Tin Whiskers

Pure tin is currently the most widely employed lead-free finish for plating of component terminals despite its propensity to spontaneous whisker formation. Whiskers are filamentary crystals, conductive and mechanically strong, measuring up to a few millimetres, though the common variety observed on matt tin finish on copper substrate was hardly ever reported to exceed 0.5 mm. A positive stress gradient within the Sn layer, that is either a lowering compressive or an increasing tensile stress towards the root of a whisker, is reputed as the driving force for whisker formation. The formation of whisker is a major reliability concern for the electronic industry. Whisker related failures in electric and electronic hardware have been reported since the 1940 and the failure risk cannot be overlooked especially in modern electronic systems. Understanding the tin whisker phenomenon and further developing mitigation strategies and test methods for evaluating whisker performance are all important tasks to be fulfilled in the future.