In any power supply design, the physical design of the PCB board is the last link. The design method determines electromagnetic interference and power supply stability. Let’s analyze these links in detail.
1. From the schematic to the PCB design process to establish component parameters-“input principle netlist-“design parameter settings-“manual layout-“manual wiring-“verify design-“review-“CAM output.
2. Parameter setting: The distance between adjacent wires must be able to meet the electrical safety requirements, and in order to facilitate operation and production, the distance should be as wide as possible. The minimum spacing must be at least suitable for the voltage tolerated. When the wiring density is low, the spacing of the signal lines can be appropriately increased. For signal lines with a large gap between high and low levels, the spacing should be as short as possible and the spacing should be increased. Generally, Set the trace spacing to 8mil.
The distance between the edge of the inner hole of the pad and the edge of the printed board should be greater than 1mm, which can avoid the defects of the pad during processing. When the traces connected to the pads are thin, the connection between the pads and the traces should be designed into a drop shape. The advantage of this is that the pads are not easy to peel, but the traces and the pads are not easily disconnected.
3. The component layout practice has proved that even if the circuit schematic design is correct and the printed circuit board is not properly designed, it will have an adverse effect on the reliability of electronic equipment. For example, if the two thin parallel lines of the printed board are close together, it will cause a delay in the signal waveform and form reflected noise at the end of the transmission line. Interference caused by improper consideration of the power supply and ground will cause the product to suffer performance drops, so when designing the printed circuit board, you should pay attention to adopting the correct method.
4. Wiring the switching power supply contains high-frequency signals. Any printed line on the PCB can function as an antenna. The length and width of the printed line will affect its impedance and inductance, thereby affecting the frequency response. Even printed lines that pass DC signals can couple to radio frequency signals from adjacent printed lines and cause circuit problems or even radiate interfering signals again.
5. After the wiring design is completed, it is necessary to carefully check whether the wiring design conforms to the rules set by the designer. At the same time, it is also necessary to confirm whether the rules made meet the requirements 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, the through hole and the through hole is reasonable, and whether it meets the production requirements. Whether the width of the power line and the ground line are appropriate, and whether there is a place to widen the ground line in the PCB. Note: Some errors can be ignored. For example, a part of the outline of some connectors is placed outside the board frame, and errors will occur when checking the spacing. In addition, each time the wiring and vias are modified, the copper must be re-coated.
6. Review according to the “PCB checklist”. The content includes design rules, layer definitions, line widths, spacing, pads, and via settings, and also focus on reviewing the rationality of the device layout, the routing of power and ground networks, and high-speed routing and shielding of the clock network, the placement and connection of decoupling capacitors, etc.
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