Effect of intermetallic compound thickness on mechanical fatigue properties of copper pillar micro-bumps

摘要

As the continuous miniaturization of integrated circuits (ICs), 3D integration technology becomes one of mainstream methods, in which copper pillar micro-bumps play significant role in the interconnection. In this paper, the effect of intermetallic compound (IMC) thickness on mechanical fatigue properties and fatigue life of Cu pillar micro-bumps was systematically investigated. Specifically, different IMC thicknesses between interconnected micro-bumps were obtained along with the treatment of isothermal aging at 150 degrees C under different time duration. Additionally, a series of mechanical shear fatigue tests were carried out on micro-bumps with variation in shear type and shear load, which indicated that the fracture toughness degraded with the growth of IMC thicknesses. Furthermore, the initiation and propagation of micro-cracks in the interconnection interfaces was characterized using SEM. It was found that different fracture modes were presented with respect to different IMC thicknesses of micro-bumps. Finally, the fatigue life of micro-bumps was calculated based on shear fatigue experiments as well as predicted by Coffin-Manson fatigue model, which implicated that experiments and simulations were in agreement with the trend of fatigue life of micro-bumps against different IMC thicknesses. These results in this work could provide useful insights to improve the quality and reliability of interconnection using copper pillar micro-bumps in 3D integration.