Microstructural Characteristics of Oxide Layer Growth on Tin Whisker and Finish Surface

The growth of oxide film on both Sn whisker and finish surfaces was observed using TEM and their crystal structures were analyzed using EELS. Only uniformly formed SnO2 structure of rutile phase was observed on the surface of Sn. In the samples stored at room temperature for 20 years, the thickness of oxide layer on finish surface (17 nm with polycrystalline structure) was thicker than that on whisker surface (6.5 nm with amorphous structure). The tin oxide growth tendency exhibited a parabolic curve with a gentle slope. However, at samples stored at 55 °C for 16 months, oxide layers consisted of 1 nm amorphous and 9 nm polycrystalline SnO2 were observed on whisker surfaces. The amorphous structure of SnO2 layer (5.5 nm) was also formed on the finish surfaces. No difference was found in the measured resistance of the Sn finish surface when the surface was etched by Ga+ ions.