Effects of TiO2 nanoparticles addition on microstructure, microhardness and tensile properties of Sn–3.0Ag–0.5Cu–xTiO2 composite solder

The effects of TiO2 nanoparticles addition on the microstructure, microhardness, and tensile properties of Sn–3.0 wt.%Ag–0.5 wt.%Cu–x wt.%TiO2 (x = 0, 0.05, 0.1, and 0.6) composite solders were systematically investigated. Scanning electron microscope (SEM) was used to observe the microstructural evolution of the composite solders, measure the size of the Ag3Sn grains, and estimate the spacing between the Ag3Sn grains in the solder matrix. Energy-dispersive X-ray spectroscopy (EDX) and X-ray diffractometry (XRD) were used to identify the phases of eutectic areas in the composite solder matrix. Results show that both the average size of Ag3Sn grains and the spacing between the Ag3Sn grains decrease significantly, which might owe to the strong adsorption effect and high surface free energy of the TiO2 nanoparticles. The microhardness is improved by 37% compared with TiO2-free noncomposite solder as the weight percentage of TiO2 nanoparticles is 0.1 wt.%. The improvement is due to the microstructural change of the composite solders, which is in good agreement with the prediction of the classic theory of dispersion strengthening. Tensile tests reveal that the TiO2-containg composite solder alloys have higher ultimate tensile strength (UTS) than TiO2-free noncomposite solder alloy due to solid solution hardening. UTS of solder alloys have a logarithmic increase relation with strain rate ranging from 10−3 s−1 to 10−1 s−1 and decreases with an increase of test temperatures ranging from 25 °C to 125 °C.