Effect of fretting wear of connectors regarding phase noise of RF signal: Influence of sliding amplitude and gold coating thickness

High technology domains such as aerospace, aviation and defense require a reliable transmission of RF signals. In these applications, RF connectors are exposed to severe environmental vibrations and are subjected to fretting wear damages. Former investigations on real connectors have shown that fretting wear leads to a dramatic increase of the DC electrical contact resistance (ECR), degrades RF microwave transmission and generates a significant additive phase noise. The present study aims to formalize the correlation between wear mechanisms of top gold layers and the evolution of electrical properties in DC and RF. An original fretting test bench was specifically developed to study a homogeneous double sphere-plan contact under gross-slip regime for different fretting loadings and different conductive films thickness. During the test DC ECR and phase noise are measured simultaneously. To quantify the fretting RF lifetime of the contact, a dedicated phase noise endurance criterion is used (Lm, th = -120 dBC/Hz). This phase noise threshold is shown to correspond to a ΔRth = 0.4 Ω DC contact resistance variation and was related to a quasi-full elimination of gold layer from the fretted interfaces. This experimental investigation suggests that fretting cycle endurance Nc (RF and DC) decreases asymptotically as a function of the sliding amplitude ög* but increases exponentially with the coating thickness e. Elemental analysis and 3d profile measurement demonstrate that the evolution of the electrical properties of the contact is driven by the top gold layer wear rate and the trapping of subsurface oxide debris in the interface induced by the fretting wear of NiP interlayer and CuSn4 substrate.