Rule 1: Shielding rules for high-speed signal routing
In the design of high-speed PCB boards, it is crucial to shield key high-speed signal lines and traces, such as clocks. Without proper shielding, or with only partial shielding, there can be EMI leakage. It is recommended to ground the shielded wires with holes at intervals of 1000mil.
Rule 2: Closed-loop routing rules for high-speed signals
With the increasing density of PCB boards, many LAYOUT engineers are prone to a common mistake in the routing process. When routing multi-layer PCB boards, high-speed signal networks, such as clock signals, can form closed loops, resulting in a loop antenna that increases the radiated intensity of EMI.
Rule 3: Open-loop routing rules for high-speed signals
While Rule 2 addresses the EMI radiation caused by closed loops in high-speed signals, it is important to note that open loops can also lead to EMI radiation. When routing multi-layer PCB boards, the formation of open loops for high-speed signal networks, like clock signals, can result in the generation of a linear antenna, leading to an increase in the radiation intensity of EMI.
Rule 4: Characteristic Impedance Continuity Rule for High-Speed Signals
For high-speed signals, it is crucial to ensure the continuity of characteristic impedance when switching between layers. Otherwise, there will be an increase in EMI radiation. This means that the width of the wiring on the same layer must be continuous, and the wiring impedance of different layers must also be continuous.
Rule 5: Wiring Direction Rules for High-Speed PCB Board Design
When designing high-speed PCB boards, the traces between two adjacent layers must follow the principle of vertical traces to avoid crosstalk between the lines and reduce EMI radiation. The adjacent wiring layers should follow the horizontal and vertical wiring directions, and the use of vertical wiring can help in suppressing crosstalk between the lines.
Rule 6: Topology Rules in High-Speed PCB Design
The control of the characteristic impedance of the circuit board and the design of the topology structure under multiple loads directly determine the success or failure of the product. A daisy-chain topology is generally beneficial for a few MHz, however, it is recommended to use the rear star symmetrical structure in high-speed PCB board designs.
Rule 7: Resonance Rule for Trace Length
It is important to check whether the length of the signal line and the frequency of the signal constitute resonance. Resonance occurs when the length of the wiring is an integer multiple of 1/4 of the signal wavelength, which leads to the generation of electromagnetic waves and interference.
Rule 8: Return Path Rules
All high-speed signals must have good return paths, especially for signals such as clocks. It is essential to keep the return paths of high-speed signals as small as possible to prevent an increase in radiation. The magnitude of the radiation is proportional to the area enclosed by the signal and return paths.
Rule 9: Placement Rules for Decoupling Capacitors of Devices
The placement of decoupling capacitors is crucial, as unreasonable placement will not achieve the desired decoupling effect. It is important to place the decoupling capacitors close to the power supply pin, and ensure that the area enclosed by the power supply trace and the ground wire of the capacitor is small on the PCB board.
In the design of high-speed PCB boards, it is crucial to shield key high-speed signal lines and traces, such as clocks. Without proper shielding, or with only partial shielding, there can be EMI leakage. It is recommended to ground the shielded wires with holes at intervals of 1000mil.
Rule 2: Closed-loop routing rules for high-speed signals
With the increasing density of PCB boards, many LAYOUT engineers are prone to a common mistake in the routing process. When routing multi-layer PCB boards, high-speed signal networks, such as clock signals, can form closed loops, resulting in a loop antenna that increases the radiated intensity of EMI.
Rule 3: Open-loop routing rules for high-speed signals
While Rule 2 addresses the EMI radiation caused by closed loops in high-speed signals, it is important to note that open loops can also lead to EMI radiation. When routing multi-layer PCB boards, the formation of open loops for high-speed signal networks, like clock signals, can result in the generation of a linear antenna, leading to an increase in the radiation intensity of EMI.
Rule 4: Characteristic Impedance Continuity Rule for High-Speed Signals
For high-speed signals, it is crucial to ensure the continuity of characteristic impedance when switching between layers. Otherwise, there will be an increase in EMI radiation. This means that the width of the wiring on the same layer must be continuous, and the wiring impedance of different layers must also be continuous.
Rule 5: Wiring Direction Rules for High-Speed PCB Board Design
When designing high-speed PCB boards, the traces between two adjacent layers must follow the principle of vertical traces to avoid crosstalk between the lines and reduce EMI radiation. The adjacent wiring layers should follow the horizontal and vertical wiring directions, and the use of vertical wiring can help in suppressing crosstalk between the lines.
Rule 6: Topology Rules in High-Speed PCB Design
The control of the characteristic impedance of the circuit board and the design of the topology structure under multiple loads directly determine the success or failure of the product. A daisy-chain topology is generally beneficial for a few MHz, however, it is recommended to use the rear star symmetrical structure in high-speed PCB board designs.
Rule 7: Resonance Rule for Trace Length
It is important to check whether the length of the signal line and the frequency of the signal constitute resonance. Resonance occurs when the length of the wiring is an integer multiple of 1/4 of the signal wavelength, which leads to the generation of electromagnetic waves and interference.
Rule 8: Return Path Rules
All high-speed signals must have good return paths, especially for signals such as clocks. It is essential to keep the return paths of high-speed signals as small as possible to prevent an increase in radiation. The magnitude of the radiation is proportional to the area enclosed by the signal and return paths.
Rule 9: Placement Rules for Decoupling Capacitors of Devices
The placement of decoupling capacitors is crucial, as unreasonable placement will not achieve the desired decoupling effect. It is important to place the decoupling capacitors close to the power supply pin, and ensure that the area enclosed by the power supply trace and the ground wire of the capacitor is small on the PCB board.
