Effect of normal forces on fretting corrosion of tin-coated electrical contacts.

Electrical connectors have been extensively used as the electrical connecting component in various electronic systems. The performance of the electrical connector directly affects the performance of an entire system. Fretting corrosion is generally recognized as an essential failure mechanism for an electrical contact. Major factors affecting the fretting corrosion include current magnitude, normal contact force, displacement amplitude, relative humidity, frequency, and temperature. In order to investigate the effect of normal forces on fretting corrosion behavior, normal forces were fixed at 1N, 1.25N, 1.5N, 2N, 2.5N for various displacement amplitudes. Riders and flats made of 0.3mm-thick brass sheet were coated with tin. The change of the electrical resistance was measured by applying constant current and displacement amplitudes to the upper sphere contact specimen, fixing the flat specimen. The normal force (F) shows a linear relationship with the threshold displacement amplitude (δth). When the displacement amplitude increases with increasing normal force, the plating layer was severely worn due to contact pressure. Dimples were found on the surfaces of the central part of the specimens showing infinite lifetime, suggesting that a soft metal-to-metal contact formed just before separation of the mated specimens at the end of the test. Specimens with an infinite lifetime tested under partial slip condition showed a relatively low oxygen concentration on the center of the wear surface. It is very important to design an electrical connector contact to maintain partial slip by using the information on the normal force and displacement amplitude in order to achieve infinite lifetime.