Corrosion properties of tin-copper alloy coatings in aspect of tin whisker growth

The appearance of corrosion at elevated temperature and humidity conditions could also be responsible for the growth of tin whiskers. In this paper the relation between the corrosion of different tin-copper alloys (0-5 wt.% Cu) and whisker growth was investigated. The alloys, applied as surface coating on copper base, were stored at an elevated temperature and humidity condition (85 °C/85% RH). It was observed that the tin-copper alloys show differences in the tendencies of the whisker growth. Polarisation measurements were performed to find a relation between whiskering behaviour and corrosion resistance of the alloys. The corrosion behaviour of the layers was also studied by cross-sectioning with a focused ion beam. The series of tests have shown that the whisker appearance probability of different alloys is affected by three different factors: corrosion resistance of the surface finishing, expansion rate of the corrosion product and recrystallization speed of the metal/alloy.