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

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1 Author(s)
Haque, C.A. ; AT&T Bell Laboratories, Columbus, OH, USA

An electrodeposited copper-tin-zinc alloy having a nominal composition in the range by weight of 55-65 percent Cu, 20-30 percent Sn, and 10-20 percent Zn is commonly used as a surface finish on electronic components, particularly fuse end caps. The contact resistance of brass disks plated with this alloy (1µm thick) is 1-10Omegadue to a film of the oxides of Sn, Zn, and some Cu. Heat treatment at 100°C causes the oxide thickness to increase, with the contact resistance simultaneously increasing to > 100Omega. 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 x 10-17cm2/s. The oxide film is very brittle and readily fractures due to tangential wipe, when contact resistance would fall to the millohm range from > 100Omega. 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.

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Components, Hybrids, and Manufacturing Technology, IEEE Transactions on  (Volume:8 ,  Issue: 1 )