Shielding method in high speed PCB design

- Mar 31, 2017-

High speed PCB design layout of the transmission rate of the system at the same time steadily accelerating has also brought some anti interference vulnerability, this is because the information transmission frequency is high, the increase of signal sensitivity, and their energy is more and more weak, the wiring system more vulnerable to interference.

Interference everywhere, cables and equipment will produce interference or other sources of interference interference to other components such as: computer screen, mobile phone, electric motor, radio relay equipment, data transmission and power cable etc.. In addition, the potential for eavesdropping, cyber crime and hackers continue to increase, because they will be caused by the interception of UTP cable information transmission will cause great damage and loss.

Especially in the use of high-speed data networks, the time needed to intercept large amounts of information is significantly less than the time needed to intercept low speed data transmission. The data in the twisted pair twisted pair at low frequency can be crosstalk on its own to resist external interference and stranded on the line between, but in the case of high frequency (especially in the frequency of more than 250MHz), on line to the stranded has been unable to achieve the purpose of anti-interference, only able to resist external interference shielding.

The cable shield acts like a Faraday shield, which interferes with the signal into the shield, but not into the conductor. Therefore, data transmission can be run without fault. Because the shielded cable has lower radiation emission than the non shielded cable, the network transmission is prevented. Shielding networks (shielded cables and components) can significantly reduce the level of electromagnetic energy radiated into the surrounding environment and may be intercepted.

There are two kinds of electromagnetic interference and radio frequency interference. Electromagnetic interference (EMI) is mainly low frequency interference, motors, fluorescent lamps and power lines are the usual electromagnetic interference sources. Radio frequency interference (RFI) is a kind of radio frequency interference. Radio, television, radar and other wireless communications are the common sources of radio frequency interference.

For resistance to electromagnetic interference, selection of braided shielding is most effective, because of its low critical resistance; for radio frequency interference, the most effective foil shield, because of changes in braided shielding depends on the wavelength of the gap, it generates the high-frequency signal can be freely conductor; while for high frequency hybrid interference field to using a combination of broadband shielding foil layer covering function with mesh. Usually, the higher the shielding coverage, the better the shielding effect.

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