Investigation of tin whisker growth behavior in COTS components under thermal vacuum cycling

Abstract With the growing adoption of commercial off-the-shelf (COTS) components in aerospace applications, the spontaneous growth of tin whiskers from pure tin coatings has emerged as a critical reliability issue. These whiskers, formed as stress-driven, typically single-crystalline structures, are prone to inducing short circuits and electrical discharges in typical space-relevant environments such as thermal vacuum conditions. This study investigates whisker growth behavior in representative COTS components soldered onto printed circuit boards, subjected to both thermal vacuum cycling and air ambient thermal cycling. The experimental results demonstrate that whisker formation was observed in all tested package types under both conditions. 0603-packaged multilayer ceramic capacitors were particularly susceptible, while whiskers tended to emerge at the bent leads of SOP and TO-packaged devices. Under thermal vacuum, ceramic capacitors exhibited significantly longer whiskers, suggesting that the suppression capability of the nickel barrier layer may be limited under such environments. Comprehensive analysis indicates that the primary driving forces for whisker growth include cyclic thermal stresses caused by mismatched thermal expansion coefficients between the coating and substrate, along with localized stress concentrations arising from grain orientation differences. The influence of intermetallic compound (IMC) layers was relatively minor. Additionally, thinner oxide films formed under vacuum conditions promote more rapid whisker growth.