Generation and growth of whiskers and nodules from electroplated tin and tin lead films on copper or nickel substrate were studied by scanning electron microscopy and X ray diffraction. In the case of copper substrate, whiskers generated in 0.3 Ms on the electroplated tin film whose thickness was 1 mm. On the other hand, electroplated tin lead film on copper substrate showed only nodules even after 13 Ms. Residual stress of electroplated tin film (1 mm) and the number of whiskers increased with the amount of copper tin intermetallic compounds (Cu 6 Sn 5 ) which developed between the plated film and the substrate of copper. Although residual stress and the amount of Cu 6 Sn 5 also increased in the tin lead system, the morphology of the layer of Cu 6 Sn 5 was more uniform compared with the case of tin electroplated film on copper substrate. When the electroplated tin lead film was subjected to the compression testing by a ball of zirconium oxide (1 mm diameter, 2.94 N 0.605 Ms), the edge of the indentation did not show any whiskers but diffusion of lead was observed from right under the zirconium oxide ball to the fringe, as well as Ostwald growth of lead. In the case of electroplated tin film on nickel substrate, whose residual stress was weakly tensional, nickel tin intermetallic compounds (Ni 3 Sn, Ni 3 Sn 2 , Ni 3 Sn 4 ) uniformly developed immediately after electroplating, and no whiskers were observed even after the compression testing. While growth of whiskers is considered to be due to diffusion of tin atoms induced by inhomogeneous strain field in the electroplated film, lead atoms in tin lead system is considered to diffuse rapidly toward the free surface to release residual stress and to generate many nodules.

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 (Cu 6 Sn 5 ) 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.

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