There are many reasons for poor contact in electronic products. It may be poor contact within the components themselves, or poor contact when the components are interconnected, or poor contact caused by cold soldering (usually between components and PCB). Poor contact between connectors (connectors) is the most common reason.

Connectors are generally connected through pin contacts and hole contacts. Components generally have a layer of plating at the pins or terminals, such as lead-tin alloy plating, pure tin plating, nickel plating, silver plating, silver-palladium alloy plating, gold plating, etc. Therefore, the contact between components is equivalent to the mutual contact between the plated metals.

Whether the contact between two metal surfaces is good or not mainly depends on the material, contact pressure and actual contact area. The plating materials of general devices are basically made of good conductors, so they have little effect on poor contact.

The surface of the contact looks smooth to the naked eye. In fact, the surface of these contact parts is not smooth. Therefore, when the two contact surfaces are in contact, it is actually a canine-tooth staggered contact between uneven surfaces. Since the shapes and sizes of the convex and concave cannot all match, they are actually only partially in contact when embedded.

When metals are in contact, if there is an obvious external force, the contact state will change. Some devices have poor internal contact, and sometimes a knock may fix it.