Risk and Mitigation for Tin Whiskers and Tin Pest

Estimated reading time: 1 minute

There is considerable and justifiable concern over the risks of tin whiskers. However, the same concern is not apparent regarding the dangers of tin pest. This paper will present an overview of both of these reliability concerns by reviewing what is known about the mechanisms and the occurrence of both phenomena.

Mitigation techniques will be discussed, and for tin whiskers, the discussion will focus on barriers between the tin and copper base metal, additions of bismuth to the tin, annealing of the tin, designs that minimize tin whisker failure risk, and over-coatings of the tin. For tin pest, the mitigation technique will be primarily adding bismuth or antimony to the tin.

Tin Whiskers

The existence of tin whiskers has been known since the early days of radio. Typically, tin whiskers form in tin plating on component leads, not bulk solder. Numerous, very expensive failures have been caused by tin whiskers; many of these failures were in satellites. NASA has a website devoted to tin whisker failures.

The website is the home of many iconic tin whisker photographs, and is frequently and justifiably referenced when the topic of the risk of tin whiskers is mentioned. But what is the true risk of tin whiskers in today’s products, and what are the mitigation strategies and their effectiveness in handling this threat?

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Editor's Note: This article originally appeared in the February issue of SMT Magazine.