Investigation of bulk resistance for metal-coated polymer particles used in anisotropic conductive adhesive

This work presents a novel method to evaluate the bulk resistance of the Au/Ni coated polymer particles of anisotropic conductive adhesive (ACA) joints, considering the bending of electric streamlines and the nonuniformity of current density in the metal layers of particles. The bulk resistance calculated by this new method and conventional methods are compared and the results show that the values gotten by the conventional methods which assume that the current across the particles distributes uniformly are seriously underestimated. Based on the new method, the effects of bonding force and ACA´s geometric parameters on the bulk resistance are investigated respectively. It is found that the bonding force and Au layer thickness are the most important factors to influence the bulk resistance. Ni layer thickness is also very important to the bulk resistance but less sensitive than the Au layer thickness. It is also found that the polymer core diameter has little effect on the bulk resistance when it is more than 3 μm. Finally, the suitable ranges of all these parameters are recommended to ensure the low stable bulk resistance.