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Shielding method in high speed PCB design

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Published by: Keyou September 30,2019
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  • PCB design
  • The transmission rate of the high-speed pcb design and routing system is steadily increasing, and it also brings some kind of anti-interference vulnerability. The higher the frequency of transmitting information, the greater the sensitivity of the signal, and the weaker their energy. The wiring system at this time is more susceptible to interference. Interference is ubiquitous, cables and equipment can interfere with other components or be severely interfered with by other sources of interference, such as computer screens, mobile phones, electric motors, radio equipment, data transmission and power cables. In addition, potential eavesdroppers, cybercrime and hackers are increasing because they can cause huge damage and loss in the interception of UTP cable information.

        Especially when using high-speed data networks, the time required to intercept large amounts of information is significantly lower than the time required to intercept low-speed data transmissions. The twisted pair in the data twisted pair can resist its external interference and crosstalk between the pairs at its low frequency, but at high frequencies (especially when the frequency exceeds 250MHz), Wire twisting has not been able to achieve the purpose of anti-interference, only shielding can resist external interference.

        The cable shield acts like a Faraday shield, and the interfering signal enters the shield but does not enter the conductor. Therefore, data transmission can run without problems. Since shielded cables have lower radiated emissions than unshielded cables, network transmissions are prevented from being intercepted. Shielded networks (shielded cables and components) can significantly reduce the level of electromagnetic radiation that can be intercepted into the surrounding environment.

     

                                         Shielding method in high speed PCB design

     

        The shielding field of different interference fields is mainly composed of electromagnetic interference and radio frequency interference. Electromagnetic interference (EMI) is mainly low frequency interference, and motors, fluorescent lamps, and power lines are common sources of electromagnetic interference. Radio Frequency Interference (RFI) refers to radio frequency interference, mainly high frequency interference. Radio, television, radar and other wireless communications are common sources of RF interference. For resisting electromagnetic interference, the choice of braided shield is most effective because it has a lower critical resistance; for radio frequency interference, the foil layer shielding is most effective, because the braided shield depends on the wavelength change, and the gap created by it makes the high frequency signal free. In and out of the conductor; for high-low frequency mixed interference field, a combination of foil layer and woven mesh with broadband coverage is used. In general, the higher the mesh shielding coverage, the better the shielding effect.

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