LAUSR

Abstract Low-cost Al2O3 nanoparticles (NPs) are regularly incorporated into lead-free solder to improve its mechanical performance, but the poor wettability of Al2O3 NPs leads to weak Al2O3/solder interface bonding. In this work, a novel idea different from the common solution of pre-coating a metal layer on the surface of NPs was proposed to address the issue of weak interface bonding by simultaneously doping rare-earth (RE) Pr (0.06 wt%) and Al2O3 NPs (0–0.5 wt%) into Sn-0.3Ag-0.7Cu low-Ag solder. The coupling effects of RE Pr and Al2O3 NPs on the wettability, microstructures, shear force and creep resistance of prepared nanocomposite solder were systematically investigated. It was found that the coupling effects were concentration dependent. When the content of Al2O3 NPs was less than 0.06 wt%, a synergistic relationship between free Pr atoms and Al2O3 NPs was established. This is because the surface-active Pr atoms, acting as bridges between Al2O3 NPs and solder matrix, can be spontaneously adsorbed at the surfaces of Al2O3 NPs to in situ form Pr-coated Al2O3 NPs, which have much better wettability than the single Al2O3 NPs. However, increasing the doping content of Al2O3 NPs over 0.06 wt% led to a competitive relationship among free Pr atoms, Al2O3 NPs and Pr-coated Al2O3 NPs, which was probably caused by the emerged Al2O3 agglomerates occupying partial space of grain surfaces. The optimum doping content of Al2O3 NPs in SAC0307–0.06Pr solder was approximately 0.06 wt% and SAC0307–0.06Pr-0.06Al2O3 possessed the best wettability, a well-controlled growth of interfacial IMC layer, the highest shear force (∼61 N) and a superior room-temperature creep resistance with creep stress exponent (n) reaching approximately 11.7.