ELECTRICAL CONDUCTION MODELS FOR ISOTROPICALLY CONDUCTIVE ADHESIVES

Abstract

An electrical conduction model was developed by understanding the microscopic conduction between the Ag flake particles and macroscale conduction explained by the percolation theory. The contact resistance between Ag flakes is mainly contributed by constriction resistance and tunneling resistance. The constriction resistance is controlled by the actual contact spot area (metallic contact), which is dependent on the contact force between flakes. The tunneling resistance is dependent on a barrier film thickness. Large contact pressures may cause a break of the tarnish or organic films on the flakes and induce new metallic contacts. The material hardness, pressure between particles and particle contact sizes are important parameters controling the contact resistance.Computer simulations were performed to predict the percolation threshold and particle size effects. Resistivities of the composites were calculated by resistor network simulations incorporating contact resistance and particle size distribution effects. The model predicts that the resistivity decrease with the stress developed during the cure process of the conductive adhesives and with broad particle size distributions.