20H principle in PCB design
The adoption of 20H rule means to ensure that the edge of the power supply plane is at least 20 times the distance between the two planes than the edge of the 0V plane. This rule is often required to reduce side firing from the plane structure of 0V/ power supply (suppression of edge radiation effect).
However, the 20H rule will only provide significant results under certain conditions. These specific conditions include:
1. The rise/fall time of current fluctuations in the power bus is less than 1ns.
2. The power plane is on the internal of the PCB, and the upper and lower layers adjacent to it are 0V planes. The two 0V planes extend outward at least 20 times the distance between their respective planes from the power plane.
3. The power bus structure does not resonate at any frequency of concern.
4. The total derivative of the PCB is at least 8 layers or more.