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Basics of connectors
1 What is a connector?
A connector is a component that our electrical engineering technicians often contact. Its role is very simple: between the blocked or isolated circuits in the circuit, a bridge is established to communicate, so that the current flows and the circuit achieves the intended function. Connectors are an indispensable part of electronic equipment. If you observe the path of current flow, you will always find one or more connectors. The form and structure of connectors are ever-changing. With different application objects, frequency, power, application environment, etc., there are various types of connectors. For example, connectors for lighting on the pitch and connectors for hard drives and rocket-ignition connectors are very different. But no matter what kind of connector, it is necessary to ensure that the current flows smoothly, continuously and reliably. Generally speaking, the connector is not limited to the current. In today's rapid development of optoelectronic technology, the carrier of signal transmission in optical fiber systems is light. Glass and plastic replace the wires in ordinary circuits, but optical signals Connectors are also used in the pathway, and they serve the same purpose as circuit connectors.
2 Why use a connector?
Imagine what would happen without a connector? At this time, the circuits should be permanently connected with continuous conductors. For example, if the electronic device is to be connected to the power supply, the two ends of the connecting wire must be fixed to the electronic device and the power supply by some method (such as welding). As a result, there are many inconveniences both in production and use. Take car batteries as an example. Assuming that the battery cable is fixedly welded to the battery, the car manufacturer increases the workload for installing the battery, increasing production time and cost. When the battery is damaged and needs to be replaced, the car must be sent to a repair station, the old one is removed by desoldering, and the new one is welded. Therefore, a larger labor cost is required. With the connector, you can save yourself a lot of trouble. Buy a new battery from the store, disconnect the connector, remove the old battery, install the new battery, and reconnect the connector. This simple example illustrates the benefits of connectors. It makes the design and production process more convenient and flexible, and reduces production and maintenance costs.
Benefits of connectors
Improve the production process Connectors simplify the assembly process of electronic products and also simplify the mass production process;
Easy to repair If an electronic component fails, the failed component can be quickly replaced when a connector is installed;
Easy to upgrade As technology advances, components can be updated when connectors are installed, replacing old ones with new, more complete components to increase design flexibility. The use of connectors gives engineers greater flexibility when designing and integrating new products, and when composing systems with components.
3 Classification of connectors
The classification of connectors has been confusing for many years, and each manufacturer has its own classification method and standard. In 1989, with the support of the National Electronic Distributors Association (NEDA, the abbreviation of National Electronic Distributors Association, which is an industrial education organization), several major manufacturers of connectors gathered together to develop a connector classification standard. And terminology. Molex has participated in the development process. NEDA Standard This standard developed by NEDA is called Levels of Packaging. The summary is described in the following table:
0 IC chip or chip-to-package connector Please note that the first level is "0" level, not "1" level. This level does not actually involve connection. Level 0 is an integrated circuit chip. Molex does not produce IC chips. But produce sockets that connect chips to circuit boards.
1 IC component or connector to (circuit) board When the IC chip is installed in the socket of the circuit board, it is a level 1 connection.
2 (printed) circuit board (PCB) to (printed) circuit board connector Level 2 connector is used for connection between printed circuit boards. .
3 Wire to circuit board or sub-assembly to sub-assembly connector A 3-level connector connects a printed circuit board and a sub-assembly, or connects two sub-assemblies. Sub-assembly is an integral part of electronic products. According to Molex's custom, Level 3 also includes some wire-to-wire connectors.
4 Chassis-to-chassis or input / output connector Level 4 connectors provide power or signal connections. A general rule of thumb is to use a level 4 connector when the connection involves audio or video signals, or when connecting to a network and a computer.
Regarding the above connector levels, the following points need to be noted:
■ Some connectors can be used in more than one grade. For example, the QF50 and MX50 3 grade connectors can be used in 2 or 4 grades. Another example is Molex I / O plugs and sockets, which can be used for wire-to-board or board-to-board connections.
