for Dc they go wherever they feel like. as frequency goes up they follow the path of the signal above.
Yes, and no.
As I showed, DC (1KHz I used is close enough) does not just go "wherever they feel like" into the dead end voids etc.
Dave.
[/quote]
let me rephrase that.
for low frequencies they will attempt to follow the most direct line between source and destination. they travel in a relatively wide band. of course they won't go in sticking-out-swaths of copper if there is no point in going there.
as frequencies increase they will tend to follow the path of the source signal.
DC
________________________________
| |
( top layer) in ------ |
--------- out
|______________________________|
(plane) GND ------------------------------------------------------------------------------- GNd return
RF
________________________________
| |
( top layer) in ------ |
--------- out
|______________________________|
________________________________
| |
( plane) in ------ |
--------- out
|______________________________|
kind of hard to do in ascii ..
if you have a meander trace over a solid plane : for DC or low frequency the ground return current ( current coming back from the load , through the ground , to the source ) will flow in a straight line. ( top drawing )
for RF : the return current will follow the shape of the meander above the plane. it will not go for the beeline but run exactly in the same shape as the trace above, even if there is a solid plane and no reason to do that.