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PCB design to avoid electromagnetic interference and stabilize common supply voltage and current
PCB, or Printed Circuit Board, is a fundamental electronic component that serves as a platform for mounting and connecting electronic parts. It is commonly referred to as a "printed" circuit board because it is manufactured using an electronic printing process. The PCB provides mechanical support and electrical connectivity for various components, making it essential in almost all modern electronic devices.
In any power supply design, the physical layout of the PCB is the final stage. The design approach directly influences electromagnetic interference (EMI) and the stability of the power supply. Below are key considerations during the design process:
First, the transition from a schematic diagram to a PCB layout involves several steps: setting up component parameters, importing the schematic netlist, defining design rules, manually placing components, routing the connections, verifying the design, conducting a review, and generating CAM output.
Second, when setting the spacing between adjacent conductors, it's crucial to meet both electrical safety standards and manufacturing requirements. The minimum spacing should be sufficient to withstand the operating voltage. When the density is low, signal lines can be spaced further apart. High and low-level signals should be kept as short as possible, with increased spacing between them. Typically, a trace spacing of 8 mils is recommended. The distance between the pad edge and the board edge should be more than 1mm to avoid defects during fabrication. If the traces connected to the pads are thin, a droplet-shaped connection is preferred, which helps prevent the pads from peeling off and reduces the risk of disconnection between the trace and the pad.
Third, component placement plays a vital role in the reliability of the final product. Even if the schematic is correct, poor PCB design can lead to performance issues. For example, closely spaced thin parallel lines may cause signal delays and reflection noise at the end of transmission lines. Mismatched power and ground lines can introduce noise, degrading the system's performance. Therefore, careful attention must be paid to proper design techniques.
Fourth, in switching power supplies, high-frequency signals are present on the PCB. Any trace can act as an antenna, affecting impedance and inductance, which in turn impacts frequency response. Even DC traces can couple with RF signals from nearby traces, leading to unwanted interference or radiated emissions.
Fifth, after completing the wiring, it’s important to verify that all design rules are followed and that the layout meets the manufacturing specifications. This includes checking the distances between lines and components, lines and vias, pads and vias, and vias and vias. The width of power and ground traces should be adequate, and areas where the ground plane can be widened should be considered. Minor errors, such as connectors placed outside the board outline, can cause problems during spacing checks. Additionally, whenever traces or vias are modified, the copper layers should be re-routed accordingly.
Sixth, a thorough review based on a PCB checklist is essential. This includes checking design rules, layer definitions, line widths, spacing, pad and via settings, as well as evaluating the layout of components, power and ground networks, high-speed clock routing, shielding, and the placement and connection of decoupling capacitors.
By following these guidelines, designers can ensure a reliable, efficient, and manufacturable PCB layout.