Corrosion behavior of Sn-Zn-Bi and Sn-Pb-Ag solders in a salt spray test

Most of the commonly used lead-free solders have a high melting temperature. However, in many applications a lower processing temperature would be beneficial. Therefore a demand has arisen for reliable lead-free solder with a lower melting temperature. Among the low temperature lead-free solders, Sn-9Zn and Sn-8Zn-3Bi (wt.%) are suitable candidates for many applications, since they offer good mechanical reliability and melting temperature similar to that of Sn-Pb solders. However, because they contain an active element (Zn), they need to be used with caution, especially in corrosive environments and in high-temperature applications. In this paper the corrosion behavior of Sn-8Zn-3Bi lead-free solder was studied using a salt spray test. The microstructure of the solder was studied at different time intervals during the salt spray test. Sn-36Pb-2Ag (wt.%) solder joints were also studied as reference samples. It was found that Sn-8Zn-3Bi suffered from galvanic corrosion earlier than the Sn-Pb-2Ag solders. However, considerable corrosion was observed after the salt spray test in both solders. Moreover, it seemed that the corrosion performance of Sn-Pb-2Ag solder was better than that of Sn-8Zn-3Bi solder.