Experimental Research On The Welding Failure Phenomenon Of Contact Material Used In Micro Relays

Typical micro relays represented by TO-5 are widely used in electronic circuits because of their small size,high reliability and compatibility with integrated circuits.However,the mechanism of welding failure phenomenon of TO-5 relays has still been unknown.In this paper,the effects of mechanical parameters on the contact action,the degradation of electrical characteristics and the mechanism of welding failure under resistive load and surge load in the contact electrical endurance test are studied respectively by means of simulation experimental methods.Firstly,a novel experimental setup specially for micro relays which can realize realtime measurement of contact electrical characteristics is developed.The mechanical system is designed to accomplish the accurate clamping of the TO-5 contact pairs and the independent adjustment of the key mechanical parameters including contact gap,contact over-travel and contact position.The hardware system is designed to complete the electrical condition setting during the contact action and the collection and processing of the original signal.The software system is designed to complete the real-time calculation of the characteristic parameters such as arc,bounce,contact resistance and action time,as well as realize the function of LabVIEW interaction including experimental conditions setting and data and waveform display.Secondly,the counterforce characteristic calculation model of the sheet-rod contact pairs is established,and the corresponding relations between the counterforce of moveable spring,the static pressure of contact pairs,the work done of the spring counterforce and the contact gap,contact over-travel,the height ratio are obtained.Parallel controlled experiments are carried out by changing the above mechanical parameters to study the effects of various mechanical parameters on the electrical characteristic parameters during the contact action.Furthermore,the welding failure process during the contact life test under resistive load is studied experimentally.The arc time,release time and steady contact resistance are chosen as characteristic parameters.The differences of degradation law among these parameters are analyzed under the various mode of full charged in the action process,single charged only in the breaking process and single charged only in the closing process.Based on the contrastive analysis of above characteristic parameters,as well as microscopic morphology and element spectrum of the contact surface,the physical process and mechanism of contact welding failure are proposed.Finally,endurance experiments of TO-5 contacts under capacitive surge load are carried out.According to the typical contact voltage and current waveform,the contact action process under capacitive load is analyzed,and the bounce calorific parameter is selected to analyze the degradation process of contact material.Based on the electron microscopic photographs,the generation mechanism of liquid bridges,the degradation mechanism of contact state and the influence of contact form are analyzed,and a complete failure mechanism analysis of contact welding failure is formed.The study not only can be used to the long life design of micro-relays but also the analysis of anti-welding performance for palladium-based alloy contact material.