Effect of Lead Co-Deposition on the Whisker Growth on Electrodeposited tin Film

Abstract

This study investigated the effect of Pb co-deposition on the whisker growth on electrodeposited tin film onto phosphor bronze substrate by using XRD, FE-SEM, FE-EPMA and GD-OES. FE-SEM observation revealed that the whisker growth was suppressed with the increase in the amount of Pb in deposits and the increase in the thickness of Sn deposit. The diffusion layer consisting of intermetallic compounds (Cu6Sn5) was formed at the interface between the Sn deposits and substrate as Cu diffused from the substrate to the Sn deposits. This diffusion layer grew, and the compressive stresses in Sn deposits increased correspondingly. On the other hand, diffusion layer and compressive stresses in Sn-10 mass% Pb alloy deposits were smaller than these in Sn deposits. The depression efficiency of the whisker growth by Pb co-deposition is attributed to the depression of the diffusion layer and the reduction of the compressive stresses.