With the development of microelectronic packaging and increasingly specific service environment of solder joints, much stricter requirements have been placed on the properties of lead-free solders. On account of small size effect and high surface energy, nanoparticles have been widely used to improve the microstructure and properties of lead-free solders. Therefore, the composite solders bearing nanoparticles have recently attracted wide attention. This article reviewed the recent research on SnAgCu, SnBi, and SnZn composite solder alloys and introduced the effect of nanoparticles on their microstructure, mechanical properties, wettability, and reliability. The mechanism of nanoparticles strengthening was analyzed and summarized. In addition, the shortcomings and future development trends of nanoparticle-reinforced lead-free solders were discussed, which is expected to provide some theoretical reference for the application of these composite solder in 3D IC package.

The microstructure and properties of a Cu/304 stainless steel dissimilar metal joint brazed with a low silver Ag16.5CuZnSn-xGa-yCe braze filler after aging treatment were investigated. The results indicated that the addition of Ce could reduce the intergranular penetration depth of the filler metal into the stainless steel during the aging process. The minimum penetration depth in the Ag16.5CuZnSn-0.15Ce brazed joint was decreased by 48.8% compared with the Ag16.5CuZnSn brazed joint. Moreover, the shear strength of the brazed joint decreased with aging time while the shear strength of the AgCuZnSn-xGa-yCe joint was still obviously higher than the Ag16.5CuZnSn joint after a 600 h aging treatment. The fracture type of the Ag16.5CuZnSn-xGa-yCe brazed joints before aging begins ductile and turns slightly brittle during the aging process. Compared to all the results, the Ag16.5CuZnSn-2Ga-0.15Ce brazed joints show the best performance and could satisfy the requirements for cost reduction and long-term use.

The tin whisker inhibition in RE-doped Sn-Zn soldered joints was investigated. The results indicated that after aging treatment at 150 °C, with the proper addition ratio of Ga and Nd, no obvious NdSn₃ phase nor tin whisker growth was observed in the soldered joints. By replacing the Sn-Nd phase with a Ga-Nd phase, the risk of tin whisker growth caused by the oxidation of RE-phase was significantly inhibited even in soldered joints with additional excessive contents of Nd. The IMC layer in soldered joints with optimal addition showed a relatively regular shape after aging treatment, making the soldered joint maintain preferable mechanical performance. The results would be available for guiding the study of tin whisker growth inhibition method.

In this study, the effect of appropriate Nd addition on improving the high-temperature reliability of Sn-3.8Ag-0.7Cu (SAC387)/Cu solder joint after aging treatment was investigated. The interfacial microstructure of solder joint was refined with proper addition of Nd. This phenomenon could be explained as the adsorbing-hindering effect of surface-active Nd atoms which blocked the growth of brittle intermetallic compounds (IMCs) in the solder joint. Theoretical analysis indicated that 0.05 wt. % addition of Nd could distinctly decrease the growth constant of Cu6Sn5 IMCs and slightly decrease the growth constant of Cu3Sn IMCs respectively. The shear force of SAC387-0.05Nd/Cu solder joint was evidently improved compared with the origin solder joint. In addition, SAC387-0.05Nd/Cu solder joint maintained excellent mechanical property compared with SAC387/Cu solder joint even after 1440 h aging treatment.

The synergistic effects of Nd and Ga on the microstructure and mechanical properties of ER4047 alloy wires and the resulting MIG(Melt inert-gas welding) joints were investigated. Experimental results show that the hydrogen content in the liquid and solid alloy decreases rapidly and then increases slowly with the addition of Nd in the range of 0–0.8 wt.%. Under the same conditions, the hydrogen content ratio in the solid and liquid is between 1.9 and 2.1. After adding 0.08–0.2 wt.% Nd, the α-Al dendrites and eutectic Si phases in the ER4047 alloys are refined and modified, respectively; the quality index of the cast rod increases and the weld percent porosity of the MIG joint significantly decreases. However, when 0.8 wt.% Nd is added, although the size of the eutectic Si phase reaches a minimum value, a large number of coarse needle-like Nd-rich phases precipitate in the structure. Moreover, Ga inhibits the precipitation of the Nd-rich phases, thus improving the mechanical properties, especially the elongation of the cast rod. When 0.2 wt.% Nd and 0.05 wt.% Ga are added into the alloy wire, the porosity of the MIG joint reaches the lowest value herein, and the tensile strength and face/back bending angles reach their maximum values.