Dislocation assisted diffusion: A mechanism for growth of intermetallic compounds in copper ball bonds

A combination of Finite Element Analysis (FEA), Molecular Dynamics (MD) simulation and analytical formulation is employed to predict the thickness of Intermetallic Compounds (IMCs) right after ball bonding of copper wire to an aluminum pad. The IMCs growth is related to the enhanced diffusion through the dislocations that are generated in the aluminum pad during the bonding process. Dislocation density and diffusional constants are estimated from the results of the FEA and MD simulation and used to calculate the thickness of IMCs that can form through dislocation-assisted diffusion. It is shown that dislocations have a strong effect on controlling diffusional processes that lead to IMC growth. Results are compared with independently acquired experimental data in the literature. The good agreement between the computed and experimental results supports the validity of the proposed mechanism.