Percolation constraints in the use of conductor-filled polymers for interconnects

The properties of composite systems are understood in terms of percolation phenomena; when a sufficient amount of conductive filler is loaded into an insulating polymer matrix, the composite transforms from an insulator to a conductor, the result of continuous linkages of filler particles. The critical volume fraction at which this transformation occurs, V/sub c/, is the focus of the investigation reported. The concentration is on the properties of some silver-filled silicon rubber composites, and it is shown how the artificial percolation restrictions affect both the critical volume fraction and the resistivity of the composite. A computer simulation of the two-dimensional case shows that these restrictions affect V/sub c/ in a predictable manner. An empirical method of predicting V/sub c/ for non-restricted systems is presented.<>