Effect of Ni 3 Sn 4 Nanoparticles on Grain Refinement in SAC305 Freestanding Solder Balls and SAC305/Cu BGA Joints

Sn-Ag-Cu solder joints have been reported to typically solidify from a single nucleation site, resulting in thesolder joints tend to contain a few number of twinned s-Sn grains and sometimes only one s-Sn grain. Owing to the anisotropy of tetragonal s-Sn, the solder joints will exhibit significant anisotropy in physical and mechanical properties, which will inevitably cause reliability issues. Therefore, it is necessary to develop effective method to refine the s-Sn grains in Sn-Ag-Cu solder joints. In this study, we explored the potential sites for heterogeneous nucleation in refining s-Sn grains by adding 0.5 wt. % Ni 3 Sn 4 nanoparticles into 700 µm SAC305 freestanding solder balls and SAC305/Cu BGA joints. It was found that the morphology ofs-Sn grains in the SAC305 freestanding solder balls and SAC305/Cu BGA joints was beach ball and single grain, respectively. After adding Ni 3 Sn 4 nanoparticles into the SAC305 freestanding solder balls and SAC305/Cu BGA joints, the morphology of the s-Sn was multiple grains and singe grain, respectively. The reason for these phenomena were that the content of Cu was 0.8 wt. % in the SAC305/Cu BGA joints with Ni 3 Sn 4 addition which was higher than 0.5 wt. % in the SAC305 freestanding solder balls with Ni 3 Sn 4 addition. As a result, the Ni 3 Sn 4 nanoparticles could be dissolved completely in the BGA joints and had no effect on the solidification of s-Sn; while partly dissolved in the SAC305 freestanding solder balls and the remaining Ni 3 Sn 4 nanoparticles could be served as nucleation sites for s-Sn.