Tin whiskers formation and growth on immersion sn surface finish under external stresses by bending

Abstract

Deposited tin (Sn) layers used as lead-free solderable finish on the semiconductor devices are known to form whiskers. These whiskers are a single crystal of tin that spontaneously grows from the surface of tin within weeks to years. Thus, they can cause shorts and the failure of a whole electronic circuit. In this research, the effect of external stresses applied by bending on the tin whiskers formation and growth was investigated on immersion Sn surface finish. The plating time was 10 minutes to produce 1.4 μm coating thickness on the copper substrate and exposed for 1, 4, and 8 weeks under the environment of 30°C/60% RH for bent and non-bent samples. It was found that the non-bent Sn surface had uniform ts distributed on the entire surface. Unlike the non-bent Sn surface, the surface of bent samples had non-uniform tin whiskers distribution. The tin whiskers formed more and grew longer at the lower stress region of the bent surface as compared to the higher stress region, based on the micrograph observed using the field emission scanning electron microscopy (FESEM).