Hot air leveled tin: solderability and some related properties

Pure hot-air-leveled tin coatings on copper alloy substrates were stored at room temperature for up to four years and then tested for solderability. The solderability of these aged coatings was found to be very good. The intermetallic compound growth rates at lower temperatures were determined to be considerably lower than in electroplated tin coatings. This was attributed to the very large grain size of the tin layer. It was demonstrated that intermetallic growth is significant at the grain boundaries only, which accounts for the overall low growth rates. The whiskering tendency of hot-air-leveled coatings was assessed using tests designed to promote rapid whisker growth. No whiskers or whisker-related features were detected. The grain structure of hot-air-leveled tin, particularly the very large grain size, is the most likely reason for the absence of whiskers