An investigation on the ZnO retained ratio, microstructural evolution, and mechanical properties of ZnO doped Sn3.0Ag0.5Cu composite solder joints

In this study, ZnO nanoparticles with different weight fractions (0.1, 0.25, 0.5 and 1 wt%) were successfully incorporated into Sn3.0Ag0.5Cu (SAC305) solder through powder metallurgy method. The retained ratios of ZnO reinforcements were measured, and then their effects on the thermal behaviors, microstructural evolution and mechanical properties of composite solders were systematically studied. The element content analysis revealed that only about 12 % of the initially doped ZnO nanoparticles were retained in the final solder joints. With an increase in the amount of reinforcements, the undercooling of composite solders was decreased while the melting temperature was negligibly altered. Refined β-Sn grains were obtained in the composite solder matrix after addition of ZnO nanoparticles. Moreover, compared to the plain solder joints, the composite solder joints exhibited a lower growth velocity of interfacial intermetallic compounds during isothermal aging. A 17.9 % improvement in microhardness and a 10.1 % enhancement in shear strength were also achieved for composite solder joints after 1 wt% ZnO addition. These promotions are all contributed by the presence of ZnO nanoparticles and refined microstructure in solder matrix.