Thermomechanical Response of Anisotropically Conductive Film

Anisotropically conductive film (ACF) is a smart electronic packaging material that consumes minimal space for connecting an IC chip to a liquid crystal display (LCD) panel or a printed circuit board. It consists of an adhesive resin and fine conductive fillers such as metallic particles or metal-coated polymer balls. The fillers are compressed and maintained at a certain elastic capability enabling them to conduct between the electrodes. Thus the extent of contact area and the shape of conductive fillers are important factors for determining conductivity. The process of applying ACF is modeled into three consecutive steps, with the stress and deformation states studied by finite element analysis in each step. The first step of the manufacturing process involves compressing the conductive particles with an external load at a temperature of 190 oC, insuring that the matrix resin is at a melting fluid condition. In the second step, we maintain the previous temperature and allow the matrix resin to solidify. Then the load is released allowing the particles to spring back to create tension stress in the bonding resin matrix. The final step allows the bonded and conducting ACF to cool from 190 oC down to room temperature. The state of stress and deformation will be readjusted due to different contraction properties between the filler and matrix resin. The results presented in this paper show that the first step of the process is the key focus in determining the function of the ACF.