Contact resistance behavior of nanocrystalline copper and palladium films under fretting conditions

The effect of fretting on the contact resistance behavior of nanocrystalline Cu and Pd films deposited on Cu, Ni, and Al plates in contact with Cu, Al and Sn-plated copper wire conductors was investigated. The tests were conducted with a simulated connector configuration using a differential thermal expansion fixture to produce a fretting motion of 30 /spl mu/m at a frequency of 0.005 Hz. In addition to the contact resistance measurements, scanning electron microscopy (SEM) and X-ray fluorescence (EDX) analyses were used to study the processes involved. The results show that in practically all cases, the nanocrystalline Cu and Pd films had a beneficial effect on the contact resistance behavior as manifested by relatively small fluctuations of the contact resistance with fretting time. However, when the films were worn out by the fretting action, a rapid increase in the contact resistance was observed. SEM and EDX analyses of the worn contact zones revealed that these were damaged by fretting action and in some cases transfer of material was observed. However, this damage was considerably less pronounced than that observed when the base metals were subjected to the same fretting conditions. It is believed that the beneficial effect of nanocrystalline films is due to the improved mechanical properties of these films.