Experimental Study Of Adhesion Characteristics For Au-plated Contact Materials Of The Microminiature Relay

Au-plated contact material is widely used in electrical contact field such as micro-relay with high reliability presently. However, cold adhesion failure resulted from Au-plated contact material has a significant influence on the quality and reliability of micro-relay. In order to determine the physical mechanism of material cold adhesion and the main influence factors of cold adhesion characteristics, a novel contact adhesion characteristics test system was designed and the cold adhesion characteristics of Au-plated contact material in sphere-plane contact form was deeply investigated by theoretical modeling and experimental analysis.Firstly, a novel contact adhesion characteristics test system was designed in detail. The piezomotor, the grating ruler and the precision slider constitute the actuation unit, and the high precise force transducer was selected as the method to test the contact force, and three linear translation stages were selected as 3D adjustment structure as well as rotary platform selected as angle adjustment structure. At the same time, the system has the function of the adjustment of open circuit voltage and contact current and the function of isolation. Thus, the simulation of flexible making and breaking movement of contact materials used in micro-relay and the real-time synchronous collection for contact force and contact voltage signals were achieved.Secondly, in order to analog and analyze the contact force and surface deformation during gap variation, and obtain the maximum cold adhesion force existing in contact making process, a rough ball-plane elastic contact physical model in millimeter radius of curvature was built, which is based on the Hamaker hypothesis, the Lennard-Jones potential theorem and the GW rough surface mode. Based on this, the influence of surface roughness, spherical radius of curvature, coating material and elastic modulus on maximum cold adhesion force were analyzed theoretically. The method to reduce the cold adhesion force was proposed. At the same time, the calculation of the capillary force in greater humidity environment based on Laplace equation was made, which was compared with Van der Waals forces.Thirdly, the cold adhesion force of gold-plated contacts during making and breaking process was researched. The cold adhesion characteristics of gold-plated contacts was observed by 10,000 cycles of simulating action. In order to obtain effective measures to reduce cold adhesion force, the influence of surface roughness, spherical radius of curvature, contact pressure and coating material on cold adhesion characteristics were emphatically analyzed.Finally, the contact force and the contact voltage in gold-plated contacts making and breaking process under load was researched to obtain the maximum adhesion force and the adhesion resistance. The change relation between the maximum adhesion force and the adhesion resistance was analyzed by continuous experimental. In order to obtain the proper condition of the cold adhesion failure detection, the adhesion characteristics of gold-plated contacts for open circuit voltage range of 30 m V~28V and contact current range of 30μA~100m A was studied experimentally.The novel test rig developed in this paper can provide an experimental platform for the evaluation of material adhesion characteristics, and the research findings are useful for detecting and analyzing the cold adhesion failure phenomenon which occurred in micro-relay.