Effects of Conductive Particles on the Electrical Stability and Reliability of Anisotropic Conductive Film Chip-on-Board Interconnections

The effects of conductive particles on the electrical stability and reliability of anisotropic conductive film (ACF) joints for chip-on-board applications were investigated. In this paper, two types of conductive particles were prepared. One was a conventional Ni/Au-coated polymer ball, and the other was a Ni/Au-coated polymer ball with Ni/Au-projections. According to the results of a nano-indentation experiment of a conductive particle, the elastic recovery of a single conductive particle decreased as the applied load and the deformation of the conductive particle increased. The evaluated conductive particles which had the same polymer core showed the similar load-deformation behaviors regardless of the existence of Ni/Au-projections. The contact resistances of ACF joints using each conductive particle as a function of bonding pressure were measured, and the results showed that the contact resistances of ACF joints with the metal-projection-type conductive particles were lower and more stable than those with the conventional conductive particles. Especially at lower bonding pressure, ACF joints with the metal-projection-type conductive particles were much more stable and had lower contact resistances than the conventional ACF joints. According to the results of thermal cycling (T/C) reliability test, the metal-projection-type conductive particles also enhanced T/C reliability of ACF joints when compared with the conventional conductive particles.