Effect of nano-ZnO particles on wettability, interfacial morphology and growth kinetics of Sn–3.0Ag–0.5Cu–xZnO composite solder

The influence of nano-ZnO particles addition on wettability, thermal behavior and interface morphology of Sn–3.0Ag–0.5Cu (SAC305) lead-free solder were investigated in present study. SAC305-xZnO composite solder with five different mass fractions of nano-ZnO particles ranging from 0 to 2.0 wt% were synthesized with SAC305 powder, nano-ZnO particles and flux. Solder joints were soldered in a reflow furnace with the maximum temperature of 255 °C for 7 min and followed by isothermal aging at 170 °C up to 240 h. The results reveal that the wettability improves first and then reduces whereas the thickness of intermetallic compounds (IMCs) layer declines first and then increases with the amount of nano-ZnO particles increasing where the threshold occurs at 0.5 wt% nano-ZnO particles, meaning slight addition of nano-ZnO particles can effectively improve wettability as well as restrain IMCs layer growth. The thermal behaviors of SAC305-xZnO composite solder increases slightly as nano-ZnO particles adds from 0 to 2.0 wt%. Moreover, the diffusion coefficient of solder is 0.92 μm²/h, 0.21 μm²/h, 0.22 μm²/h, 0.37 μm²/h and 0.48 μm²/h in sequence with nano-ZnO particles increased from 0 to 2.0 wt%, revealing nano-ZnO particles can inhibit atoms diffusion so as to suppress IMCs layer. Furthermore, the grain size of Cu₆Sn₅ is observed that it increases with power function of aging time describing as $d=1.70t^{0.38}$. In the end, it reveals that Cu₆Sn₅ grows both longitudinally controlled by volume diffusion as well as transversely in the form of boundary diffusion.