Effect of strongly oxidizing environment on whisker growth form tin coating

The effect of a strongly oxidizing environment (105 °C/100%RH) on tin whisker formation has been studied with Ni and Ag underlayered samples between the tin surface coating and the bronze base material of the electronic components leads. Using nickel or silver underlayer between the copper substrate and the tin coating can be useful for preventing whiskers. The underlayer blocks the formation of Cu6Sn5 intermetallics which is one of the root causes of whisker growth. The silver underlayered samples started extreme whiskering after 2200 h; on the Ni underlayered samples only hillocks have been observed. The shape of the whiskers did not resemble to the usually known whisker appearance. The oxidizing environment creates tin-oxide fast and causes thick layers of SnOx to appear on the surface of the samples and also on the whiskers. This caused the periodic appearance of large amounts of whiskers; but it blocks the length of them. This combined effect results in only large amounts of short whiskers and even causing the thickness of the tin layer to shrink by 80%. The series of tests has also showed that the nickel underlayered samples resisted whiskering better than the silver underlayered samples.