A numerical method to determine interdiffusion coefficients of Cu6Sn5 and Cu3Sn intermetallic compounds

A fixed-grid source-based numerical method has been developed to simulate the diffusion-controlled growth of Cu6Sn5 and Cu3Sn intermetallic compounds (IMCs) and other many layers of IMCs. Data fittings of measured thicknesses of the IMCs to the simulated results can be further employed to determine the interdiffusion coefficients for the IMCs. Compared with the existing analytical methods, the present numerical method is not only more accurate, but also applicable to a wider range of experimental results. We report here the detailed formulation of the relevant equations, and compare and validate the present numerical method using experimental thicknesses of Cu6Sn5 and Cu3Sn IMCs from both the existing literature and the experiment of our own. The results obtained provide new insight into the interdiffusion coefficients for the Cu6Sn5 and Cu3Sn IMCs formed between Cu and Sn or Sn-based solders, or other many layers of IMCs formed in similar metal/metal systems.