Simulation of the Current Density Distribution within Electrical Contacts

This article focuses on contact interface current density distributions (J) simulated by numerically solving the Laplace equation for multiple realistic engineered surface/coating combinations. As force increases after surface contact initiation, constriction resistance changes can deviate from the theoretical power law; R_c ~ F_N^-n. It can be shown that this is due to the nature of how the a-spots cluster as they form across the contact area. It will be emphasized that this knee in the log/log plot of constriction resistance versus normal force is not caused by a transition from elastic to plastic deformation of the surface asperities. It will be shown that the distribution of individual current paths for smooth surfaces results in the highest current density level being located within the outer rim of the real contact area; while rougher topographies show a more evenly distributed current density distribution. The influence on J distribution by normal force, contact radii, roughness, and resistivity for the different contact interfaces is calculated. 3-dimensional simulation/visualization using a measured surface x/y-resolution of ~1.5 μm shows the a-spots numbers vary from about 10 to more than 600 at a x/y-grid resolution 128 × 128 mesh points. Very high current loads can cause a-spots to degrade which can trigger the failure of the whole contact system. A numerical approach to simulate these effects is given. The simulation results are compared with an image of a Ag contact subjected to a over current pulse. A test setup to measure the heat dissipation within a contact interface is proposed and the first results are shown..