I understand that the return current will use the closest plane to the signal trace. So could you give me answers on these 2 specific conditions.
1)When we have lets say 4 layers where layer 1 2 3 are signal layers and continuous ground plane is at 4th layer. For all 3 layers' signals the return current path will be on 4th plane right since there is no other plane.
2) Now for second case, the 4 layer stack up is signal ground-plane signal signal. Assume that layer 3 have signal traces but i also poured copper for some vcc rails on some areas of layer 3 (not completely). Then if i draw a signal trace in 4th layer, will the return current be on ground plane at layer 2 or the partial copper pour on layer 3 for trace passing under partial copper pour and trace not passing under partial copper pour.
I hope i am clear.