■ In actual work, the connector is rarely mentioned according to the above level, but it is discussed according to the appearance and connection of the connector, such as board-to-board and wire-to-wire. Levels are used to learn and classify connectors
Basics of connectors
Basic structure of the connector
The basic structural parts of the connector are ① contact parts; ② insulators; ③ shells (depending on the variety); ④ accessories.
1. Contacts (contacts) are the core parts of the connector to complete the electrical connection function. The contact pair is generally composed of a positive contact and a negative contact, and the electrical connection is completed by the mating of the female and male contacts.
The male contact is a rigid part and its shape is cylindrical (round pin), square cylinder (square pin) or flat (pin). The male contact is generally made of brass or phosphor bronze.
The female contact is the key part of the contact pair. It relies on the elastic structure to elastically deform when mating with the pin to generate elastic force to form close contact with the male contact to complete the connection. There are many types of jacks, including cylindrical (slotted, narrowed), tuning fork, cantilevered (longitudinal slotted), folded (longitudinal slotted, 9-shaped), and box-shaped (square socket) And hyperboloid wire spring jacks.
2. Insulators Insulators are often called bases or inserts. Their 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, voltage resistance and easy processability are the basic requirements for selecting insulating materials for processing into insulators.
3． The shell, also called the shell, is the outer cover of the connector. It provides mechanical protection for the built-in insulation mounting plate and pins, and provides the alignment of the plug and socket when mating, thereby securing the connector to the device.
4． Accessories The accessories are divided into structural accessories and installation accessories. Structural accessories such as collars, positioning keys, positioning pins, guide pins, coupling rings, cable clamps, seals, gaskets, etc. Installation accessories such as screws, nuts, screws, spring coils, etc. Most of the accessories are standard parts and universal parts.
Basic performance of connectors
The basic performance of connectors can be divided into three categories: mechanical performance, electrical performance and environmental performance.
1. Mechanical properties: In terms of connection function, the insertion force is an important mechanical property. Insertion and extraction force is divided into insertion force and extraction force (extraction force is also called separation force), the requirements of the two are different. In the relevant standards, there are provisions for maximum insertion force and minimum separation force, which indicates that from the perspective of use, the insertion force is small (thus a structure with a low insertion force LIF and a non-insertion force ZIF), and if the separation force is too small, It will affect the reliability of the contact.
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 a specified insertion and removal cycle.
The insertion force and mechanical life of the connector are related to the contact structure (positive pressure), the quality of the plating at the contact part (coefficient of sliding friction), 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.
① Contact resistance A high-quality electrical connector should have a low and stable contact resistance. The contact resistance of a connector ranges from a few milliohms to tens of milliohms.
② Insulation resistance The index for measuring the insulation performance between the contacts of the electrical connector and between the contacts and the housing, which ranges from hundreds of megohms to thousands of megohms.
③ Electric strength, or withstand voltage, dielectric withstand voltage is the ability to withstand the rated test voltage between the contacts of the connector or between the contact and the housing.
④ Other electrical properties The electromagnetic interference leakage attenuation is used to evaluate the electromagnetic interference shielding effect of the connector. The electromagnetic interference leakage attenuation is used to evaluate the electromagnetic interference shielding effect of the connector. It is generally tested in the frequency range of 100MHz ~ 10GHz.
For RF coaxial connectors, there are also electrical specifications such as characteristic impedance, insertion loss, reflection coefficient, and voltage standing wave ratio (VSWR).
Due to the development of digital technology, in order to connect and transmit high-speed digital pulse signals, a new type of connector, namely a high-speed signal connector, has appeared. Correspondingly, in terms of electrical performance, in addition to characteristic impedance, some new electrical indicators have appeared , Such as crosstalk, delay, skew, etc.
3． Environmental performance
Common environmental properties include temperature, humidity, salt spray, vibration, and shock.
