Bi additions have been reported to improve the wettability and drop-impact performance. Most important of all, it improves the mechanical properties. However, few studies focus on the effect of the Bi addition on mechanical properties and microstructure of intermetallic compounds (IMCs) in solder balls, especially on those properties after current stressing. In this study, to understand the effect of Bi addition, a lead-free Sn-3Ag-0.5Cu-xBi (SAC305-Bi) solder joint with Bi additions from 1 to 3 wt% was used to investigate mechanical property of Sn-rich matrix and microstructure of IMCs in the solder joint after current stressing process. We combined nanoindentation, scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) to analyze mechanical property, and observe the intermetallic compounds of Cu₃Sn, and Cu₆Sn₅ at the interface. The mechanical properties of hardness in Sn matrix is improved by the amount of Bi, where the hardness increases from 0.095 to 0.141 GPa as increasing Bi addition from 1 to 3 wt%. In addition, the growth rate constant of intermetallic compounds of Cu₃Sn is in the range between 0.175 and 0.256, that is, Cu₃Sn is not sensitive to Bi addition. Furthermore, the amount of doping Bi addition enhances the growth rate Cu₆Sn₅, as the rate constant increases from 1.597 to 2.413 with increasing Bi addition from 1 to 3 wt%.

据报道，Bi的添加改善了润湿性和滴落冲击性能。最重要的是，它改善了机械性能。但是，很少有研究关注Bi的添加对焊球中金属间化合物（IMC）的机械性能和微观结构的影响，特别是电流应力后的那些性能。在这项研究中，为了了解Bi的影响，使用Bi含量为1-3 wt％的无铅Sn-3Ag-0.5Cu-xBi（SAC305-Bi）焊点来研究富Sn的机械性能电流应力处理后焊点中IMC的基体和微观结构。我们结合了纳米压痕，扫描电子显微镜（SEM），能量色散X射线能谱（EDS）和电子背散射衍射（EBSD）来分析机械性能，界面处的₃ Sn和Cu ₆ Sn ₅。Sn的硬度的机械性能通过Bi的含量得以改善，其中Bi的添加量从1 wt％增至3 wt％时，硬度从0.095 GPa增至0.141 GPa。另外，Cu ₃ Sn的金属间化合物的生长速度常数在0.175〜0.256的范围内，即，Cu ₃ Sn对Bi的添加不敏感。此外，随着Bi的添加量从1wt％增加到3 wt％，随着速率常数从1.597增加到2.413 ，掺杂Bi的添加量提高了Cu ₆ Sn ₅的生长速率。