Tin coating techniques for copper-base alloys - The effects on friction, wear and electric properties

The effect of coating technique of tin on copper-base alloy upon friction, macro-wear and electric properties were studied in a model contact tool. The contact constitutes of a flat stationary sample and a moving hemispherical rider, simulating insertions and withdrawals of a separable connector. Three different tin coating techniques were used; hot dipping, electroplating, and reflowing (electroplating with a subsequent quick fusion and solidification of the tin coating). The wear of the flat sample was divided into three defined stages when evaluating the measurement results; plowing of the rider into the soft tin layer (stage I), sliding of the rider on the hard intermetallic compound (stage II), and, finally, penetration of the intermetallic compound (stage III) with subsequent plowing of the rider into the substrate material. The difference between the stages regarding friction, wear and electric properties were significant. In this paper it is proposed that differences between the tin coating techniques regarding friction, wear and electric properties are mainly correlated to differences in thickness of the pure residual tin layer as well as differences in thickness of the intermetallic compound.