① Temperature resistance At present, the maximum working temperature of the connector is 200 ° C (except for a few high-temperature special connectors), and the minimum temperature is -65 ° C. As the connector works, the current generates heat at the contact point and causes a temperature rise, so it is generally considered that the operating temperature should be equal to the sum of the ambient temperature and the temperature rise of the contact. In some specifications, the maximum temperature rise allowed by the connector at the rated operating current is clearly specified.
② Resistance to moisture The penetration of moisture will affect the insulation performance of the connector and rust metal parts. The constant humidity and heat test conditions are 90% ~ 95% relative humidity (up to 98% according to product specifications), temperature + 40 ± 20 ° C, and the test time is at least 96 hours according to product regulations. Alternating damp heat tests are more severe.
③ Salt spray resistance When the connector works in an environment containing moisture and salt, the metal structure and contact surface treatment layer may cause galvanic corrosion, which affects the physical and electrical properties of the connector. To evaluate the electrical connector's ability to withstand this environment, a salt spray test is specified. It suspends the connector in a temperature-controlled test chamber and sprays compressed air with a sodium chloride solution of a specified concentration to form a salt mist atmosphere. The exposure time is specified by the product specification, at least 48 hours.
④ Vibration and shock Vibration and shock resistance are important properties of electrical connectors, and are particularly important in special application environments such as aviation and aerospace, railway and road transportation. It is a test of the mechanical structure of electrical connectors and the reliability of electrical contact Important indicators of sexuality. There are clear regulations in the relevant test methods.
The impact test shall specify the peak acceleration, duration and impact pulse waveform, and the time for electrical continuity interruption.
⑤ Other environmental properties According to the requirements of use, other environmental properties of the electrical connector include tightness (air leakage, liquid pressure), liquid impregnation (resistance to specific liquids), and low air pressure.
Classification and structure of connectors
As the structure of connectors becomes more and more diversified, new structures and application fields continue to appear. Attempting to use a fixed model to solve the classification and naming problems has become difficult to adapt. Nevertheless, some basic classifications are still valid.
1. Interconnection levels According to the functions of internal and external connections of electronic equipment, interconnection can be divided into five levels.
① Internal connection of chip package
② IC package pins and PCB connection. Typical connector IC socket.
③ The connection of printed circuit with wires or printed boards. A typical connector is a printed circuit connector.
④ The connection between the bottom plate and the bottom plate. A typical connector is a cabinet connector.
⑤ Device-to-device connection. Typical products are circular connectors.
There is some overlap in levels ③ and ④. Among the five-level connectors, the products with the highest market value are products at the third and third levels, and the products with the fastest growth are products at the third level.
2. Level of connector specifications. According to the classification of the International Electrotechnical Commission (IEC), connectors are electromechanical components for electronic equipment, and their specification levels are:
Family (family) example: connector
Sub-family example: circular connector
Type example: YB type circular connector
Example of style: YB3470
3． In China's industry management, connectors, switches, and keyboards are collectively referred to as electrical connector components, while electrical connector components and relays are collectively referred to as electromechanical components.
4． Product category of the connector. Although the classification of connector product types is somewhat confusing, technically, there are only two basic divisions of connector product categories:
① Structure according to shape: round and rectangular (cross section)
② By working frequency: 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. The rectangular connector has a trapezoidal cross section and is approximately rectangular. The division of low frequency and high frequency with radio frequency is also basically consistent with 3MHz as the boundary.
As for other uses, installation methods, special structures, special properties, etc., they can be divided into many different types, and often appear in publications and manufacturers' promotional materials, but generally only to highlight a certain feature and application, the basic classification is still It does not exceed the above-mentioned division principle.
Taking into account the technical development and actual situation of connectors, from its generality and related technical standards, connectors can be divided into the following categories (divided into categories):
① low-frequency circular connector; ② rectangular connector; ③ printed circuit connector; ④ radio frequency connector; ⑤ optical fiber connector.
5. Connector model designation. The connector model designation is the basis for customer procurement and manufacturer organization. In the connector industry at home and abroad, there are two ideas for product model naming: one is to use letter codes and numbers to try to reflect the product's