Pulse electric current induced interfacial ductile phase on improving the mechanical properties of the Au20Sn/Cu solder joints

Forming ductile phase is an effective way to release stress localization and suppress crack initiation in interfacial reaction products, which improves the mechanical properties of solder joints. In this work, an FCC (face-centered cubic) structured solid solution, rather than the (Au, Cu)₅Sn, was generated in the Au–Sn/Cu joint via applied pulse electric current of 330, 360 or 380 A current. Particularly, the highest shear strength of 55 MPa was achieved when a uniform FCC phase formed adjacent to the substrate after applying 360A current. Low intensity induced a loose but more FCC phase and the high intensity induced the formation of a more brittle Au₅Sn phase. Different durations contributed to the good plasticity of the joints. Current provides the extra Gibbs energy, ΔG_e, decreasing the thermodynamic barrier and making for the nucleation of the FCC phase. The FCC phase releases the stress location concentration and suppresses the crack formation, which improves the mechanical properties of the solder joints. Applying pulse electric current facilitates the generation of a solid solution FCC phase in the interfacial layer, providing a novel insight into improving the interfacial layer.