In any power supply design, the physical design of the PCB board is the last link, and its design method determines the electromagnetic interference and power supply stability, let's analyze these links specifically:
First, from the schematic to PCB design process to establish component parameters -> Input principle netsheet -> Design parameter setting -> Manual layout -> Manual wiring -> Verify the design -> review CAM output.
The spacing of adjacent wires must meet the electrical safety requirements, and in order to facilitate operation and production, the spacing should also be as wide as possible. The minimum spacing should at least be suitable for the voltage to withstand, when the wiring density is low, the spacing of the signal line can be appropriately increased, and the signal line with a high and low level disparity should be as short as possible and increase the spacing, under normal circumstances, the line spacing is set to 8mil.
The distance between the inner hole edge of the pad and the edge of the printed board should be greater than 1mm, which can avoid defects of the pad during processing. When the line connected with the pad is thin, the connection between the pad and the wire should be designed as a drop shape, which has the advantage that the pad is not easy to peel, but the wire and the pad are not easy to disconnect.
Practice has proved that even if the circuit schematic design is correct and the printed circuit board is improperly designed, it will adversely affect the reliability of electronic equipment. For example, if the two thin parallel lines of the printed board are close together, the delay of the signal waveform will be formed, and the reflected noise will be formed at the end of the transmission line. Due to the interference caused by the inconsiderate power supply and ground wire, the performance of the product will be reduced, therefore, when designing the printed circuit board, attention should be paid to the correct method.
Fourth, the wiring switching power supply contains a high frequency signal, any printed line on the PCB can play the role of antenna, the length and width of the printed line will affect its impedance and inductive reactance, thus affecting the frequency response. Even printed wires that pass through the DC signal can couple from adjacent printed wires to the RF signal and cause circuit problems (or even radiate interference signals again).
After the wiring design is completed, it is necessary to carefully check whether the wiring design meets the rules formulated by the designer, and it is also necessary to confirm whether the rules formulated meet the needs of the printed board production process, generally check whether the distance between the line and the line, the line and the component pad, the line and the through hole, the component pad and the through hole is reasonable, and whether the production requirements are met. Whether the width of the power cord and ground wire is appropriate, and whether there is a place in the PCB where the ground wire can be widened. Note: Some errors can be ignored, for example, some connectors have part of the Outline outside the board frame, and errors will be made when checking the spacing; In addition, after each modification of the wiring and through the hole, the copper should be re-coated once.
6. Review basis “ PCB checklist ” The content includes design rules, layer definition, line width, spacing, pad, and hole setting, and also focuses on reviewing the rationality of device layout, the routing of power supply and ground network, the routing and shielding of high-speed clock network, and the placement and connection of decoupling capacitors.
