High-speed PCB to solve. Here are nine rules:

Rule 1: High-speed signal routing shielding rule

In high-speed PCB design, key high-speed signal lines such as clocks need to be shielded. If they are not shielded or only partially shielded, EMI leakage will be caused. It is recommended that shielded cables be drilled for grounding every 1000mil.

Rule 2: closed-loop routing rules for high-speed signals

Closed-loop routing rules for high-speed signals

What are the rules of EMI for high-speed PCB design

Closed-loop routing rules for high-speed signals

Due to the increasing density of PCB board, many PCB LAYOUT engineers are prone to make a mistake in the process of wiring. In other words, high-speed signal network such as clock signal generates closed-loop results when multi-layer PCB wiring. Such closed-loop results will generate ring antenna and increase EMI radiation intensity.

Rule 3: open-loop routing rules for high-speed signals

Open-loop routing rules for high-speed signals

What are the rules of EMI for high-speed PCB design

Open-loop routing rules for high-speed signals

Rule 2 mentioned that the closed-loop of high-speed signals will cause EMI radiation, while the open-loop will also cause EMI radiation.

In high-speed signal network, such as clock signal, once the result of open loop is generated in the routing of multi-layer PCB, linear antenna will be generated and EMI radiation intensity will be increased.

Rule 4: characteristic impedance continuity rule for high-speed signals

Characteristic impedance continuity rule for high-speed signals

What are the rules of EMI for high-speed PCB design

Characteristic impedance continuity rule for high-speed signals

For high-speed signals, the continuity of characteristic impedance must be ensured when switching between layers; otherwise, EMI radiation will be increased. That is, the wiring width of the same layer must be continuous, and the wiring impedance of different layers must be continuous.

Rule 5: routing direction rules for high-speed PCB design

Characteristic impedance continuity rule for high-speed signals

What are the rules of EMI for high-speed PCB design

The cables between two adjacent layers must be routed vertically. Otherwise, crosstalk may occur and EMI radiation may increase. In short, adjacent wiring layers follow a horizontal, horizontal and vertical wiring direction, and vertical wiring can suppress crosstalk between lines.

Rule 6: Topology rules in high-speed PCB design

What are the rules of EMI for high-speed PCB design

Characteristic impedance continuity rule for high-speed signals

In high-speed PCB design, the control of circuit board characteristic impedance and the design of topological structure under multi-load directly determine the success or failure of the product.

The Daisy chain topology is shown in the figure, which is generally beneficial for a few Mhz. It is recommended to use the star symmetric structure at the back end in high-speed PCB design.

Rule 7: Resonance rule of line length

Resonance rule of line length

What are the rules of EMI for high-speed PCB design

Resonance rule of line length

Check whether the length of the signal line and the frequency of the signal constitute resonance, namely when the wiring length is the integer times of signal wavelength 1/4, this wiring will produce resonance, and resonance will radiate electromagnetic waves, produce interference.

Rule 8: Backflow path rule

Backflow path rule

What are the rules of EMI for high-speed PCB design

Backflow path rule

All high-speed signals must have a good backflow path. Minimize the backflow path of high-speed signals such as clocks. Otherwise the radiation will greatly increase, and the amount of radiation is proportional to the area surrounded by the signal path and the backflow path.

Rule 9: Device decoupling capacitor placement rules

Rules for placing decoupling capacitors of devices

What are the rules of EMI for high-speed PCB design

Rules for placing decoupling capacitors of devices

The location of the decoupling capacitor is very important. Improper placement can not achieve the effect of decoupling. The principle is: close to the power supply pin, and the capacitor’s power supply wiring and ground surrounded by the smallest area.