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Shielding method in high-speed PCB design
Posted: 06:23 PM March 21, 2018 Updated: 06:23 PM March 21, 2018

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 data twisted pair can rely on its own twisting to resist external interference and crosstalk between pairs at low frequencies, but only at high frequencies (especially when the frequency exceeds 250MHz) The twisted pair cannot achieve the purpose of anti-interference, and only the shield can resist external interference.

The cable shield acts like a Faraday shield. Interference signals enter the shield but do not reach the conductor. Therefore, data transmission can operate without failure. Because shielded cables have lower radiation emissions than unshielded cables, network transmissions are prevented from being intercepted. Shielded networks (shielded cables and components) can significantly reduce the level of electromagnetic energy radiation that can be intercepted by entering the surrounding environment.

Shielding interference fields of different interference fields mainly include electromagnetic interference and radio frequency interference. Electromagnetic interference (EMI) is mainly caused by low-frequency interference. 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 transmission, radar and other wireless communications are the usual source of radio frequency interference. For the resistance to electromagnetic interference, selecting the braided shield is the most effective because it has a lower critical resistance; for radio frequency interference, the foil layer shield is most effective because the braided shield relies on the change of wavelength, and the resulting gap makes the high frequency signal free In and out of the conductor; and for high and low frequency mixing of the interference field, we must use a wide-band coverage of the foil layer plus woven mesh combination of shielding. In general, the higher the mesh shielding coverage, the better the shielding effect.

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