PCB Technical - Shielding method of circuit board

The transmission rate of high-speed PCB design and wiring systems is steadily accelerating, but it also brings a certain anti-interference vulnerability. This is because the higher the frequency of transmission of information, the increase in signal sensitivity, and their energy is getting weaker and weaker. At this time, the wiring system is more susceptible to interference.

Interference is everywhere. Cables and equipment will interfere with other components or be seriously interfered by other sources of interference, such as: computer screens, mobile phones, motors, radio broadcasting equipment, data transmission and power cables, etc. In addition, potential eavesdroppers, cybercrimes and hackers are increasing because their interception of UTP cable information transmission will cause huge damage and loss.

Especially when using high-speed data networks, the time required to intercept a large amount of information is significantly lower than the time required to intercept low-speed data transmission. The twisted pair in the data twisted pair can rely on its own twisting to resist external interference and crosstalk between pairs at low frequencies, but at high frequencies (especially when the frequency exceeds 250MHz), only rely on Wire pair twisting can no longer achieve the purpose of anti-interference, and only shielding can resist external interference.

Shielding selection of different interference fields There are two main types of interference fields: electromagnetic interference and radio frequency interference. Electromagnetic interference (EMI) is mainly low-frequency interference. Motors, fluorescent lights, and power lines are common sources of electromagnetic interference. Radio frequency interference (RFI) refers to radio frequency interference, mainly high frequency interference. Radio, television broadcasting, radar and other wireless communications are common sources of radio frequency interference.

For resisting electromagnetic interference, the choice of braided shield is the most effective because it has a lower critical resistance; for radio frequency interference, the foil shield is the most effective, because the braided shield depends on the change of wavelength, and the gap it produces makes high-frequency signals free In and out of the conductor; and for the mixed interference field of high and low frequency, the combined shielding method of foil layer and woven net with broadband coverage function should be adopted. Generally, the higher the mesh shielding coverage, the better the shielding effect.

The function of the cable shield is like a Faraday shield. Interference signals will enter the shield but not the conductor. Therefore, the data transmission can run without failure. Since shielded cables have lower radiation emissions than unshielded cables, network transmission is prevented from being intercepted. The shielded network (shielded cables and components) can significantly reduce the level of electromagnetic energy that may be intercepted when entering the surrounding environment.