Finite element analysis of anisotropic conductive film for chip on glass process

Anisotropically conductive film (ACF) is a smart electronic packaging material that consumes minimal space for connecting integrated circuit (IC) chips to a liquid crystal display (LCD) panel or 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 maintain a certain elastic capability while conducted between electrodes. The size of the contact area and the shape of the fillers are important factors in determining conductivity. The process of applying ACF is modeled into three consecutive steps, and the stress and deformation states are studied by finite element analysis in each. In step 1 of the manufacturing process, external load is applied to compress the conductive particles at a temperature of 190°C so that the matrix resin is in a fluid condition. In step 2, an external load is maintained at this temperature to allow the matrix resin to solidify; then, the load is released and the particles spring back to create tensile stresses in the bonding resin matrix. The last step considers the bonded and conducting ACF cooling from 190°C 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 changing the thickness of a coated nickel layer does not clearly affect the conductivity of ACF, and the deformation should be greater than 40% for the stability of conductivity.