Effects of In addition on the properties of Sn–4Ag–0.5Cu–3Bi–0.05Ni solder

Minor In (0, 0.5, 1, 2 wt%) was doped into the Sn–4Ag–0.5Cu–3Bi–0.05Ni (SACBN) solder to investigate the effects of In on the melting characteristics, wettability and micro-hardness of the SACBN-based solder. In atoms in the solders were more inclined to dissolve into Ag₃Sn and (Cu,Ni)₆Sn₅ intermetallic compounds (IMCs), resulting a slightly coarsening of the eutectic IMCs. Besides, the melting temperature (T_m) of the SACBN decreased to 212.9 °C with 2 wt% In addition, but at the same time the melting range (ΔT) increased to 8.3 °C. Moreover, the addition of In had a beneficial effect on the micro-hardness and wettability of the SACBN-xIn solders. The micro-hardness of the SACBN-2In solder (27.28 HV) was slightly higher than that of the SACBN solder (26.08 HV) due to the refinement of β-Sn grains and solid solution strengthening effect of In element and the micro-hardness of the solder increased with the increase of In content. The interfacial IMC layer in the In-containing solder joints was thinner than that of SACBN/Cu solder joint, indicating the presence of In effectively restraining the growth of the IMC layer. This work suggests that the use of 2 wt% In in the SACBN solder has broad application prospects for the emerging advanced packaging technology.