The circuit board, the full name of the printed circuit board, is a bridge between high-tech signal communication, including the industrial board connecting the switch and the machinery, in the production process of the circuit board, PCB manufacturers always play a circle of holes and copper tape around the industrial board or RF board, and even some RF board will be metallized around the four edges of the board. Many small partners do not understand why to do so, is it engineers show technology, do useless work?
pcb circuit board
No, it's not. There's a purpose to it. Nowadays, with the improvement of system speed, not only the timing and signal integrity problems of high-speed signals are prominent, but also the EMC problems caused by electromagnetic interference and power integrity caused by 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 interference within the system, reduce the anti-interference ability of the system, but also produce strong electromagnetic radiation to the outer space, causing the electromagnetic radiation emission of the system to seriously exceed the EMC standard, so that the products of the circuit board manufacturers can not pass the EMC standard certification. The edge radiation of multilayer PCB is a common source of electromagnetic radiation. Edge radiation occurs when an unexpected current reaches the edge of the ground layer and the power layer, with grounding and power supply noise in the form of inadequate power supply bypass. The cylindrical radiating magnetic field generated by the inductive hole radiates between the layers of the board and finally meets at the edge of the board. The return current of the strip line carrying the high frequency signal is too close to the edge of the board. In order to prevent these situations, a ring of ground holes is made around the PCB board with 1/20 wavelength hole spacing to form a ground hole shield to prevent external radiation of TME waves.
pcb board
For the microwave circuit board, its wavelength is further reduced, and due to the PCB production process now, the spacing between holes and holes can not be made very small, at this time has 1/20 wavelength spacing in the PCB around the way to play shielded holes for the microwave board is not obvious, then you need to use the PCB version of metalization edge process, the entire board edge surrounded by metal, Thus, the microwave signal can not radiate out from the PCB board edge, of course, the use of plate edge metallization process, will also lead to PCB manufacturing costs increase a lot. For RF microwave boards, some sensitive circuits, and circuits with strong radiation sources can be designed to weld a shielding cavity on the PCB, and the PCB board should be added "through the hole shielding wall" in the design, that is, the PCB and the shielding cavity wall close to the part of the ground through the hole. This creates a relatively isolated area. After confirming that it is correct, it can be sent to the multi-layer circuit board manufacturer for production.
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