling up of crystal grain at periphery of the contact trace occurs. During this process, sudden decrease in contact resistance was found. To clarify the phenomena, morphology changes of contact traces were observed by AFM, SEM and EBSD. And also mechanical stress distribution in the tin-plated layer was analyzed by FEM. Formation of the crystal of the contact area is forced to outside of the contact area. Due to the peculiar distribution of the stress, the crystal grains are separated and push out the contact area. This phenomenon is very different from commonly observed decrease in contact resistance due to elastic and plastic deformation.
2011-11-10