Formation mechanism of a cathodic serrated interface and voids under high current density

Abstract

In this paper, a Cu/SnAg3.0Cu0.5/Cu solder joint is current stressed under 6 A at 120 °C. After current stressing for 300 h, a serrated interface and voids are observed at the cathode. Current-crowding and thermal-crowding in solder grooves between adjacent Cu6Sn5 grains are found to be responsible for the back-diffusion of Sn and Cu atoms, eventually leading to the formation of a cathodic serrated interface and voids. In addition, the Sn orientation of the solder grooves may also play an important role in the robustness of the cathodic Cu6Sn5 grains and electrode. Our study may provide understanding of electromigration/thermomigration-induced evolution of the Cu/Sn interface under current stressing and provide visual data for interpreting early open-circuit failure of solder joints.