An analysis of relationship between contact resistance and fracture of oxide film for connector contacts using finite element method

In automotive connectors, electrical current through the tin-plating flows as a result of fracture of the oxide film due to the expansion on the terminal surface area by contact load, and following metal to metal contact. It has been believed that the fracture can easily occur under mechanical contact of two mating terminals, since the oxide film on the tin-plated surface is only several nm thick. However, the whole process, from the fracture of oxide film, metal to metal contact, to the following decrease of contact resistance, has not been visualized by electrical and mechanical simulation. In the present paper, a method to analyze the oxide film fracture and following decrease of contact resistance was developed by using finite element method, to clarify the process of the fracture. It was found by using a single fine projection contact model, that the fracture of the oxide film took place where deformation of tin-plating was concentrated, since the oxide film was subject to tension by the plastic deformation of tin-plating. The change in the contact resistance after the oxide film fracture was also observed by current-flow analysis. Finally, the sudden decrease of the contact resistance observed at the certain contact load in experiment was successfully explained by the combination of single fine projection and multipoint contact models.