Humidity Effects on Sn Whisker Formation

Due to legislative issues, Pb-containing metallizations on semiconductor components are rapidly converted to Pb-free alternatives. One of the most popular alternatives is Sn electroplating. The major problem of these platings is the formation of Sn whiskers. In earlier publications, two mechanisms were uncovered that are responsible for whisker growth. However, these mechanisms do not explain whisker growth in high humidity. Therefore, Freescale, Infineon, Philips, and STMicrolectronics (E4) joined forces and started a design of experiment (DoE) in order to resolve this mechanism. It is shown that in high humidities, whiskers grow due to oxidation and corrosion of the Sn plating, irrespective of the base material. It is also shown that board assembly mitigates the whisker growth by this mechanism but does not completely prevent it