Analysis of Trapped Conductive Microspheres in LCD FOG Anisotropic Conductive Film Bonding

FOG(Flexible Printed Circuit On Glass) ACF(Anisotropic Conductive Film) bonding achieves electric conductivity interconnection by ACF material. The conductive microspheres from ACF material are trapped between ITO(Indium Tin Oxides) bumps and substrate pads, which are the fundamental cause of achieving electric conductivity interconnection. Prior work has studied the mechanism of achieving electric conductivity interconnection and the interconnection resistance calculation model, presenting the quantity and distribution of trapped conductive microspheres determine the contact resistance of FOG ACF bonding. But those studies haven't presented the mechanism of trapped conductive microspheres in LCD FOG ACF bonding. In this paper, the problem has been researched by Ripley's K function, K-S(Kolmogorov-Smirnov) test and PPP(Poisson Point Process) theory. It has been proved that the distribution of trapped microspheres in each bump belongs to the random distribution and the distribution of trapped microspheres' quantity can be calculated with PPP module in LCD FOG bonding. Finally, we have analyzed the probability of trapped certain number of conductive microspheres in different conductive microsphere density in ACF material and bumps' size, which is useful to optimize ACF bonding and improve the packaging reliability in LCD module industry.