Circuit board, the full name of printed circuit board, is a bridge for signal communication between high-tech, among which there is an industrial control board that connects switches and machinery. A circle of vias and copper tapes are placed around the board, and even some RF boards will be metallized and wrapped around the board. Many small partners do not understand why they do this. Is it an engineer showing off technology and doing useless work?

　　In fact, it is not, it is naturally purposeful. Nowadays, with the improvement of system speed, not only the timing and signal integrity of high-speed signals are prominent, but also the EMC problems caused by electromagnetic interference and power integrity of high-speed digital signals in the system are also very prominent. The electromagnetic interference generated by high-speed digital signals will not only cause serious mutual interference inside the system and reduce the anti-interference ability of the system, but also generate strong electromagnetic radiation in the external space, causing the electromagnetic radiation emission of the system to seriously exceed the EMC standard, making the circuit The products of board manufacturers cannot pass the EMC standard certification. The edge radiation of the multilayer PCB is a relatively common source of electromagnetic radiation. Edge radiation occurs when unexpected currents reach the edges of the ground and power planes, with ground and power noise that manifests as: Insufficient power bypassing. The cylindrical radiated magnetic field generated by the inductive via radiates between the layers of the circuit board and eventually meets at the edge of the circuit board. Stripline return currents that carry high frequency signals are too close to the edge of the board. In order to prevent these situations from occurring, a circle of ground vias are punched around the PCB with a 1/20 wavelength hole spacing to form a ground via shield to prevent TME waves from radiating externally.

　　For microwave circuit boards, the wavelength is further reduced, and due to the current PCB production process, the spacing between holes cannot be made very small. At this time, the spacing of 1/20 wavelength is shielded by holes around the PCB. The effect of the microwave board is not very obvious. At this time, it is necessary to use the PCB version metallization wrapping process to surround the entire edge of the board with metal, so that the microwave signal cannot be radiated from the edge of the PCB board. Of course, the edge metallization package is used. The edge process will also lead to a lot of increase in the manufacturing cost of the PCB. For RF microwave boards, some sensitive circuits, and circuits with strong radiation sources can design a shielding cavity soldered on the PCB. The PCB circuit board should be designed with a "via-hole shielding wall", that is, on the PCB and shielding. The part where the cavity wall is close to the ground is added with a grounded via. This forms a relatively isolated area. After confirmation, it can be sent to the multi-layer circuit board manufacturer for production.

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