SMTA International Conference Proceedings


Authors: Ronald C. Lasky, Ph.D., PE
Company: Dartmouth College / Indium
Date Published: 9/26/2004   Conference: SMTA International

Abstract: The phenomenon of tin pest has been known for hundreds of years. It was observed in pewter in the 18th century. There is even historic debate as to whether or not tin pest destroyed the buttons on Napoleon’s army on its disastrous return from Russia in the early 19th century. Tin pest can occur in some high tin-bearing alloys at temperatures below 13oC. The "normal" white (beta) tin, with a density of 7.31 g/cm2 , is slowly converted into gray (alpha) tin with a much lower density of 5.77 g/cm2. This transformation and resulting expansion causes the tin to essentially crumble as shown in the photos below.

Some may argue that tin pest is not much of a concern for lead-free soldering since most electrical devices would not see such low temperatures. However, automobile electronics and cellular phone base stations could succumb to the effect. In light of this concern, this paper will review what is known about tin pest, suggest how this information affects the lead-free assembly industry and recommend future work to clarify any remaining concerns.

Key words: Tin Pest, lead-free solder, and tin whiskers.

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