A professional technician should be aware that the surface of the connector contact looks smooth, but a 5-10 micron bulge can still be observed under a microscope. In fact, there is no such thing as a really clean metal surface in the atmosphere and even a very clean metal surface, once exposed to the atmosphere, will quickly form an initial oxide film of a few microns. For example, copper only takes 2-3 minutes, nickel about 30 minutes, and aluminum only takes 2-3 seconds to form an oxide film with a thickness of about 2 microns on its surface. Even especially stable precious metal gold, because of its high surface energy, its surface will form a layer of organic gas adsorption film. Connector contact resistance components can be divided into: concentrated resistance, film resistance, conductor resistance. Generally speaking, the main factors affecting the connector contact resistance test are as follows.
1. Positive stress
The positive pressure of a contact is the force exerted by the surfaces in contact with each other and perpendicular to the contact surface. With the increase of positive pressure, the number and area of contact micro-points gradually increase, and the contact micro-points transition from elastic deformation to plastic deformation. Contact resistance decreases as the concentration resistance decreases. The positive contact pressure mainly depends on the geometry of the contact and the material properties.
2. Surface status
The surface of the contact is a loose surface film formed by the mechanical adhesion and deposition of dust, rosin and oil on the surface of the contact. This layer of surface film is easy to be embedded in the micro pits of the contact surface due to the particulate matter, which reduces the contact area, increases the contact resistance, and is extremely unstable. The second is the pollution film formed by physical adsorption and chemical adsorption. The metal surface is mainly chemical adsorption, which is produced with electron migration after physical adsorption. Therefore, for some products with high reliability requirements, such as aerospace electrical connectors, there must be clean assembly production environment conditions, perfect cleaning process and necessary structural sealing measures, and the use of units must have good storage and use of operating environmental conditions.
Post time: Mar-03-2023