“20H” rule This rule defines the overlapping distance between the ground layer and the power layer in the PCB. In modern PCB design, the power supply needs to be laid near the ground wire, so as to ensure sufficient interlayer capacitance between them, and then Reduce power fluctuations on high-speed circuit boards. But the actual measurement will turn out to be complicated. Some time results standard name at 300MHz observance of 20H law can reduce electromagnetic radiation. However, high-frequency resonance will occur between the ground wire and the power supply layer. Their structure is similar to a waveguide, which will aggravate the high-frequency interference between the lines.