Although it is generally undesirable for the connector contact surfaces to be in continuous relative motion, due to the increased resistance of fretting corrosion, these surfaces often experience "fretting", which may lead to wear and ultimately lead to connector failure.
What is "fretting corrosion"? This is a degradation mechanism caused by relative sliding motion as low as 3 to 4 nanometers. Fretting refers to the abrasion (sometimes corrosion damage) of the unevenness of the contact surface. Contact motion can cause mechanical wear and material transfer on the surface, often resulting in metal fragments and oxidation of newly exposed metal surfaces. This damage can be caused under load and in the presence of repeated or periodic movement relative to the surface. When corrosion causes high contact resistance at the interface, the function is impaired. Electrical failure is another possible problem. These movements may be caused by vibration or differences in thermal expansion.
By designing a matching contact system to show a higher normal force, fretting corrosion can be minimized, thereby mechanically preventing the occurrence of fretting. This strength is evident in some connection systems. Quick-disconnect tabs and sockets are common examples. However, since it is desired to reduce the insertion force and withdrawal force of the connector, a connector with a high normal force is not always feasible. Another way to prevent fretting corrosion is to design the connector to be floating rather than rigidly fixed contacts. This prevents the introduction of relative movement between the mating contacts. Lubrication can also be used to reduce fretting. Tin coatings are most prone to fretting corrosion and degradation. However, fretting is also a concern for gold-plated contacts.
Lubrication can also be used in connectors to reduce friction, thereby reducing mating force and improving durability. In addition to providing protection against fretting, lubrication has also been successfully used as a pore stopper, and thinner precious metal coatings can be used.
In short, tribology is the study of interacting surfaces in relative motion. Although the connectors are designed to be static (once mated together), relative movement may occur due to vibration or differences in thermal expansion. This tiny movement can cause fretting corrosion and eventually high contact resistance at the mating interface. If this movement cannot be prevented by a well-designed connector, you can choose to lubricate the interface. Lubrication can also be used to reduce friction and wear, increase durability, and act as a pore barrier, potentially allowing thinner plating on contact surfaces.
The above information is provided by FAKRA long female connector factory.