Contact resistance test
Project introduction
Contact resistance is the resistance of current flowing through a closed pair of contacts. This type of measurement is performed on components such as connectors, relays and switches. Contact resistance testing can understand the connection quality of the circuit and its conductive properties, and avoid dangerous overheating of the contacts.
Contact resistance formation principle
Observe the surface of the connector contact under a microscope. Although the gold plating layer is very smooth, a 5-10 micron protrusion can still be observed. You will see that the contact of a pair of plugged contacts is not the contact of the entire contact surface, but the contact of some points scattered on the contact surface. The actual contact surface must be smaller than the theoretical contact surface. Depending on the smoothness of the surface and the size of the contact pressure, the difference between the two can be up to several thousand times.

The actual contact surface can be divided into two parts: one is the part where the real metal directly contacts the metal. That is, the contact micro-points between metals without transition resistance, also known as contact spots, are formed after the interface film is destroyed by contact pressure or heat. This part accounts for about 5-10% of the actual contact area. The second is the part that contacts each other after the contact interface is contaminated with a thin film. Because any metal has a tendency to return to its original oxide state.

In fact, there is no truly clean metal surface in the atmosphere. Even a very clean metal surface will quickly form an initial oxide film of several microns once exposed to the atmosphere. For example, copper only needs 2-3 minutes, nickel about 30 minutes, and aluminum only needs 2-3 seconds to form an oxide film with a thickness of about 2 microns. Even the particularly stable precious metal gold will form an organic gas adsorption film on its surface due to its high surface energy. In addition, dust in the atmosphere will also form a deposition film on the surface of the contact. Therefore, from a microscopic analysis, any contact surface is a contaminated surface.
Factors affecting contact resistance
1. Contact form
2. Contact pressure
3. Smoothness of the contact surface
4. Stability of contact resistance in long-term work
5. Temperature
6. Material properties
7. Use voltage and current
Test requirements
1. Use a 300V insulation resistance meter for testing.
2. The contact resistance of the product to be tested should be less than 1Q.
3. The test product must be more than 5PCS.
Test instructions
1. Passing the contact resistance test does not mean reliable contact. The test proves that only testing the static contact resistance to see if it is qualified cannot guarantee reliable contact in a dynamic environment.
2. The contact resistance is mainly affected by factors such as contact material and surface condition.