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I read in some places that having a solid ground plane is needed . Does not via stithing causing the solid ground plane to become broken? Is this okay?
Also when everyone talks about return current, are they talking about the current flowing underneath the trace itself or the plane beneath the trace?(because skin effect makes a trace a 3d structure, can return current flow below on the same trace?)
Stitching vias are typically used to connect multiple ground planes on different layers together. Since they are connected to ground there is no break in the plane other than the drill hole which is negligible. Return current flows on the plane directly under the trace but spreads out some distance from trace with the strength of the field dropping off further away from the trace. Typically a distance of 3 to 5 times the width of the trace or dielectric height is used to determine spacing to an adjacent trace that will not result in significant cross talk. Although current flow is on the surface of the trace and ground plane (due to skin effect) the field is actually in the space between the two conductors.
Also when everyone talks about return current, are they talking about the current flowing underneath the trace itself or the plane beneath the trace?(because skin effect makes a trace a 3d structure, can return current flow below on the same trace?)
I assume you're talking about microstrip line, so there is only one ground plane, "below" the trace. (Not stripline where there will be ground planes both above and below the trace)
The signal current flows in the trace and the return current flows in the ground plane.
To the extent that skin effect plays a role, most of the signal current flows on the surface of the trace closest to the ground plane. And the return current flows on the upper surface of the ground plane near-ish to the trace.
Does not via stitching causing the solid ground plane to become broken? Is this okay?
Stitching mostly makes sure that all of your ground planes are at the same potential. It can prevent a semi-isolated region of ground plane from acting as an antenna and producing radiation.
It is a good idea to keep stitching vias at least a few trace widths away from any high speed microstrip traces. Then they will have little effect on the return currents associated with the microstrip.
