Connect the contact surface under a microscope, and the gold layer is very smooth, still observed in the convex part of 5-10 microns. Will see the mating contact with a pair of contacts, not the contact of the contact surface, but scattered in some of the points of contact of the contact surface. The actual contact surface must be less than the theoretical contact surface. Surface smoothness and the contact pressure size, with the difference and some up to several thousand times. The actual contact area can be divided into two parts; The first real metal to metal contact parts. Intermetallic contact with micro-point of the transition resistance, also known as the contact pattern, which is formed after the destruction of the interfacial film by the contact pressure or thermal effects. May account for 5-10% of the actual contact area. Second, the parts in contact with each other through the contact surface pollution film. Any metal has returned to the tendency of the original oxide state. In fact, in the atmosphere does not exist a real clean metal surface, even if it is a clean metal surface, once exposed to the atmosphere will soon generate a few microns in the early stages of oxidation film. As long as 2-3 minutes, such as copper, nickel, about 30 minutes, aluminum only 2-3 seconds, the surface can be formed oxide film thickness of about 2 microns. Especially the precious metals gold, because of its surface can be higher, the surface will form a layer of organic gases adsorbed film. In addition, the dust in the atmosphere and also in contact with the surface of the formation of the deposited film. Thus, from the microscopic analysis of the contact surface is a contaminated surface.

In summary, the real contact resistance shall have the following parts:

1) focused on the resistance of current through the actual contact surface, due to the current linear shrinkage (or concentration) displayed resistance. Will be referred to as lumped resistance or shrinkage resistance.

2) film resistance due to contact with the surface film and other contaminants posed by the film resistance. Analysis; surface contamination film can be divided into a solid film layer and a loose layer of impurity contamination from contact with the surface state. Therefore, rather, the film resistance known as the interface resistance.

3) conductor resistance when the actual measurement of contact resistance of the electrical connector contacts in the contact terminals, so the actual measured contact resistance also include the conductor resistance outside the contact surface contacts, and leads to the wire itself. Conductor resistance depends mainly on the conductive properties of the metal material itself, its relationship with ambient temperature to characterize the available temperature coefficient.