How to do EMC design in PCB wiring?

As we all know, when designing PCB, if it’s just an ordinary board, just do a good job of precise design of mechanical dimensions. However, if high-frequency signals, load lines or long lines are used, these lines should be treated specially; otherwise, a series of signal interference problems, such as reflection and crosstalk between lines, may be caused. Therefore, when we are doing circuit design, especially high-speed PCB design, we must do a good job of imitating interference of line signals, and shielding measures are very necessary. Let’s talk about PCB wiring, and how to do EMC design.
1. Appropriate wire width
When selecting the wire width, it is usually determined by the minimum current value it bears to ensure the electrical performance and facilitate production. In order to reduce the electromagnetic interference impact caused by transient current on printed boards, it is necessary to control the line width in design. Transient interference is generally caused by the inductance of the wire, and its inductance is directly proportional to the length of the wire and inversely proportional to the line width. For signal lines with large transient currents, short and wide wires should be adopted. If the layout space allows, the grid-like layout structure should be adopted as much as possible.
2. Key points of component wiring
The wiring design of components mainly considers several aspects: first, the electrical performance; When wiring, we should try our best to put the devices close to the wiring together. The layout of high-speed lines should be as short as possible, and the power devices and small-signal devices should be laid out separately. Second, the placement position; Whether the design is beautiful and tidy, and whether it is convenient for functional testing, later interface and connection. In high-speed systems, the transmission delay of grounding and interconnection lines is also the first design factor that we need to consider. The transmission time of signal transmission line has a great influence on the overall system speed of the circuit. If ordinary interconnection lines are used in places where high-speed lines are used, the delay time will be increased and the system speed will be greatly reduced.
3. Wiring rules for high-frequency and high-speed signals
Generally, equal wiring can reduce the inductance between wires, but in order to suppress the crosstalk of PCB circuit wires, we should try our best to avoid long-distance equal wiring when designing wiring; When designing printed wires, sharp turns should be avoided, and even curves with certain radians should be designed as far as possible; For components with high current on the circuit, try to separate the ground wire to avoid noise interference, and set grounding between small signal or sensitive signal wires; The high-speed signal adopts differential signal wiring design, so that the two differential lines in the positive and negative pairs always keep the transmission lines coupled with each other, effectively reducing the electrical noise effect of the signal.