Factors affecting the reliability of automotive connectors

Factors affecting the reliability of automotive connectors

There are many factors that affect the reliability of connectors. Domestic and foreign scholars have analyzed and discussed most of the factors, and can summarize various factors. The reliability of most connectors is mainly related to the spot shape, positive force, fit mode, contact smoothness, and material properties between the contacts in terms of structure; The working environment is mainly related to the ambient temperature Environmental pollution is related to load frequency.

The difference in spot shape and spot shape can lead to differences in diffusion resistance. The resistance value of circular spots is related to the radius. The resistance value of rectangular spots depends on the aspect ratio of the spots, while circular spots depend on the outer ring radius and ring thickness. The square circular spot is similar to the circular spot, and its contact resistance value is related to the ring thickness and side length. The transmission performance of these spots is also different. For example, the contact resistance values and minimum values of square circular spots with the same contact area at the copper metal interface are followed by circular spots, followed by circular spots, with square spots having the highest resistance.

2. The mating mode of connectors can be divided into point contact, line contact, and surface contact forms. Different forms correspond to different numbers of spots, with the least number of contact spots during point contact, which is caused by point contact. According to Holm's theorem, the more contact spots there are, the smaller the contact resistance. The contact resistance value is the highest, the surface contact spots are the most, and the contact resistance is the smallest. The line contact spot and contact resistance value are the middle value of the two. The size group of film resistance should be related to the pressure at the contact point. Under equal pressure conditions, the pressure at the contact point is the highest and the film layer is most likely to be damaged. In terms of membrane resistance, the electric contact method is smaller than the wire contact method, and the surface contact method is the largest.

3. Due to the uneven roughness of the connector contact surface, the material will undergo a certain degree of plastic deformation under positive pressure, which will expand the contact area and reduce the contact resistance. The contaminated film on the contact surface of the connector will rupture under a certain size of positive force, greatly reducing the resistance value of the film. Therefore, to a certain extent, high contact pressure is the key to ensuring the reliability of connectors.

4. Contact smoothness

The effect of the smoothness of contact points on contact resistance is essentially the effect of the number of contact points. If the surface of the mating plane is rough, the micro bumps on the material surface are easily in contact with each other, creating more contact points and reducing contact resistance. At the same time, these uneven protrusions also serve to remove the oxide film layer and reduce the resistance of the film layer. For finely machined contact surfaces, the number of contact points is often low, and the contact resistance value is higher than the roughness. However, in terms of stability, the smoothness of the surface performance is good.

5. Material properties The electrical resistivity and hardness of materials are key factors determining contact resistance. Low resistivity and soft materials are the key to ensuring low contact resistance. The chemical properties and high temperature resistance of materials determine their reliability in complex external environments. Metal surfaces with stable chemical properties are less prone to producing fouling films, while metals with good high-temperature resistance can resist material softening and stress relaxation caused by high temperatures.

6. Working temperature, current, friction, and environment are the heat sources for temperature rise of connectors. Under this high temperature, the hardness of metal materials will decrease, which will increase the actual contact area and number, and the contact resistance will also decrease. Usually, the electrical resistivity of materials increases to a certain extent in high-temperature environments, followed by an increase in contact resistance. The contact area and resistivity eliminate each other in high-temperature environments, and their effects cancel out each other, with negligible impact on contact resistance. However, the influence of temperature on membrane resistance cannot be ignored. High temperature catalyzes chemical reactions on metal surfaces, accelerates the production of oxides and the diffusion of metals, thickens the oxide film, and increases contact resistance. During the operation of a car, the engine generates a large amount of heat, so the car needs to dissipate heat to ensure that the connector operates within an acceptable range.

7. The impact of environmental pollution on connectors is manifested as chemical corrosion and electrochemical corrosion. Chemical corrosion mainly occurs in environments that pollute gases (such as oxygen, sulfur dioxide, chlorine, etc.), The connector generates chemicals under the chemical action of these gases, resulting in an increase in resistance. Unlike chemical corrosion, electrochemical corrosion usually requires the participation of electrolyte solutions to occur. Two types of metals with different electrode potentials generate potential differences in conductive solutions, and positive and negative ions move in an electric field, causing galvanic reactions to corrode the metal. Hydrogen analysis corrosion and oxygen absorption corrosion are the most common types of electrochemical corrosion.

8. The difference between load frequency and DC current transmission is that the connector will generate skin collection effect (current gathering on the surface of the conductor) when transmitting AC current, limiting the penetration depth of the electromagnetic field and increasing the contraction of the electrical group. This effect is more pronounced at higher load frequencies.