Torque-Driven Grain Rotation in Solder Interconnects under Electromigration for Advanced Packaging: Insights from Phase-Field Simulations

As microelectronic devices continue to scale down, grain morphology and crystallographic orientation of solder interconnects within three-dimensional integrated circuits critically influence the reliability of advanced packaging. Grain rotation induced by high current densities during service alters microstructural evolution pathways and directional transport properties; however, quantitative mechanisms coupling electromigration, anisotropic diffusion, and crystallographic reorientation remain to be further elucidated. In this work, we develop a three-dimensional phase-field framework that integrates the Kobayashi–Warren–Carter model with electromigration-driven atomic transport and electron wind torque to predict grain evolution in Sn solder interconnects. The simulations indicate that anisotropic electrical conductivity and diffusivity promote selective grain rotation: grains initially misaligned with the current direction rotate by up to approximately 15° to align their low-resistivity a -axes with electron flow, whereas favorably oriented grains remain largely stable. By decoupling the effects of grain boundary migration and torque-induced rotation, we show that electron wind torque governs the reorientation dynamics, while electromigration primarily drives directional mass transport. The resulting texture evolution, marked by the gradual elimination of low-angle orientated grains and the emergence of preferred orientations, shows qualitative consistency with trends identified in previous electron backscatter diffraction observations. Furthermore, microstructure-driven current redistribution leads to measurable increases in overall interconnect conductivity during stressing, establishing a positive feedback mechanism that stabilizes the evolved texture. These findings provide a physically grounded computational framework for investigating electromigration-induced grain evolution and rotation mechanisms in next-generation heterogeneous integration and offer mechanistic insight into mitigating electromigration-induced failures through grain structure control.