Electrically isotropic conductive adhesives: an effective contact resistance model for conductivity development

A model for determination of the electrical resistivity of isotropic conductive adhesives and insulator/conductor composites in general is introduced by considering the role of contact resistance between conductive adhesive constituents. Conductive behaviour is considered to depend on the creation of conducting contacts between metallic filler particles instead of increasing in the concentration of metal particles. This paper resolves several previously unsolved issues, including the effect of the volume fraction of filler particles and particle size on the development of conductivity; the observed variation in percolation threshold; and the possibility of occurence of two percolation thresholds. In addition, the predicted pressure dependence of conductive behaviour is fully supported by the experimental observations. The model also predicts that the percolation threshold can be reduced by pressure.