Three-dimensional phase-field model of interfacial microstructure evolution of Cu/Sn/Cu solder joints under electromigration

With the development of electronic devices towards miniaturization and multi-functionalization, the solder joint size decreases sharply, causing electromigration (EM) in solder joints to be a serious reliability concern. In this study, a three-dimensional model of Cu/Sn/Cu solder joint is formulated to investigate the electromigration behavior of different cross sections along and perpendicular to the current direction. In the cross sections perpendicular to the current direction, the intermetallic compounds (IMCs) growth and pad dissolution are more likely to occur at the corners of solder joint. The polar effect at the center cross section along the current direction is most evident. The interfacial IMCs growth at low current densities (i.e. 0.8 × 10⁴ A/cm²) follows a parabolic relationship with time, revealing that it is controlled by the concentration gradient. Upon imposition of high current densities (i.e. 1.5 × 10⁴ A/cm²), the interfacial IMCs growth shows a linear relationship with time, which is mainly driven by electromigration. In both the simulation and experimental results, significant pad dissolution and "finger-shaped voids" appear at the IMC/solder interface of the cathode side, while prominent IMCs growth and Kirkendall voids are observed within the IMC layer of the anode side of the solder joint. Additionally, the variation in shape of solder joint morphology has great effect on the electromigration reliability.