Investigation of Sn Whisker Growth in Electroplated Sn and Sn-Ag as a Function of Plating Variables and Storage Conditions

Sn whiskers are becoming a serious reliability issue in Pb-free electronic packaging applications. Among the numerous Sn whisker mitigation strategies, minor alloying additions to Sn have proven effective. In this study, several commercial Sn and Sn-Ag baths of low-whisker formulations are evaluated to develop optimum mitigation strategies for electroplated surfaces. The effects of plating variables and storage conditions, including plating thickness and current density, on Sn whisker growth are investigated with matte Sn, matte Sn-Ag, and bright Sn-Ag electroplated on a Si substrate. Two different storage conditions are applied: an ambient condition (30°C, dry air) and a high-temperature/high-humidity condition (55°C, 85% relative humidity). Scanning electron microscopy is employed to record the Sn whisker growth history of each sample up to 4,000 h. Transmission electron microscopy, X-ray diffraction, and focused ion beam technique are used to understand the microstructure, the formation of intermetallic compounds, oxidation, the Sn whisker growth mechanism, and other features.