Analysis of Microstructure and Mechanical Properties of Bismuth-Doped SAC305 Lead-Free Solder Alloy at High Temperature

SAC305 lead-free solder alloy is widely used in the electronic industry. However, the problems associated with the growth formation of intermetallic compounds need further research, especially at high temperatures. This study investigates the doping of Bismuth into SAC305 in the various compositions of 1, 2, and 3 wt.%. The microstructure in terms of intermetallic compound particles and mechanical properties was examined after thermal aging at temperatures of 100 °C and 200 °C for 60 h. The microstructure examination was observed using scanning electron microscopy, and the chemical composition of each alloy was confirmed with an energy dispersive X-ray. Tensile tests were performed to find the mechanical properties such as yield strength and ultimate tensile strength. The intermetallic compound’s phase analysis was identified using X-ray diffraction, and differential scanning calorimetry was done to study the temperature curves for melting points. Results showed that the addition of Bismuth refined the microstructure by suppressing the growth of intermetallic compounds, which subsequently improved the mechanical properties. The thermal aging made the microstructure coarsen and degraded the mechanical properties. However, the most improved performance was observed with a Bismuth addition of 3 wt.% into SAC305. Furthermore, a decrease in the melting temperature was observed, especially at Bismuth compositions of 3 wt.%.

Contact Angle of Sn-8Zn-3Bi Lead-free Solder Alloy on Copper Substrate

The wettability of Sn-8Zn-3Bi lead free solder alloy on the copper substrate was evaluated via measuring the contact angle of the solder and the substrate. The measured contact angle was then compared to the contact angle of the traditional and widely used eutectic Sn-37Pb solder alloy. Experiments to study the effect of temperature, flux, and surface roughness of the substrate on the contact angle were also carried out. The results show that the contact angle of Sn-8Zn-3Bi on copper substrate decreased as temperature increases. The minimum value of the contact angle obtained was approximately 23° for Sn-8Zn-3Bi. At the same experimental conditions, contact angle of Sn-8Zn-3Bi is higher than that of Sn-37Pb. When three types of fluxes were used, at 230°C, contact angle of Sn-8Zn-3Bi has the smallest value with the MHS37 flux, 25°, and it has the largest value with the zinc chloride flux, 47°. The surface roughness of the substrate has little influence on contact angle of Sn-8Zn-3Bi on copperand the contact angle has changed a few degrees as the roughness changed.