Contact Resistance Reduction by Matching Current and Mechanical Load Carrying Asperity Junctions

Abstract

This article focuses on the differences in how the contact inter-face surface normal load and current density (J) are distributed across a 'Hertzian style' electrical contact interface. Typically, for a Hertzian contact interface the normal load distribution and the current density distribution are not coincident. The asperity junctions, or a-spots, bearing the greatest surface load are preferentially located in the center region of the apparent contact area. Conversely, the a-spots where the greatest current density is generated are located more in the outer rim of the apparent contact area. One way to overcome this mismatch is to structure the contact interface so that the inner part of the apparent contact area carries no load. Doing this forces the a-spots carrying the greatest load to be located in the same outer rim contact interface area as the a-spots with the greatest current density. Based on numerical simulations and experimental re-sults, it can be shown that constriction resistance of such a contact interface can be significantly reduced relative to a similarly finished standard spherical Hertzian contact interface. The great-est contact resistance reduction (up to a factor of 2) can be simu-lated and measured for the case of mated tin finished surfaces. This is due to the fact that the increased mechanical pressure across the conducting a-spots leads to greater disruption and displacement of surface oxides. This factor does not contribute to contact interface resistance reduction for more noble metal finishes.