Whisker test methods of JEITA whisker growth mechanism for test methods

As the industry moves toward lead-free electronics, a replacement for the traditional tin-lead plating is required. Pure tin is the coating of choice for many suppliers, but there is a well-known problem with the growth of tin whiskers. A whisker is comprised of a tin crystal which, after an incubation period, grows with time. Whiskers may grow long enough to cause shorts in electronic circuits. A test method is required for evaluating the reliability risk inherent in tin whiskers. The Japanese government requested the Japan Electronics and Information Technology Industries Association (JEITA) to establish test methods for solderability, reliability, whisker, and migration for lead-free electronics. The goal of this subcommittee was to propose the test methods for tin whiskers by March 2004. The committee carried out a literature survey, and developed hypotheses for whisker growth, which was then applied to test methods. Two types of studies were undertaken. One is a fundamental study to verify the hypothesis. The other looked at accelerated tests to develop recommended test conditions. As a result, we found that the diffusion of copper, oxidation, and thermal cycling all influence tin whisker growth. This paper describes the results of the fundamental studies and reports on the JEITA whisker growth mechanism.