The problem is that we are often taught that electronic circuits behave like water in pipes. But this is not the case, and if you design circuits based on this analogy, you are likely to encounter EMI issues.
In reality, if we want to contain EM fields, we need to select layers in the stackup in pairs, rather than as single layers.
This means that for each signal or power layer, there should be an adjacent solid Return Reference Plane (RRP), which provides the path of least impedance for the return current to flow back to the source and establish the reference potential for the voltage—hence its name.
If you do not pair them this way, you cannot expect to contain the fields, and will likely face EMI problems.
The picture here shows some common mistakes I often see when choosing the stackup.
I hope this helps.
Dario
