Effect of Lubrication on DC and RF Electrical Endurance of Gold Plated Contacts Subjected to Fretting Wear

Abstract

Fretting wear induced by vibrations is one of the major failure mechanisms of electrical connectors. Former investigations showed that both DC and RF electrical endurance is directly related to the wear rate of the top conductive layer and the trapping of subsurface oxide debris. A convenient mean to reduce wear rate is the use of lubricants, especially conductive grease. While much work has been done on the lubrication of electrical contacts for DC application, the effect and the potential benefits of lubrication in RF domain are still open questions. The aim of this work is to study the effect of conductive grease lubrication on DC and RF electrical endurance of gold coated electrical contacts. A dedicated workbench was developed to study a double sphere/plane contact under fretting solicitations in dry and lubricated conditions. The simultaneous acquisition of DC electrical contact resistance (ECR) and S-parameters permits to quantify the evolution of DC and RF performance of the device during the fretting test. Experimental results show that grease lubrication significantly reduces coefficient of friction $\mu$. As a consequence the electrical lifetime is considerably extended in the DC domain as contact surfaces are preserved from wear but also oxidation. In RF domain, lubricated contact exhibits stable insertion loss during all the test, yet dry contact shows better performance until a long exposure to fretting solicitations (106 cycles), when wear debris form a homogeneous insulating layer that limits the microwave transmission.