Evaluation of Effectiveness of Conformal Coatings as Tin Whisker Mitigation

The application of a conformal coat has been considered as a mitigation strategy to prevent unintended shorting events induced by tin whisker formation in electronic products. While various conformal coatings have been shown to be effective at containing tin whiskers on treated coupons, the effectiveness of conformal coating on actual assembled hardware has not been adequately examined. In this study, the ability of six types of conformal coatings to contain tin whiskers was examined through their application to assembled gull-wing lead quad flat package test specimens. Nonuniform coverage of conformal coating on the gull-wing leads was found to be a primary concern. Quantitative image analysis using scanning electron microscopy in backscattered electron mode was developed to aid in quantifying coating coverage. The ability of applied coatings to contain tin whiskers was examined after specimens were subjected to sequential temperature cycling and elevated temperature/humidity conditions as well as exposure to corrosive gases. For all but one coating, tin whiskers were observed to escape areas of relatively thin coating. Parylene C coating was found to be the most effective coating in providing uniform coverage and thickness, and containing whiskers.