Causes of Contact Faults in Automotive Connectors

Causes of Contact Faults in Automotive Connectors

Based on on-site analysis and experimental data, it can be seen that contact failure is the main failure mode of connectors, accounting for 45.1%. The growth of contact resistance and the instantaneous disconnection of contact points are the main manifestations of fault forms. The main cause of contact failure is the change in contact force. According to the principle of electrical contact, the surface quality decreases. Based on the principle of electrical contact, combined with the material of automotive connectors, the structure and working environment of the above failure mechanism are analyzed:

1. The fit of the contact change connector is achieved through material deformation. Generally speaking, there are elastic components on the cathode component (i.e. socket), while the anode component (i.e. pin) is a rigid component. During the process of inserting into the socket, it causes deformation of the elastic components on the socket, generating positive pressure to maintain contact. Therefore, the reliability of the entire contact pair depends on the performance of the elastic element and the magnitude of the contact force provided. As the usage time increases, the material properties of elastic components will change, and fatigue and stress relaxation will cause the elastic components to lose their original elasticity and plastic deformation. During these changes, the contact force gradually decreases, leading to connector failure. At the same time, the thermal stress generated by car engines can reduce the strength and contact pressure of materials. The creep of automotive connector materials can occur in long-term high-temperature working environments, and the stress relaxation and even different forms of fracture of the materials can lead to fluctuations in contact pressure. It poses a significant threat to the reliability of connectors. During the driving process, due to the influence of road conditions, there will inevitably be bumps. The "bumps" excitation (specifically manifested as vibration and impact) of the connector contact in this external contact point can cause collision and deformation, which may lead to changes in contact force and cause significant resistance waves in the connector. When the contact force changes below a certain range, it can cause instantaneous failure of the connector.

2. The plugs and sockets of friction and wear automotive connectors will move relatively during use. Due to the existence of elasticity, this movement is always accompanied by friction between the contact and the surface. The micro protrusions and depressions on the material surface are affected by shear force during the friction process, and as the degree of friction increases, the magnitude of shear force also increases. When the shear force reaches a certain limit, the surface protrusions will be cut off and then bonded or scattered outside the contact interface of another surface. As the particles move repeatedly between the contact surfaces, the hardness of the bonded particles gradually increases. These high hardness particles can scratch the surface of the material, and long-term scratching can increase contact resistance, leading to electric shock failure and shortening the service life of the connector. The heat generated during friction can accelerate the formation of oxides on the material surface, leading to contact failure with increased contact resistance. Friction and wear usually occur on contacts with low material hardness, minimal strength, and rough surfaces.

In order to reduce the surface quality of the material, it is necessary to apply a layer of metal on the contact surface of the connector to improve the performance of the material. Pollutants such as gasoline stains and road dust and gases scatter on the coating surface to form a film. The presence of molecular polarity and van der Waals forces can induce the adsorption of oxide films, such as carbon dioxide, on the coating surface. The chemical reaction of the material can cause the coating metal to produce an oxide film, such as tin plating on the contact surface. If the contact pressure is not high, it is easy to produce thick and dense oxides. These film layers reduce the area of current flow, leading to increased contact resistance and failure. High temperatures will accelerate the growth of these membranes during adsorption. A gold or silver coating can to some extent prevent the formation and adsorption of these films. Gold has stable chemical properties and is difficult to oxidize in the air. But gold is expensive, has low hardness, and is prone to adhesion and wear, so it cannot guarantee 100% stability of the contact surface quality. Silver has a relatively low price, high hardness, and low adhesive wear. However, silver is particularly sensitive to the sulfur content in the environment. Air only requires a few ppb of sulfur content, which can corrode the silver coating and cause contact failure. During the formation process of these coatings, due to different processes, there are inevitably many small gaps on the surface of the coating. The electrolyte solution in the environment penetrates into the matrix material through these small gaps. Due to the difference in electrode potential between the substrate material and the coating material, the primary battery reacts under the action of these penetrating electrolytes, forming corrosion products. These corrosion products extend outward from the gap, leading to contact failure.