Signals and plane on the same layer
Hi, I’m working on a PCB layout, which is only about the second board I’ve ever designed. I’d appreciate some help with a few basic things. I’ll split my questions into separate posts.
This board has two layers:
-
The top layer is used for signals and power planes.
-
The bottom layer (shown in the images) is intended to be a ground
plane.
I’ve tried to minimize the number of traces on the ground layer, but in some cases, routing constraints leave no choice.
My question is:
When placing traces on this ground plane, is it better to:
- Keep them as tightly packed as possible, grouping them into a concentrated "island" within the ground pour (Image 1)?
- Space them out slightly, allowing the ground pour to flow between them, thereby increasing the overall ground area surrounding the traces (Image 2)?
Additionally, a large power polygon runs above these signals on the top layer, meaning the traces are effectively crossing underneath it.
Maybe these images don't demonstrate the issue very well, but I’d love to hear your insights on the best approach anyway.
1 answer
My answer from another place: -
It's best to use a 4 layer board looking at the tracks you have on your ground-plane side.
But, if you are really insistent on using only two layers (why?) then do whatever you can to minimize the track lengths on the ground side. I would say from experience in answering this type of question on this site that you have almost certainly (a probability thing) not minimized the track lengths on the ground side so, please do so.
Work on the top layer tracks and do what you can. If necessary go from top to bottom then back to top then, back to bottom and then back to top to keep the ground-plane as uncluttered as possible.
If you are going to group tracks, keep the group small and leave a good amount of ground plane between adjacent track-groups.
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