Effect of coating adhesion and degradation on tin whisker mitigation of polyurethane-based conformal coatings

Tin whisker growth, which may lead to short circuits and current leakage, is a serious issue in electronics components. Polyurethane-based conformal coatings have been seen as an effective candidate to mitigate the tin whisker growth. To better understand the effect of such coatings, this study exposed the tin-plated copper coupons coated with i) moisture cured polyurethane (PU) and ii) dual UV/moisture cured polyurethane acrylate (PUA), for long-term (up to 5000 h) high-temperature and high-humidity (HTHH) storage (85 °C and 85%RH, respectively). After HTHH storage, microstructural developments in the tin layer, coating degradation, tin surface reaction, and coating adhesion to tin surface were analyzed to compare the tin whisker mitigation behavior. In order to improve the coating adhesion, tin surface was also treated with a silane adhesion promoter before coating was applied. Furthermore, the effect of electron beam irradiation was investigated as it degraded the coating properties and adhesion. The results show that maintaining good adhesion and suppressing the degradation of mechanical properties of conformal coatings during various environmental exposures are essential for enhanced tin whisker mitigation.