Upon examining the surface of the contact pieces of the line-to-line connector, despite the gold plating being extremely smooth, one can still observe protrusions. It is observed that the contact between a pair of mating contact pieces is not the entire contact surface, but rather the contact at some points scattered across the surface. The actual contact area is necessarily smaller than the theoretical contact area.
Connectors can be divided into two actual contact surfaces: one is the direct metal-to-metal contact area. This is the micro-point of contact with no transitional resistance between metals, also known as the contact spot, which forms after the interface film is broken down by contact pressure or heat. In reality, there is no truly clean metal surface in the atmosphere; even the particularly stable precious metal gold, due to its high surface energy, will form a layer of organic gas adsorption film on its surface. Additionally, dust and other particles in the atmosphere will also form a沉积 film on the contact surfaces. Therefore, from a microscopic perspective, any contact surface is a polluted surface.
The actual contact resistance of a connector should consist of the following components: concentrated resistance, which is the resistance displayed due to the contraction of current lines as the current passes through the actual contact surface. It is also referred to as concentrated resistance or contraction resistance.
Conductor Resistance: When measuring the contact resistance of electrical connector contact pieces, the actual measurements are taken at the terminal ends. Therefore, the contact resistance measured actually includes the conductor resistance of the contact piece and the lead wire itself, beyond the contact surface. The conductor resistance primarily depends on the inherent conductivity of the metal material. The relationship between it and the surrounding environmental temperature can be characterized by the temperature coefficient.
Film Resistance: The film resistance caused by the film on the connector contact surface and other contaminants. Analyzing the condition of the contact surface; the surface contamination film can be divided into a relatively solid thin film layer and a more loose impurity contamination layer. Therefore, it can also be precisely referred to as interface resistance.
In weak signal circuit connections, the set test parameter conditions have a certain impact on the detection of contact resistance. Due to the presence of an oxide layer, oil or other contaminants on the contact surfaces, a film resistance is generated between the two contacting parts. As the film thickness increases, the contact resistance rapidly increases since the film is a poor conductor. The film can be mechanically punctured under high contact pressure, or can experience electrical puncture under high voltage and large currents.
