Studies on moisture-induced failures in ACF interconnection

The anisotropic conductive film (ACF) was applied as an under-fill material to bond the die to the substrate in a flip chip package. However, the package encountered electrical failure in environment tests, especially in autoclave test (AC). Therefore, a generic study on the reliability performance of the flip chip in package using ACF in the AC test environment was carried out. Finite element simulations were used to determine the status of moisture diffusion, and hygro-thermally-induced stresses inside the package. The behaviors of conductive particles were also studied. Simulation results agreed well with lab evaluations. It is found that the mismatch in moisture expansion between metal joints and ACF is a key contributor to the robustness of the package.