Dependance of electric conduction on film thickness of conductive adhesives

The effect of film thickness on the conduction behavior of electrically conductive adhesives is presented. For comparison purposes, an analytical relation is developed to predict three dimensional resistivity of particle filled conductive adhesives. This analysis reveals that the adhesive's resistivity depends on parameters, m, representing an average contact number and, Si, representing the average length of conductive paths between the conductive particles incorporated in the adhesive matrix. Both the parameters m, and Si are functions of the conductive particle volume fraction /spl phi/, and these functional relations are developed by computer simulation for the cases of spherical particles in three dimensional (3-D) and two-dimensional (2-D) contact. The latter (2-D) case represents thin film applications. The computer simulation utilized reveals that the average length of conductive paths in the planar direction of the 2-D case is much larger than that for the 3-D case. This leads to an anisotropic electric conduction case for 2-D thin film applications where the resistivity values in planar directions are much larger than encountered in 3-D measurements for the same adhesive material. This behavior is illustrated using four different commercial conductive adhesives containing silver flakes.