A Study Of Sn-9Zn Lead-free Electronic Solder And Its Improvement By Alloying

Development of lead-free solders has been an urgent task in electronics and materials industry because of the prohibition of lead-containing solders by legislations of environment concern and the requirement of high-density integration development of microelectronics. Eutectic or near eutectic Sn-Ag-Cu alloy has been recommended as the major current substitute of Sn-Pb solders. However, eutectic Sn-9Zn has gained much attention because of its low cost, favorable melting point and good mechanical properties, and is considered as the prototype of the major lead-free solder of the next generation. However, Sn-9Zn alloy is poor in wettability, and this has hindered its applications.On the basis of summarizing the study of Sn-9Zn modification by microalloying and their mechanisms, we put forward a new idea to improve the wettability of Sn-9Zn by two nonmetallic active additives, P and S. Experiments were carried out including the preparations of various Sn-9Zn-based alloys, the spreading tests and dipping tests to evaluate their wettability to Cu. It was found that P and S could significantly improve the wettability of Sn-9Zn to Cu. The maximum improvement is achieved by 0.5 wt.% P or 0.5 wt.% S addition (their factual compositions are 0.156 wt. % and 0.243 wt. %, respectively), which surpasses the reported results in literatures. Although 3 wt. % Bi exhibits better imprdvement, it deteriorates mechanical properties of the alloy due to its brittlement. The results also show that the combination additives of S with Bi and Cu can promote the improvement to some extent, while the combination with P can not, which suggests the different mechanisms of S, Bi, Cu and the same mechanisms of S and P to improve the wettability. Deoxidation effect of P in Sn-9Zn melt was confirmed by the application...