Five, contact resistance 

Contact resistance refers to the resistance that generated by two contact conductors at the contact portion. Two problems should be noted when we selecting.

First, the the connector contact resistance index is actually the contact to the resistance, which includes contact resistance and the contact to the conductor resistance. Usually the conductor resistance is small, so the contact to the resistance is called contact resistance in most technical specifications.

Second, in circuits which connect small signals, pay attention to the conditions under that the given contact resistance indicators are tested, because the contact surface is accompanied by oxide layers, oil stains, stubborn stains or other contaminants, and film resistance is to occur on the surfaces of the two contacts. When the film thickness increasing, the resistance increases rapidly as well, that the film becomes a poor conductor.

However, the film may endure mechanical breakdown under a high contact pressure, or electrical breakdown may occur under large current and high voltage.