Temperature - Time Effects on Film Growth and Contact Resistance of a Plated Copper-Tin-Zinc Alloy used as a Surface Finish on Electronic Components

摘要

The contact resistance of brass discs plated with this alloy (1μm thick) is 1 to 10Ω due to a film of the oxides of Sn, Zn, and some Cu. Heat treatment in clean air at 100°C causes the oxide thickness to increase, with the contact resistance simultaneously increasing to >100Ω. At 75°C and below, oxide growth is not detectable. The growth rate of the oxide film at 100°C is parabolic with a rate constant of 1.9 × 10~(-17) cm~2/sec. The oxide film is very brittle and readily fractures due to tangential wipe, when Contact Resistance would fall to the milliohm range from >100Ω. This alloy as a surface finish on electronic components has the potential of causing overheating, transients in logic circuits and, adding a significant resistance to the circuit involved particularly in the absence of any wiping action.