In order to reduce crosstalk between lines, the spacing between lines should be large enough. When the spacing between the center of lines is not less than 3 times the width of lines, 70% of the electric fields will not interfere with each other, which is called the 3W rule. To achieve 98 percent of the fields that do not interfere with each other, use a spacing of 10W.
Since the electric field between the power layer and the stratum is variable, electromagnetic interference will radiate outward at the edge of the plate. It’s called the edge effect.

The solution is to shrink the power supply layer so that the electric field only conducts within the boundaries of the ground. With one H (the thickness of the medium between the power source and the ground) as the unit, 70% of the electric field can be confined to the edge of the formation receiving if it is shrunk by 20H. Shrinkage of 100H limits 98% of the electric field.

Rule 55:

PCB layer number selection rule, that is, clock frequency to 5MHz or pulse rise time is less than 5ns, PCB board must use multi-layer board, this is a general rule, sometimes out of consideration of cost and other factors, using double-layer board structure, in this case, it is best to take the PCB side as a complete ground plane layer.