The impact of sliding motion and current load on the deterioration of tin-coated contact terminals

The deterioration of tin-coated connectors is mainly caused by macro wear during insertion/withdrawal and fretting during operation. The focal point of this macro-wear study is the increase in the contact resistance when the pure-tin layer is removed and the rider slides on the hard and uneven intermetallic compound, which is referred to as Stage II. Stage II has been divided into two "sub-stages", referred to as Stage IIa and Stage IIb, with the transition point between the two defined by a sharp rise in the magnitude of the voltage drop. The transition between Stages Ila and IIb ranged between 70-130 mV, independent of current load. The upper and lower ends of this range correspond to the softening and melting voltage of tin respectively. The sliding speed has a significant effect on the deterioration during Stage IIa, while the current load does not significantly influence the deterioration as long as the electrically-induced heat is low. In this study an outline of an oxidation model is proposed for describing the deterioration during Stage IIa, and to determine an oxidation constant. Furthermore, the length of duration of Stage IIa can be derived and expressed simply as the inverted value of the oxidation constant.