Tin whisker growth on bright Sn films supported by lead-frame alloy substrates

In this work, we fabricate bright tin films on two kinds of representative lead-frame substrates (C194 and FeNi42). Ni film was electroplated between Sn plating and the alloy substrate as a diffusion barrier. The samples were stored under 55 °C / 85% RH condition for up to 8,000 hours. The effect of alloy substrate, tin film thickness and Ni barrier on the tin whisker growth was investigated for a comprehensive understanding of the tin whisker growth behavior. It was found that the substrate type has great influence in the tin whisker density. Further, the density and average length of the tin whisker were related to the film thickness. Ni barrier was found strongly prevent Sn whiskers or hillocks growth even after thermal/ humidity storage for 8,000 hours. Surface and cross-sectional observations of IMC formed at the interface were also carried out using field emission scanning electron microscope (FE-SEM).