Abstract
The interfacial reaction between Sn-Zn solders and Cu in solid-state was examined. The microstructure change of the solders due to heat-exposure at 125°C, 135°C, and 150°C was also examined. In case of Sn-8Zn-3Bi and Sn-9Zn/Cu joints, the Cu-Zn intermetallic compounds at the interface grow by following the parabolic law at initial stage, by the heat-exposure. Much amount of Cu diffuses into the solder layer resulting in the formation of Cu5Zn8 grains. The speed of the phase transformation of Zn phase into Cu5Zn8 of the Sn-8Zn-3Bi/Cu reaction system is higher than that in the Sn-9Zn/Cu system at all temperatures. The voids are found at the solder/reaction layer interface in long time heat-exposure. The Sn-Cu compound and Sn phase which is with a small amount of Zn and Bi are observed at the interface of reaction layer and Cu. On the other hand, Sn-20Zn and Sn-30Zn/Cu joints not to form large voids at interface and can maintain good stability against heat-exposure.
