Intermetallic compounds formed in Sn droplet on Cu substrate under the impact of electric currents

The present paper investigates the influence of electric currents on the formation of Sn/Cu intermetallic compounds. Solidification experiments of Sn droplets on Cu substrate were performed under the impact of direct csurrents (DC) and pulsed electric currents (ECP), respectively. The results show that the precipitation of Cu6Sn5 from the Sn/Cu interfacial reaction is significantly enhanced by both DC and ECP. DC promotes the formation of Cu6Sn5 at the interface, whereas ECP triggers the detachment of Cu6Sn5 at the interface and favors the growth of freely floated Cu6Sn5 particles in the bulk Sn melt. Numerical simulations were conducted to calculate the distribution of electric current, induced magnetic field, Lorentz force and forced flow inside the Sn melt. The numerical results show that a strong downwards Lorentz force is generated adjacent electrode bottom owing to the interaction between electric current and induced magnetic field. As a result, a global forced flow is caused inside the Sn melt. It is possible that the forced flow induces the elements transport to promote the precipitation of intermetallic compounds. Moreover, a strong Lorentz force difference between Sn melt and Cu6Sn5 is generated under the application of ECP compared with that of DC, thereby increasing the potential to initiate the detachment of Cu6Sn5.