The basics of connectors!

1. The role of the connector

Connectors, also known as connectors, are mainly used to provide convenient electrical plug-in connections in electronic products and power equipment. They are widely used in electronic equipment, which greatly improves the production and maintenance efficiency of electronic products. Since a large number of plug-in connections are used, the reliability of the connection and the size of the contact point resistance are more and more important to the quality of the product. Use connectors.

2. Connector structure and product classification

(1) Basic structure of the connector

①Contact. It is the core part of the connector to complete the electrical connection function. Generally, a contact pair is formed by an anode contact piece and a cathode contact piece, and the electrical connection is completed by the insertion of the negative and positive contact pieces.

The anode contact is a rigid part, and its shape is cylindrical (round pin), square column (square pin) or flat (insert). The anode contact is generally made of brass and phosphor bronze.

The cathode contact piece is the jack, which is the key part of the contact pair. Relying on the elastic structure, the elastic deformation occurs when the pin is inserted to generate an elastic force to form a close contact with the male contact piece to complete the connection. There are many types of jack structures, including cylindrical type (split slot, necking), tuning fork type, cantilever beam type (longitudinal slotting), folding type (longitudinal slotting, “9″ shape), box-shaped (square jack) ) and double-sided wire spring jacks, etc.

②Insulator. The insulator is also often referred to as a base or a mounting plate. Its function is to arrange the contacts in the required position and spacing, and to ensure the insulation performance between the contacts and between the contacts and the housing. Good insulation resistance, withstand voltage performance and ease of processing are the basic requirements for selecting insulating materials to be processed into insulators.

③The shell. The shell, also known as the shell (depending on the variety), is the outer cover of the connector, which provides mechanical protection for the built-in insulating mounting plate and pins, and provides the alignment of the plug and socket when they are mated, thereby securing the connector to the on the device.

④Appendix. Accessories are divided into structural accessories and installation accessories. Structural accessories such as retaining rings, positioning keys, positioning pins, guide pins, connecting rings, cable clamps, sealing rings and gaskets, etc. Mounting accessories such as screws, nuts, screws and spring rings. Most of the accessories have standard parts and general parts.

(2) Connector product classification

From a technical point of view, there are only two basic division methods for connector product categories: according to the shape and structure, it can be divided into circular and rectangular (cross-section); according to the operating frequency, it can be divided into low frequency and high frequency (with 3MHz as the boundary).

According to the above division, the coaxial connector belongs to the circle, and the printed circuit connector belongs to the rectangle (from a historical point of view, the printed circuit connector is indeed separated from the rectangular connector into a class), and the current popular The cross section of the rectangular connector is trapezoidal, which is approximately rectangular. The division of low frequency and high frequency with 3MHz as the boundary is basically the same as the frequency division of radio waves.

3. The basic performance of the connector

The basic performance of connectors can be divided into three categories: mechanical performance, electrical performance and environmental performance.

(1) Mechanical properties

As far as the connection function is concerned, the insertion force is an important mechanical property. The insertion force is divided into the insertion force and the extraction force (the extraction force is also called the separation force), and the requirements of the two are different.

Another important mechanical property is the mechanical life of the connector. Mechanical life is actually a durability index, which is called mechanical operation in the national standard GB5095. It takes one insertion and one extraction as a cycle, and judges whether the connector can normally complete its connection function (such as contact resistance value) after the specified insertion and extraction cycle.

The plug-in force and mechanical life of the connector are related to the contact structure (positive pressure), the coating quality of the contact part (sliding friction factor), and the dimensional accuracy (alignment) of the contact arrangement.

(2) Electrical properties

The main electrical properties of the connector include contact resistance, insulation resistance and electric strength.

①Contact resistance. High quality electrical connectors should have low and stable contact resistance. The contact resistance of connectors varies from a few milliohms to tens of milliohms.

②Insulation resistance. A measure of the insulation performance between electrical connectors and between contacts and housings, ranging from hundreds of megohms to several gigaohms.

③ Electric strength. Dielectric strength, also known as withstand voltage and dielectric withstand voltage, characterizes the ability of the connector to withstand the rated test voltage between the contacts or between the contacts and the shell.

④Other electrical properties. The electromagnetic interference leakage attenuation is to evaluate the electromagnetic interference shielding effect of the connector, and the electromagnetic interference leakage attenuation is to evaluate the electromagnetic interference shielding effect of the connector, which is generally tested in the frequency range of 100MHz and 10GHz.

For RF coaxial connectors, there are also electrical indicators such as characteristic impedance, insertion loss, reflection coefficient and voltage standing wave ratio. Due to the development of digital technology, in order to connect and transmit high-speed digital pulse signals, a new type of connector, namely high-speed signal connector, has appeared. Correspondingly, in terms of electrical performance, in addition to characteristic impedance, some new electrical indicators have also appeared. , such as crosstalk, propagation delay, and skew.

(3) Environmental performance

Common environmental properties include temperature resistance, humidity resistance, salt spray resistance, vibration resistance and shock resistance.

①Temperature resistance. At present, the maximum working temperature of the connector is 200oC (except for a few high-temperature special connectors), and the minimum temperature is -65oC. Since the current generates heat at the contact point when the connector is working, resulting in a temperature rise, it is generally believed that the operating temperature should be equal to the sum of the ambient temperature and the contact temperature. In some specifications, the maximum temperature rise allowed by the connector at the rated operating current is clearly specified.

②Moisture resistance. The intrusion of moisture can affect the insulation performance of the connector and corrode metal parts. The constant damp heat test conditions are that the relative humidity is 90%”95% (according to product specifications, it can reach 98%), the temperature is +40±20oC, and the test time is at least 96h according to the product regulations. The alternating damp heat test is more severe.

③Salt spray resistance. When the connector works in an environment containing moisture and salt, its metal structural parts and the surface treatment layer of the contact parts may produce galvanic corrosion, which affects the physical and electrical properties of the connector. To evaluate the ability of electrical connectors to withstand this environment, the salt spray test is specified. It is to hang the connector in a temperature-controlled test box, and spray the sodium chloride solution with the specified concentration with compressed air to form a salt fog atmosphere. The exposure time is specified by the product specification, at least 48h.

④Vibration and shock resistance. Vibration and shock resistance are important properties of electrical connectors, especially in special application environments such as aviation and aerospace, railway and road transportation. . There are clear provisions in the relevant test methods. The shock test shall specify the peak acceleration, duration and shock pulse shape and time for interruption of electrical continuity.

Post time: Jan-13-2022