Effect of in-situ formed Pr-coated Al2O3 nanoparticles on interfacial microstructure and shear behavior of Sn-0.3Ag-0.7Cu-0.06Pr/Cu solder joints during isothermal aging

Abstract

Our previous research has already demonstrated the positive effect of in-situ formed Pr-coated Al2O3 NPs by developing a novel method of simultaneously doping 0.06 wt% surface-active rare-earth (RE) Pr and 0.06 wt% Al2O3 nanoparticles (NPs) into Sn-0.3Ag-0.7Cu solder. It not only addressed the issue of poor interface bonding between ceramic reinforcement (Al2O3 NPs) and solder, but also simplified the most-used modified technology of pre-decorating ceramic NPs with metals to enhance interface bonding. In this study, we focused on investigating the effect of in-situ formed Pr-coated Al2O3 NPs on the evolution of interfacial microstructures and resultant shear forces of the joints soldered with SAC0307-0.06Pr-0.06Al2O3 during solid state aging. The experimental results were compared with those of Sn-0.3Ag-0.7Cu-0.06Pr and Sn-0.3Ag-0.7Cu-0.12Al2O3. It was found the joint soldered with SAC0307-0.06Pr-0.06Al2O3 possessed a delayed growth of interfacial Cu6Sn5 IMCs and an enhanced shear force. This is attributed to a synergistic relationship established between Pr atoms and Al2O3 NPs, in the form of Pr-coated Al2O3 NPs, which effectively pinned the growth and development of interfacial IMCs during high temperature aging treatment. Theoretical analysis showed that the growth constants of total interfacial IMCs (DT) at the SAC0307-0.06Pr-0.06Al2O3/Cu interface was approximately 0.64 × 10−10 cm2/s, about 47.1% and 37.3% smaller than those at the interfaces of SAC0307-0.06Pr/Cu (1.21 × 10−10 cm2/s) and SAC0307-0.12Al2O3/Cu (1.02 × 10−10 cm2/s). Even after 840 h' aging treatment, the fractograph of the shear failure joint soldered with SAC0307-0.06Pr-0.06Al2O3 still exhibited a typical ductile fracture with smaller dimples than that soldered with SAC0307-0.06Pr.