Microstructure and property of Sn-Zn-Cu-Bi lead free solder

Sn-Zn-Cu-Bi lead free solder is one of promising candidates to replace Sn-Pb eutectic solder because of its low cost, good wettability to Cu, low melt temperature and without toxicity. The microstructure and property of Sn-Zn-Cu-Bi lead free solder has been investigated in this paper. The wettability to Cu substrate of solders with different Bi concent was investigated by spread test. Solder melt temperature was tested by DSC themal analysis. Phases in solder joint were analyzed by x-ray diffraction (XRD). The microstructure of solder was observed by scanning electron microscope (SEM). The compositions of different phases in solder were tested through electron probe microanalysis (EPMA) and EDS. Strength of solder was evaluated by tensile test. Results show that Bi can improve solder wettability and reduce the melt temperature, but decrease the strength of solder. There are Sn and Bi solid solution, β - CuSn, CuZn in solder. No Zn solid solution exists in solder. CuZn phase appears as block in solder. Pure Bi and Sn-Bi eutectic phase present as lamellar texture in solder. CuZn₂, η - Cu₆Sn₅, Cu₅Zn₈ and α - [Cu,Sn] intermetallic compounds appeare at interface.