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    3 Major Causes of RF Coaxial Connector Failure
     Feb 23, 2022|View:204

    There are many kinds of RF coaxial connectors, so there will also be many detailed problems in the connection process. This paper will talk about the reasons around the component failure of RF coaxial connector.

    3 Major Causes of RF Coaxial Connector Failure

    Type of RF coaxial connector

    Before understanding various problems, we need to re understand the types of RF coaxial connectors, so as to better understand the problems involved.

    1. Threaded connection type: such as apc-7, N, TNC, SMA, SMC, L27, L16, L12, L8, L6 and other RF RF coaxial connectors. This kind of connector has the characteristics of high reliability and good shielding effect, so it is also the most widely used.

    2. Bayonet connection type: such as BNC, C, Q9, Q6 and other RF RF coaxial connectors. This kind of connector has the characteristics of convenient and fast connection. It is also the earliest connection form of RF connector in the world.

    3. Push in connection type: such as SMB, SSMB, MCX, etc. the connector of this connection type has the characteristics of simple structure, compactness, small volume and easy miniaturization.

    Failure analysis of RF coaxial connector

    We will mainly talk about the failure principle of threaded connection which is widely used and has the most varieties at present. There are generally the following scenarios:

    1. Connection failure

    (1) The connecting nut falls off

    In daily life, some users report that sometimes the connecting nut falls off, which affects the normal work, especially for small connectors, such as SMA, SMC and L6. After our analysis, it is generally caused by the following reasons:

    In order to reduce the cost, the designer misused the inelastic brass seat snap ring material, which made the nut easy to fall off.

    During processing, the groove depth of the nut mounting snap ring is not enough, so the nut will fall off with a little torque during connection.

    Although the material selection is correct, the process is unstable, the beryllium bronze elastic treatment does not reach the hardness value specified in the drawing, and the snap ring is inelastic, resulting in the nut falling off.

    During the test, the user did not have a torque wrench, but used an ordinary wrench to tighten the nut, so that the tightening torque greatly exceeded the specified value of the military standard, so the nut (snap ring) was damaged and fell off.

    (2) Pairing error

    Some customers will mistake the Q9 cable head bought in the market for the BNC cable head commonly used in the world. Because its shape is exactly the same as that of BNC cable head, but the size is slightly different, it is not compatible with imported instrument BNC.

    (3) The inner conductor is loose or falls off

    Some designers divide the inner conductor into two parts at the dielectric support of the inner conductor, and then connect them with threads. However, for small RF RF coaxial connectors, the size of the inner conductor itself is Φ 1 ~ 2mm, the thread is processed on the inner conductor. If the conductive adhesive is not coated on the threaded connection, the connection strength of the inner conductor is very poor. Therefore, when the connector is connected for many times, under the long-term action of torque and tension, the internal conductor thread will loosen and fall off, resulting in connection failure.

    2. Reflection failure

    (1) Reflection increase

    Any kind of connector has a certain service life. Taking SMA connector as an example, the American military standard and Chinese military standard stipulate that its service life is 500 times. This is because after long-term use and repeated plugging for more than 500 times, the pins and sockets have caused varying degrees of wear, and the contact is not the best state. Therefore, the reflection may increase sharply during use.

    (2) Open circuit

    In previous work, it was found that individual users mistakenly connected the n-type 50 Ω plug to the n-type 75 Ω socket. Because the pin diameter of 50 Ω is much larger than the jack size of 75 Ω, the jack size exceeds the elastic limit and cannot be restored to the original size. Others found an open circuit when they used it again. The socket of the original 75 Ω socket has been damaged.

    (3) Short circuit

    When some connectors are sealed and connected to the welding inner conductor, the solder flows to the surface of glass insulator, resulting in total or local short circuit and unqualified performance.

    Electrical contact failure

    Usually, the socket parts should be made of beryllium bronze or tin phosphorus bronze, but a few manufacturers use 59-1 brass as the socket in order to reduce the cost. Therefore, after plugging in and out for one or two times, the socket is in the state of expansion. When connecting the pin and socket again, it will not contact at all, which will also cause problems in use.