The continuous trend toward miniaturization and increased integration density in semiconductor devices has exacerbated electromigration (EM) issue, making it a significant reliability concern in advanced packaging technologies, especially in copper (Cu)-pillar bumps used in 3D integration. This study investigates the EM phenomenon in a Cu-pillar bump structure using the birth/death element method in ANSYS. The model incorporates electro-thermal-structural-diffusion coupling transient simulations to analyze the time-dependent evolution of atomic concentration and resistance under varying experimental durations, model sizes, temperatures and current. The simulation results indicate that increased current and temperature significantly accelerate the formation of voids, leading to earlier EM failure. A comparative study between forward and inverse current reveals differences in the evolution of EM-induced damage, where inverse currents exhibiting lower resistance growth over time. These findings provide valuable insights into the design of Cu-pillar bump structures to enhance EM resistance in advanced packaging technologies.