Contact fretting of electronic connectors

Connector contact resistance may become unstable if fretting occurs. Such m otions result in the formation of insulating oxides on the surface of base metal contacts or organic polymers on contacts made of platinum group metal s. These degradations ale termed fretting corrosion and frictional polymeri zation, respectively. Motion may be caused by external vibration or fluctua ting temperature. The lower the frequency of movement, the fewer the number of cycles to contact failure. Increasing the contact normal load or reduci ng the amplitude of movement may stabilize the connection. Tin and palladiu m and many of their alloys are especially prone to fretting failure. Tin ma ted to gold is worse than ail-tin contacts. Gold and high gold-silver alloy s that are softer when mated to palladium stabilize contact resistance sinc e these metals transfer to the palladium during fretting; but flash gold co atings on palladium and palladium nickel offer marginal improvement for the gold often quickly wears out. Dissimilar metal contact pairs show behavior s like that of the metal which predominates on the surface by transfer. Con tact lubricants can often prevent fretting failures and may even restore un lubricated failed contacts to satisfactory service.