Tin whiskers are electrically conductive, crystalline structures of tin that sometimes grow from surfaces where tin (especially electroplated tin) is used as a final finish. They typically grow from lengths of 1-2 millimeters (mm) but have been observed to lengths in excess of 10 mm. They are a serious issue in the electronics world because they have been known to cause short circuits between circuit elements.
While there is no known way to prevent tin whisker growth, there are some mitigation strategies that can be employed to limit their impact on your product. One of the strategies we suggest to use is conformal coating.
HumiSeal® 1B31 is a fast drying, single component, acrylic conformal coating that provides excellent moisture and environmental protection for printed circuit assemblies. It is one of the most popular coating choices and is usually a very cost effective option for a normal conformal coating project.
Based on the results of a NASA study, acrylic conformal coatings were able to penetrate through the coating without offering much resistance. However, even poor coating choices can offer some protection. The conformal coating will protect against a conductive bridge from detached whiskers lying across a pair of coated conductors.
A better choice to mitigate tin whiskers would be to use a thicker, urethane conformal coating. After 11 years, no tin whiskers were found to penetrate the 2 mil thickness of the urethane conformal coating. Instead of penetrating the coating, the tin whisker will act as a pole and “tent” the coating. While this is not ideal, it can still prove to be an effective means of limiting the effects of the tin whiskers.