Experimental and numberical analysis of misalignment mechanism in anisotropic conductive film assembly

The chip-on-glass (COG) technique using anisotropic conductive film (ACF) has been developed for liquid crystal display (LCD) panels with excellent resolution and high quality for several years. However, many serious manufacturability and reliability issues were observed from previous studies. In those, misalignment between integrated circuit (IC) and glass after COG bonding is considered to be one of cruxes harassing the finer pitch interconnection application. Large gaps between outermost bumps and ACF epoxy, which were formed during the cooling down process, were found after IC shear test and were strongly related with the occurrence of misalignment. In this study, a slice of staggered-bumped LCD module was modeled with the nonlinear elastic-plastic and sequential thermal-mechanical analysis. Based on the qualitative and numerical analysis, this paper presented misalignment formation mechanism and misalignment reduction methods in terms of bonding parameters and emphasis on ACF properties, that is misalignment can be reduced by decreasing temperature difference between bonding head and glass substrate and choosing appropriate ACF with the properties of small elastic modulus, large coefficient of thermal expansion (CTE) and low glass transition temperature (T_g). It is recommended that ACF with low T_g is the priority to improve the misalignment problem and the following is the ACF with small elastic modulus and large CTE