Growth behaviors of tin whiskers on Sn-Al coating

Spontaneous growth of tin whiskers have been a threat in electronic devices for several decades. The growth behaviors of tin whiskers on a Sn-Al coating was investigated in this paper. A polycrystalline 100 μm thick Sn coating was fabricated on a Al substrate by reflow soldering. The coating was confirmed as a hypereutectic Sn-Al coating. The microstructure of Sn-Al coating consisted of primary α-Al phases and Sn-Al eutectic phases. Tin whiskers was found showing a fast growth rate on the Sn-Al coating. The grains of the Sn-Al coating showed random orientations which was different from the coating fabricated by electroplate. Tin whiskers preferred to grow on the Sn grain with (001) plane in Z direction. Grain boundaries were not found at the whisker root indicating that lattice diffusion should be response for the growth of the whisker.