Effect of Ga on microstructure and properties of Sn-Zn-Bi solder for photovoltaic ribbon

In this study, SEM, EDS, XRD and other test methods were used to study the effects of different Ga contents (0~2 wt.%) on microstructure, electrical conductivity, spreading area and mechanical properties of Sn-9Zn-3Bi solder. The results revealed that the microstructure of Sn-Zn-Bi-Ga solder alloy was mainly composed of β-Sn, Zn-rich, Bi-rich phase and Sn-Zn eutectic structure. The Ga can significantly improve the wettability of Sn-Zn-Bi on the pure copper, the maximum wetting area was 105.3 mm². With the increase of the Ga content the melting point of the solders decreased from 195 ℃ to 177 ℃. In addition, the Ga element can increase the oxidation resistance of solder. Its conductivity showed a decreasing trend with the gradual increase of the Ga content. With the increased of the Ga content the IMC (Intermetallic Compound) of Sn-Zn-Bi-xGa/Cu is only Cu5Zn8 and its thickness decreased remarkably.