What is an SMA connector?

From the structural principle, the connector has three main parts, the contact pair, the insulator, and the shell.

a) The contact pair of the connector. According to the structure, it is divided into pinhole type, tuning fork type, and curved reed type. Most of them include a guide part, a contact part, a mounting part, and a termination part.

b) The main function of the insulator of the connector is to support and fix the contact pair, so that the contact pair is insulated from each other; the additional device of the connector is installed.

c) The housing of the connector. Its main functions are mechanical and environmental protection and shielding; support for installation of insulators; connection and separation of headers; installation of fixed connectors; fixed cable lead-in ends.

SMA connectors are typically connections between pin contacts and hole contacts. We know that the pins or terminals of components generally have a layer of plating, such as lead-tin alloy plating, pure tin plating, nickel plating, silver plating, silver plating palladium alloy, gold plating, and so on. So the contact between components is actually the contact between these plated metals. Of course, the conductivity of different plating metals is different, and the corresponding contact resistance is also different. Generally, the conductivity of gold is better, followed by silver. In the welding process, since welding is actually a process of forming an alloy, the alloy itself is a good conductor, so the reliability of the welding itself is relatively high, unless the welding is poor. However, the connection between the connectors relies on the contact between the surfaces, so it is easy to cause poor contact. The more specific reasons are analyzed as follows.

Whether the contact between two metal surfaces is good or not mainly depends on the material (different metals have different conductivity), contact pressure, and actual contact surface junction. Regarding the types of materials, as mentioned above, the coating materials of general devices are basically made of good conductors, which have little effect on poor contact, but at most affect the contact resistance (of course, it also affects whether it is easy to be oxidized or not). ), so will not be discussed in more detail. Regarding the contact pressure of the connector, the connector relies on the elastic force of the hole contact to give a certain pressure to the pin contact. Generally, the higher the pressure, the better the contact. Of course, generally small and thin orifice contacts are unlikely to provide excessive pressure. And if the elasticity of the hole contact piece itself is not good, the pressure is small and the contact is not so good. At the same time, if the hole contact or pin contact is deformed, the actual contact area will be small, which may lead to poor contact. At the same time, the hole contacts or pin contacts of the connector are of course generally connected to the plastic. If the number of pins is too large, it may cause a deviation in the position of one or several contacts mounted on the plastic. Therefore, the two When a connector is inserted, those offset contacts may not make good contact.