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Electronic Design

Electronic Design

Electronic Design

Electronic Design

Summary and cause analysis of high-speed PCB design rules

1. The pcb clock frequency exceeds 5MHZ or the signal rise time is less than 5ns, generally a multi-layer board design is required.

Reason: The area of signal loop can be well controlled by adopting multi-layer board design.

2. For multilayer boards, the key wiring layer (the layer where the clock line, bus, interface signal line, radio frequency line, reset signal line, chip select signal line and various control signal lines are located) should be adjacent to the complete ground plane, preferably Between two ground planes.

Reason: The key signal lines are generally strong radiation or extremely sensitive signal lines. Wiring close to the ground plane can reduce the signal loop area, reduce the radiation intensity or improve the anti-interference ability. `

3. For single-layer boards, both sides of the key signal lines should be covered with ground.

Reason: The key signal is covered with ground on both sides, on the one hand, it can reduce the area of the signal loop, and on the other hand, it can prevent the crosstalk between the signal line and other signal lines.

4. For double-layer boards, a large area of ground is laid on the projection plane of the key signal lines, or the same as the single-sided board, the ground is perforated.

Reason: the same as the key signal of the multilayer board is close to the ground plane.

5. In a multilayer board, the power plane should be retracted by 5H-20H relative to its adjacent ground plane (H is the distance between the power supply and the ground plane).

pcb board

.Reason: The indentation of the power plane relative to its return ground plane can effectively suppress the edge radiation problem.

6. The projection plane of the wiring layer should be in the area of the reflow plane layer.

Reason: If the wiring layer is not in the projection area of the reflow plane layer, it will cause edge radiation problems and increase the signal loop area, resulting in increased differential mode radiation.

7. In the multi-layer board, the TOP and BOTTOM layers of the single board should not have signal lines larger than 50MHZ as far as possible.

Reason: It is best to walk the high-frequency signal between the two plane layers to suppress its radiation to the space.

8. For a single board with a board-level operating frequency greater than 50MHz, if the second layer and the penultimate layer are wiring layers, the TOP and BOOTTOM layers should be covered with grounded copper foil.

Reason: It is best to walk the high-frequency signal between the two plane layers to suppress its radiation to the space.

9. In multi-layer boards, the main working power plane of the single board (the most widely used power plane) should be in close proximity to its ground plane.

Reason: The adjacent power plane and ground plane can effectively reduce the loop area of the power circuit.

10. In a single-layer board, there must be a ground wire next to and parallel to the power trace.

Reason: reduce the area of the power supply current loop.

11. In a double-layer board, there must be a ground wire next to and parallel to the power supply line.

Reason: reduce the area of the power supply current loop.

12. In the layered design, try to avoid the adjacent setting of the wiring layer. If it is unavoidable that the wiring layers are adjacent to each other, the layer spacing between the two wiring layers should be appropriately increased, and the layer spacing between the wiring layer and its signal circuit should be reduced.

Reason: Parallel signal traces on adjacent wiring layers can cause signal crosstalk.

13. Adjacent plane layers should avoid overlapping of their projection planes.

Reason: When the projections overlap, the coupling capacitance between the layers will cause the noise between the layers to couple with each other.

14. When designing the PCB layout, fully comply with the design principle of placing in a straight line along the signal flow direction, and try to avoid looping back and forth.

Reason: Avoid direct signal coupling and affect signal quality.

15. When multiple module circuits are placed on the same PCB, digital circuits and analog circuits, and high-speed and low-speed circuits should be laid out separately.

Reason: Avoid mutual interference between digital circuits, analog circuits, high-speed circuits, and low-speed circuits.

16. When there are high, medium, and low speed circuits on the circuit board at the same time, follow the high and medium speed circuits and stay away from the interface.

Reason: Avoid high-frequency circuit noise from radiating to the outside through the interface.

17. Energy storage and high-frequency filter capacitors should be placed near unit circuits or devices with large current changes (such as power supply modules: input and output terminals, fans and relays).

Reason: The existence of energy storage capacitors can reduce the loop area of large current loops.

18. The filter circuit of the power input port of the circuit board should be placed close to the interface.

Reason: to avoid re-coupling the line that has been filtered.

19. On the PCB, the filtering, protection and isolation components of the interface circuit should be placed close to the interface.

Reason: It can effectively achieve the effects of protection, filtering and isolation.

20. If there is both a filter and a protection circuit at the interface, the principle of first protection and then filtering should be followed.

Reason: The protection circuit is used to suppress external overvoltage and overcurrent. If the protection circuit is placed after the filter circuit, the filter circuit will be damaged by overvoltage and overcurrent.