Effect of Fretting on the Contact Resistance of Palladium

Abstract

The fretting of palladium contacts was studied at conditions relevant to their use in separable electronic connectors. Wrought, clad, and electroplated palladium mated to wrought palladium develop high contact resistance due to the formation of friction polymer. This can occur in ordinary room air which contains traces of organic air pollutants. Contact resistance changes diminish as force is increased. Static contact resistance measurements were made in small steps along wear tracks during fretting tests. It was found that the contact resistance increases were greatest at or near the ends due to the accumulation of polymer, and that the numbers of fretting cycles required to produce high contact resistance diminish sharply as track length is increased from 10 to 160 #m. Thin coatings of a polyphenyl ether contact lubricant significantly improve the stability of contact resistance, and contacts flooded with this fluid showed little degradation. This is attributable to its ability to disperse the polymer which is formed. Likewise, palladium contacts immersed in toluene, a polymer precursor commonly used in laboratory studies of friction polymerization, display stable contact resistance. These findings are compared to those of previous studies of the contact resistance of palladium during fretting, and it is shown that differences in interpretation of results are due to variations in the apparatus which were used.