A Study on the Conductivity Variation of Au Coated Conductive Particles in ACF Packaging Process

Abstract

In the ACF packaging process, a bonding force will be applied to the ACF structure. The finite element analysis is used to simulate the ACF packaging process. Material behavior is assumed to be superelastic for resin, viscoelastic for polymer matrix, and elastic-plastic for metal, such as bump, pad, chip, and Au-film. The axis-symmetric model is employed in FEA simulation with time-varying bonding force and operating temperature. In this study, the parameters, including conductive particle diameter, Au-film thickness, and bonding force, are analyzed with nonliner and temperature-dependent material properties. The simulation results indicate that bonding force and operating temperature have strong effects on the formation of concave on Au-film. In addition, surface wrinkle of Au-film will be induced by the bonding force. Both of the concaving and the wrinkling on Au-film will decrease the contact area between the conductive particle and the bump and the contact area between the conductive particle and the pad. Decrease of the contact area means increase of the total resistance for the ACF structure. The results show that the smaller the conductive particle diameter, the smaller the contact area. Generally, increasing the thickness of Au-film will decrease the contact areas, except at the Au-film thickness of 0.05 μm.