Mitigation of tin whiskers with polymer coatings

A significant majority of component terminations are finished with electroplated tin. This finish offers a number of process advantages, but does have an intrinsic reliability issue. During ageing of the tin stresses can build in the finish that can result in the growth of a single crystal of tin out of the surface, a so-called tin whisker. Such whiskers can grow to a few hundred microns and cause a short circuit between component terminations. Although great advances in tin chemistry have dramatically reduced the incidence of tin whiskers, no finish is guaranteed as whisker free. This has lead to exploration of mitigation strategies, prime among which is the application of a thin conformal polymer coating. Such coatings have been used extensively for environmental protection, but now they are being explored in the role of mitigation. This project discusses a technique that explores a characterisation route for the performance of polymer coatings. Work with coating chemistry suppliers´ reveals that variation in the mechanical properties of the coatings affects the mitigation potential.