Electric contact behavior of Cu-Sn intermetallic compound formed in tin platings

An intermetallic compound (IMC) Cu/sub 6/Sn/sub 5/ is formed in tin platings on phosphorous bronze substrates when the coupons are subjected to thermal shocks. The coupons were cross-sectioned to show the growth of Cu-Sn IMC which was identified by X-ray diffraction method. Sliding and fretting electric contact behavior were studied on such surfaces. Previous studies in other laboratories found that the contact resistance in such experiments was quite high. In the present experiments, however, a specially made lubricant was used which dramatically lowered the contact resistance. It was found that the oxide and other contaminant particles normally located in the contact area of the probe were removed by the lubricant. But in agreement with earlier studies, obvious cracks could easily be seen on the surface of the substrate after sliding or fretting experiments. Thus the main beneficial effect of the lubricant in these kinds of experiments was to reduce the contact resistance.