Package-level multiphysics simulation of Cu-Al WB corrosion under high temperature/humidity environmental conditions

Copper wire has found extensive applications in microelectronics packaging industry due to its low material cost, advanced electrical, mechanical and thermal properties compared to gold wire. Studies have shown that copper wire performs better than gold wire under high temperature operational conditions as there is little or no kirkendall void formation at Cu-Al wire bond interfacial area. However, when functioning under high humidity conditions, Cu-Al wire bond is more susceptible to bond interfacial corrosion compared to Au-Al wire bond. Experimental results on high humidity reliability of Cu-Al wire bond show that galvanic corrosion at ball bond interface is one of the main causes of failure. Despite reliability performance of wire bond being a constant research subject for decades, there is no time-to-failure model available to describe progression of corrosion. In this paper, a COMSOL multiphysics package level of Cu-Al wire bond corrosion model is developed. The package level model focus on capturing the progression of corrosion as a result of mold compound degradation, chlorine transport and micro-galvanic corrosion. The model is characterized by Nernst-Planck equation and interfacial electrolytic corrosion. Three-electrode electrochemical polarizations are performed to quantify the corrosion rate of wire bond. Diffusion cell experiment and molding compound degradation experiments are performed to quantify the diffusion rate of chlorine and the release rate of chlorine in a particular type of molding compound. Those experimental results are then incorporated into COMSOL multiphysics software to simulate the corrosion process and calculate lifetime of Cu-Al wire bond. The simulation results are then verified by the experimental results.