Discontinuous growth of tin whiskers

Three types of discontinuous growth behaviour of tin whiskers are described. First, growth bands were observed in whiskers on a tin finish held in an ambient environment for 30 days after plating; the spacing between the growth bands was 0.2–0.4?µm. Second, growth of a whisker was discontinuous with time, in which there was about 30 days of stagnation, after which whisker growth reoccurred. Third, an irregular whisker with a triangular morphology and abruptly changing cross-section was observed by SEM. Discontinuous whisker growth behaviour challenges the previously proposed mechanism of tin whisker growth. It is postulated that alternating breakdown and self-curing in air of an oxide film at point defects could be a reason for discontinuous growth of whiskers.