Investigation of tin whisker growth: The effects of Ni and Ag underplates

A major problem with tin electroplating is the formation of tin whiskers. These are spontaneous protrusions of few microns in diameter and up to hundreds of microns or even millimeters in length. There are several mitigation strategies and using a nickel or silver underplate is proven to be excellent in preventing the forming of Cu₆Sn₅ intermetallics. Still there are not many scientific researches about the effects of this mitigation strategy. Therefore we have tested leadframe samples in different temperature and humidity conditions (105degC/100% relative humidity (RH), 50degC/25% RH) for over 3400 hours. Both leadframes were on bronze substrates and had 1-2 mum underplates (silver or nickel) with 5-7 mum tin on the top. Our results have shown hillock and whisker growth differences on the samples depending on the nature of the different environmental circumstances, which is originated to the different stress-causing mechanisms, and also growth differences have been found on the different underplate materials.