The Relationship between Contact Resistance and Roughness (Sq) of a Bi-layered Surface using a Finite Element Model

The application of a structured and rough surface, and the effect the roughness has on contact resistance is considered in an electrical contact application. The surfaces are designed to enhance roughness, with an amplitude parameter (Sq, RMS) of 0.1-1 µm. An established finite element model of a bi-layered rough contact surface is extended to include the pre-processing and analysis of a model rough surface. The application is a gold-coated multi-walled carbon nanotube composite (Au/CNT), designed as a solution for electrical contacts in low current switching applications. To determine the contact resistance for these surfaces, a preliminary step is required to determine the effective resistivity.Model surfaces are compared to a measured rough surface, where the sample length of the surface and the sensor interaction with the measured surface are identified as key parameters. The finite element model provides an output of the interactions between a hemi-spherical ball and the rough Au/CNT surface, with the results shown as a map of the points of contact as a function of the applied force (mN). An automated method of post processing the image data is used to determine the number of contact points and the best fitting radius of the contact area. It is shown that the contact resistance increases with surface roughness (Sq).