Finite element and phase field simulation methods for homogenization and electromigration properties of solid-liquid low-temperature welding joints

The advanced three-dimensional package of heterogeneous integration technology is currently the most feasible technical way to improve integration. In actual production, the "substrate-paste-ball-substrate"hybrid solder joint is a widely used interconnection process, which selects a low melting point solder paste, a higher melting point of the solder ball, in a temperature range between the melting point of the solder ball and the melting points of the solder paste, the solid-liquid diffusion welding process can be achieved, so that low-temperature welding can be achieved. However, the reliability of solid-liquid diffusion welding joints remains unclear, while the existing simulation means could not predict accurately the existence of Bi segregation in the Sn-Bi system under the high current conditions.In this research, the electromigration properties of the Cu substrate/Sn-Bi solder paste/SAC305 solder ball/Cu substrate interconnect structure were investigated using the finite element method; the phase-field method was used to study the bias of Bi in the Sn-Bi system, and the first to integrate the phase-field equation with the electrochemical migration equation to obtain a more accurate and realistic simulation under high current density conditions.The results showed that in the electromigration failure model, the stress maxima, current density maxima, and temperature maxima are distributed in the current inflow/outflow parts of the solder balls and Cu wires, and after the aging analysis, the holes are mainly concentrated in the current inflow/outflow parts of the solder balls and Cu wires. The high current has a greater impact on the internal microstructure of the solder joint. This work can be applied to the reliability study of electronic packaging structures, which has very far-reaching implications.