Peculiarities Characteristics Between Contact Trace and Contact Resistance of Tin Plated Contacts

Tin (Sn) plated contacts are widely used by acceptable properties of low cost and stability of contact resistance under high contact load as substitution of gold (Au) plated contacts. In the present time, these type contacts are applied to automotives. 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 increase 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 were examined by the tin plated specimen. It was found that in the contact configuration for hemisphere of platinum and tin plated flat contact, the hemisphere surface sank into the softer tin plated flat surface with increase in contact load. In the results, piling up of the periphery of the contact trace occurs. Moreover, it was found that crystal grains piles up at the periphery of the true contact area. During the piling up of the periphery, sudden decrease in contact resistance was found. This phenomenon is very different from usual decrease in contact resistance due to elastic and plastic deformation.