Basic knowledge 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 efficiency of production and maintenance of electronic products. Due to the large number of plug-in connections, the reliability of the connection and the size of the contact resistance are becoming more and more important for the quality of the product. Therefore, it is necessary to fully understand the performance of the connector used in order to reasonably and correctly Use connectors.

2 . Common connector physical diagram and characteristic application are shown in Table 1.

Table 1 Common physical appearance and characteristics of connectors

3. Connector structure and product classification

(1) The basic structure of the connector

â‘ Contacts. It is the core part of the connector to complete the electrical connection function. It is generally composed of a contact pair of an anode contact and a cathode contact. The electrical connection is completed by the insertion of the female and male contacts.

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

The cathode contact is the jack. It is a key part of the contact pair. The elastic structure depends on the elastic deformation when the pin is inserted and generates elastic force to form close contact with the positive contact to complete the connection. There are many types of jack structures, such as cylindrical type (slotted and narrowed), tuning fork type, cantilever beam (longitudinal slot), folding type (longitudinal slot, "9" shape), box shape (square jack ) And double-sided thread spring jacks, etc.

â‘¡Insulator. Insulators are also commonly referred to as bases or mounting plates. Their function is to arrange the contacts in the required position and spacing, and to ensure the insulation between the contacts and between the contacts and the housing. Good insulation resistance, voltage resistance and ease of processing are the basic requirements for selecting insulating materials to process into insulators.

â‘¢ Shell. The shell is also called the shell (depending on the variety), which is the outer cover of the connector, which provides mechanical protection for the built-in insulating mounting plate and pins, and provides alignment when the plug and socket are mated, thereby fixing the connector to On the device.

â‘£Accessories. The accessories are divided into structural accessories and installation accessories. Structural accessories such as snap rings, positioning keys, positioning pins, guide pins, connecting rings, cable clamps, sealing rings and gaskets, etc. Install accessories such as screws, nuts, screws and spring coils. Most of the accessories have standard parts and universal parts.

(2) Product classification of connectors

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

According to the above division, coaxial connectors are circular, and printed circuit connectors are rectangular (historically, printed circuit connectors are indeed separated from rectangular connectors from a class), and currently popular The rectangular connector has a trapezoidal cross section and is approximately rectangular. The low frequency and high frequency are divided with 3MHz as the boundary, which is basically the same as the frequency division of radio waves.

4. 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. Insertion force is divided into insertion force and extraction force (the extraction force is also called separation force), the requirements of the two are different.

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

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

(2) Electrical performance

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

â‘  Contact resistance. High-quality electrical connectors should have low and stable contact resistance. The contact resistance of the connector varies from a few milliohms to tens of milliohms.

â‘¡ Insulation resistance. The indicators for measuring the insulation performance between electrical connectors and between contacts and housings are on the order of hundreds of megohms to thousands of megohms.

â‘¢ Dielectric strength. The electric strength is also called withstand voltage and dielectric withstand voltage, and it is the ability to characterize the rated test voltage between the contacts of the connector or between the contacts and the housing.

â‘£ Other electrical properties. Electromagnetic interference leakage attenuation is to evaluate the electromagnetic interference shielding effect of the connector. Electromagnetic interference leakage attenuation is to evaluate the electromagnetic interference shielding effect of the connector, generally tested in the frequency range of 100MHz "10GHz.

For RF coaxial connectors, there are 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, that is, a high-speed signal connector, has appeared. Accordingly, in terms of electrical performance, in addition to characteristic impedance, some new electrical indicators have also appeared , Such as crosstalk, transmission delay and time lag.

(3) Environmental performance

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

â‘ Temperature 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. When the connector is working, the current generates heat at the contact point, resulting in a temperature rise, so 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 will affect the insulation performance of the connector and rust the metal parts. The constant humidity and heat test conditions are relative humidity at 90% ”95% (according to product specifications, up to 98%), temperature at + 40 ± 20oC, test time is at least 96h according to product regulations. Alternating humidity and heat test is more severe.

â‘¢Salt spray resistance. When the connector is working in an environment containing moisture and salt, the surface treatment layer of its metal structural parts and contact parts may produce galvanic corrosion, which affects the physical and electrical properties of the connector. In order to evaluate the ability of electrical connectors to withstand this environment, a salt spray test is specified. It hangs the connector in a temperature-controlled test chamber, sprays it with compressed air of a specified concentration of sodium chloride solution to form a salt spray atmosphere, and its exposure time is specified by the product specification, at least 48h.

â‘£ Vibration and shock resistance. Vibration and shock resistance are important performances of electrical connectors. They are particularly important in special application environments such as aviation and aerospace, railways, and road transport. It is an important indicator for testing the mechanical structure of electrical connectors and the reliability of electrical contact reliability. . There are clear regulations in the relevant test methods. The peak acceleration, duration and shock pulse waveform and the time of electrical continuity interruption shall be specified in the impact test.

⑤Other environmental performance. According to the requirements of use, other environmental properties of electrical connectors include sealing (air leakage, liquid pressure), liquid impregnation (ability to resist specific liquids) and low air pressure.

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