Effects of Joule heating on the impact behavior of lead-free Sn-based solder joints

Charpy impact behaviors of eutectic SnBi solder joints with and without presence of Joule heating effect were investigated by employing a pendulum-type impact tester. The temperature rise induced by Joule heating effect at joined region can reach to 6.2°C and 1.7°C when the applied electric current was 10 A and 5 A, respectively. In addition, the temperature distribution of solder joints during the steady-state heat conduction was more uninform due to the sufficient mass of Cu substrates at two sides. Most important, the impact absorbed energies were the same regardless of how much of electric current was applied. The microstructure observation confirmed that the fracture mechanism was the same between the solder joints with and without presence of Joule heating effect. The ultimate results suggested that the weakness of solder joint was located at the interfacial layer where stress concentration possibly arose due to the interfacial reaction and the appearance of the Cu6Sn5 and Bi brittle phases.