Fort Collins, Colorado 80525, USA
M. Sun and M. Pecht
CALCE Electronic Products and Systems Center
University of Maryland, College Park, MD 20742
The electrically conductive contact area essentially determines the resistance of electrical contacts over the lifetime of a contact pair. Due to surface roughness, contact between two surfaces occurs at points where the asperities on the mating surfaces physically touch. Away from these asperities, the surfaces do not touch. Assuming that the asperity points are not covered with insulating films, the area of the asperity points in contact defines the electrical contact area. However, over the lifetime of an electronic system, the electrical contact area can be diminished by numerous failure mechanisms such as corrosion. Insulating corrosion films can grow from defect sites in the noble metal plated contact surface, spread over the surface of the noble metal and seep gradually into the asperity points, thereby decreasing the electrically conductive area in contact.
Previously published studies on electrical contact physics [1-10] have experimentally demonstrated that corrosion film formation is controlled by diffusion either in the surface film or in the near-surface region. However, no correlation has been established between the lifetime resistance of electrical contacts and the growth kinetics of corrosion film on the surfaces of noble metal plated electrical contacts. None of aforementioned studies have also established a comprehensive model that includes such parameters as contact force, electrical voltage drop across the contact area, and temperature over system lifetime for either bare metal or noble metal plated electrical contacts.
The purpose of this paper is to discuss the effects of key parameters including mechanical contact force, electrical voltage drop across the constriction, and environmental temperature on the lifetime contact resistance of noble metal plated electrical contacts in terms of the thermodynamics and kinetics of contact materials. The kinetic approach here is then used to predict the lifetime resistance in a static noble metal plated electrical contact pair.
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