1 Basic concepts of connectors
The basic performance of the connector can be divided into three parts, namely mechanical energy, electrical performance and environmental adaptability. There are two requirements for mechanical properties:
One is about the insertion force between the two contacts of the connector. We hope that the insertion force is relatively small and the separation force is appropriate. The second is about the mechanical life of the connector, which is the durability of the connector. The electrical performance consists of four parts, one is the contact resistance of the connector, the contact resistance should be small, it can be as good as tens of milliohms; the second is the insulation resistance, we hope it is very large, can reach hundreds of megohms or even gigabytes Europe; the third is the electric strength, which refers to the ability of the rated test voltage that can withstand between the connectors, the contacts, or the contacts and the housing; the fourth is the general electromagnetic performance, including electromagnetic interference The attenuation caused, and the ability to shield against electromagnetic interference. Environmental capabilities include three aspects: one is temperature resistance, according to the environment used by the connector, the actual temperature resistance range is different; the second is humidity resistance, which needs to reach 90% or higher; the third is salt spray resistance Salt spray can degrade the connector, or the surface is corroded; Fourth, the connector must be resistant to shock and vibration, because in some special environments, such as aerospace, railway transportation, road transportation, etc., the impact and vibration of electrical appliances Is very strong.
The development of connectors has the following characteristics:
1. Development in the direction of miniaturization, high density and high speed transmission;
2. Development towards high-performance and high-frequency technology;
3. The demand market for high voltage and high current connectors is also great;
4. The connector is also developing in the direction of anti-interference technology, modular technology and lead-free technology.
Table 1 lists typical high-speed connector models. In the case where the speed of the traditional parallel synchronous digital signal is about to reach its limit, the high-speed serial method is a good solution. This makes low-voltage differential signaling (LVDS) the primary next-generation high-speed signal level standard. The selection of high-speed connectors has also become the main problem to be solved for high-speed signal interconnection.
Several key technologies used in the development of high-speed connectors include:
1. Differential signal, noise-free signal and ground layer technology used to reduce crosstalk;
2. In order to adjust the lead of the connector, the delay difference caused by the unequal physical distance between the input and output of the connector can be changed;
3. In order to obtain the maximum transmission efficiency, the special impedance value of the connector should match the characteristic impedance of the transmission circuit.
2 Application of connectors in wired systems
Figure 1 shows a PSTN network switch, which consists of 7 parts. In addition to the difference in chassis size, the bottom of the chassis is a rack management module, which includes the management module, transmission backplane and transmission module. At the front are the daughter board, carrier board, power board, and air cooling system, fan support board. In the exchange, its main carrier board is the transmission of telephone information and the connection of input / output. The input and output systems consist of only a few computer boards and signaling control boards.
Any network needs connectivity in order to combine a single device into a network system. In today's networks, interconnected devices ("connectors") play an important role: first, they can electrically connect individual devices to form a larger network system; on the other hand, standardized interconnections are now used to make different companies make The devices can be connected to each other to work together, thereby forming a network in a certain block to meet the needs of businesses or communities.
Therefore, in the wired communication system, the role of the connector has three main aspects: first, it can achieve electrical connection between the circuit board and a single electrical component in a single device; second, if standardized interconnection is adopted, different companies The manufactured equipment is connected to work together to form a network in a certain block to meet the needs of business or community; third, by design to achieve reliable functions to withstand the known working environment and equipment eye period Work intensity.
For the connector requirements of the wired communication system, the following aspects should be considered in the design:
· Gold-plated contact interface to ensure higher wear resistance and good electrical characteristics;
· Redundant contact interface guarantees high reliability;
· Optional airtight connection or PCB welding;
· The external features of the shell should be easy to guide and guide when inserted;
· Use different pin heights to ensure the signal and ground connection sequence;
· Special terminals are needed for high-power power supply, which is different from the signal contact terminals;
· To ensure EMI characteristics and chassis grounding.
Figure 2 shows the design of a backplane connector in a typical connection system. It can provide three terminal lengths, that is, the lengths of the ground terminal, signal 1 terminal, and signal 2 terminal are different. This is to ensure that when the socket and the pin are connected to each other, if the connection is reversed, they cannot be inserted. The second part is the middle part. It is used for installation and maintenance. During the insertion of the entire pin board, it can be used for guidance, and even the correct coding and polarity can be guaranteed. The outer wall is used to protect the terminal and the guide of the connector. This terminal is the pin part and uses a flexible pin. As can be seen from the right half of the figure, after the housing is removed, the contact surface is more clearly shown. It uses a double-column redundant contact surface design, which can greatly improve the reliability of contact.
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