Effect of Conductive Particle Properties on the Reliability of Anisotropic Conductive Film for Chip-On-Glass (COG) Applications

Abstract

Summary form only given. This paper describes the effect of material properties of conductive particle in anisotropic conductive films (ACFs) on the reliability of ACF interconnection for chip-on-glass (COG) application. In order to have reliable interconnection in COG using ACF, there are several factors to be considered. Most important factor is the conductive particle properties; the high number of conductive particles trapped between the bump and substrate pad, less conductive particles between adjacent bumps for ensuring electrical insulation, the electrical conductivity for good electrical interconnection, and low mechanical hardness and high recover rate of conductive particles for reliable contact area during reliability test, etc. We investigated the effect of conductive particle on the COG interconnection using ACF with two different conductive particles. For the conductive particles, the Au/Ni coated polymer particles with 5 mum diameter were used. The mechanical and electrical properties of two different particles including ball hardness, recovery behaviors and electrical resistance were characterized. Two ACFs were fabricated in form of double layered structure, in which ACF and NCF layer thickness is optimized, to have as many conductive particles as possible on bump after COG bonding. The test vehicle of COG driver IC and Au trace patterned glass substrate were used for characterization of the COG interconnection. The electrical resistances of ACF interconnection in COG structure were measured initially and during high humidity and temperature test up to 1000 hours. The result shows that the contact resistance of ACF interconnection is mainly dependent on the electrical property of conductive particles in ACF. The reliability test results indicate that the increase of electrical resistance of ACF interconnection in COG is also more dependent on electrical property than mechanical properties of conductive particles under environmentally harsh condition. The conductive particles wish lower electrical resistance, higher mechanical hardness and lower recovery rate showed better reliability than those with higher electrical resistance, lower mechanical hardness and higher recovery rate. Cross-sectional SEM pictures on COG interconnection shows the deformation of two different conductive particles after the reliability tests. The edge or corner located ACF interconnections in driver IC show less reliable joints due to high absorption of moisture. To ensure the electrical contact property at COG interconnection using ACF, the electrical conductivity of conductive particle is more important, than mechanical properties of conductive particles in high humidity and temperature condition