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High Speed ​​PCB Design Rules Summary and Analysis (1)

Posted:05:18 PM May 29, 2018 writer: G

Reason: The use of multi-layer board design signal circuit area can be well controlled.

2. For multilayer boards, the key wiring layers (clock layer, bus, interface signal lines, RF lines, reset signal lines, chip select signal lines, and various control signal lines, etc.) should be adjacent to the complete ground plane. Between the two ground planes.

Reason: The critical signal lines are generally strong radiation or extremely sensitive signal lines. Close to the ground plane wiring can reduce the signal loop area, reduce its radiation intensity or improve the anti-jamming capability. `

3. For single-layer boards, both sides of the key signal line should be packaged.

Reasons: The package of signals on both sides of the key signal can, on the one hand, reduce the signal loop area and prevent crosstalk between the signal line and other signal lines.

4. For the double-layer board, there is a large area of floor covering on the projection plane of the key signal line, or the hole punching process is carried out in the same way as the single-sided board.

Reason: The key signal of the multi-layer board is close to the ground plane.

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

Reason: The in-plane shrinkage of the power plane relative to its reflow plane can effectively suppress edge radiation problems.

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

Reason: If the wiring layer is not in the projection area of the reflow plane layer, it will cause the edge radiation problem, and lead to the increase of the signal loop area, which will lead to the increase of differential mode radiation.

7. In multilayer boards, the TOP and BOTTOM layers of the board should have no signal lines greater than 50 MHz.

Reason: It is best to walk high-frequency signals between two plane layers to suppress their radiation to space.

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

Reason: It is best to walk high-frequency signals between two plane layers to suppress their radiation to space.

9. In multilayer boards, the main power supply plane of the board (the most widely used power plane) should be immediately adjacent to its ground plane.

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

10. In a single-layer board, the ground wire must be adjacent to and parallel to the power supply wiring.

Reason: Reduce the power supply current loop area.

11. In the double-layer board, the ground wire must be adjacent to and parallel to the power supply wiring.

Reason: Reduce the power supply current loop area.

12. In the layered design, try to avoid the adjacent layout of the wiring layer. If the wiring layers cannot be avoided, the spacing between the two wiring layers should be appropriately widened, and the spacing between the wiring layer and its signal circuit should be reduced.

Reason: Parallel signal traces on adjacent routing 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 causes the noise between the layers to couple.

14. When designing a PCB layout, the design principle of placing lines along the line of signal shall be fully observed to avoid 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, high-speed and low-speed circuits should be laid out separately.

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

16. When high-, medium-, and low-speed circuits exist on the circuit board at the same time, the high- and medium-speed circuits should be kept away from the interface.

Reason: Avoid high-frequency circuit noise radiated through the interface.

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

Reason: The presence of the energy storage capacitor can reduce the loop area of the large current loop.

18. Circuit board power input filter circuit should be placed near the interface.

Reason: Avoid re-coupling of lines that have been filtered.

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

Reason: The effect of protection, filtering, and isolation can be effectively achieved.

20. If the interface has both filtering and protection circuits, it should follow the principle of first protection after filtering.

Reason: The protection circuit is used for external overvoltage and overcurrent suppression. If the protection circuit is placed behind the filter circuit, the filter circuit will be damaged by overvoltage and overcurrent.

21. Layout to ensure that the filter circuit (filter), isolation and protection circuit input and output lines do not couple with each other.

Reason: When the input and output traces of the above circuit are coupled to each other, the filtering, isolation, or protection effects are impaired.

22. If the interface is designed to be “clean” on the board, the filtering and isolation devices shall be placed on the isolation band between “clean” and the work place.

Reason: Avoiding filtering or isolating devices coupled to each other through the plane layer weakens the effect.

23. On the "clean" side, no other device can be placed other than filtering and protection devices.

Reason: The purpose of the "clean" design is to ensure minimal radiation to the interface and to "cleanly" easily interfere with coupling from outside, so there should be no extraneous circuitry and devices on the "clean" side.

24. Strong radiation devices such as crystals, crystal oscillators, relays, switching power supplies, etc. are at least 1000 mils away from the single-board interface connector.

Reason: The interference will be directly radiated outwards or coupled to the outgoing cable to radiate outwards.

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