Making Electrical Contact to Layered Surfaces

In many cases the metallic surface of a contact member consists of layers of conducting materials. Typically, one might find a combination of base metals plated with barrier layers such as nickel with a top coating of Gold, Tin or Palladium. These materials may have significantly different conductivities that impact the overall contact resistance of individual contact spots. In the present paper, the impact of under layers on resistance is considered using basic electromagnetic theory. Specifically, the approach used is the capacitance method as described in Holm's book on electrical contacts. These results are obtained by modifying the capacitance to include the effects of layer thickness and conductivity and show the impact on contact resistance. It is believed this approach provides accurate as well as additional capability over other methods such as provided by Williamson and Greenwood as discussed in this work.