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How to deal with cross-partition and slotting in EMC design, many novices are not very clear about this. In order to help you solve this problem, the following editor will explain it in detail. People with this need can come and learn. I hope you can get something.

I. the formation of slotting in the process of PCB design.

The formation of slots in the PCB design process includes:

Slotting caused by power source or ground plane division; when there are many different power sources or ground on the PCB board, it is generally impossible to assign a complete plane to each power network and ground network, and the common practice is to divide the power supply or ground on one or more planes. Slots are formed between different divisions on the same plane.

The through holes are too dense to form slots (including pads and through holes); when the through holes pass through the stratum or power layer without electrical connection, some space needs to be left around the through holes for electrical isolation; but when the distance between the through holes is too close, the isolation rings will overlap to form slots.

2. The effect of slotting on the performance of PCB EMC.

Slotting will have a certain impact on the EMC performance of PCB board, which may be negative or positive. First of all, we need to understand the surface current distribution of high-speed signal and low-speed signal. At low speed, the current flows along the path with the lowest resistance. The following figure shows that when the low-speed current flows from A to B, the reflux signal returns from the ground plane to the source. At this time, the distribution of surface current is wide.

In the case of high speed, the effect of the inductor on the signal reflux path will exceed that of the resistance. The high-speed reflux signal will flow along the path with the lowest impedance. At this time, the distribution of the surface current is very narrow, and the reflux signal is concentrated in bundles below the signal line.

When there are incompatible circuits on the PCB board, it is necessary to "divide the ground", that is, to set the ground plane according to different power supply voltage, digital and analog signals, high and low speed signals, large current and small current signals. From the distribution of the reflux of the high-speed signal and the low-speed signal given above, it is easy to understand that the land separation can prevent the superposition of the reflux signal of the incompatible circuit and prevent the common ground line impedance coupling.

However, whether it is a high-speed signal or a low-speed signal, when the signal line crosses the slots in the power plane or ground plane, it will bring a lot of serious problems, including:

Increase the area of the current loop and increase the loop inductance, so that the output waveform is easy to oscillate.

For high-speed signal lines which need strict impedance control and run according to the strip model, the strip model will be destroyed because of the slotting in the upper plane or lower plane or the upper and lower plane, resulting in impedance discontinuity and serious signal integrity problems.

Increase the radiation emission to space and be vulnerable to the interference of space magnetic field

The high frequency voltage drop on the loop inductor forms the common mode radiation source, and the common mode radiation is generated through the external cable.

Increase the possibility of crosstalk with other circuits on the board.

Third, the treatment of slotting in PCB design

The treatment of slotting should follow the following principles:

For high-speed signal lines that require strict impedance control, the trajectory is strictly forbidden to cross split lines to avoid causing impedance discontinuity and serious signal integrity problems.

When there is an incompatible circuit on the PCB board, the land division should be carried out, but the land division should not cause the cross-split line of the high-speed signal line or the cross-split line of the low-speed signal line.

When cross-slotted alignment is inevitable, bridging should be carried out.

The connector (external) should not be placed on the stratum partition. If there is a large potential difference between point An and point B on the stratum, it is possible to produce common mode radiation through external cables.

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