Copper fills


I got my first self designed PCB back from manufacturer today. Proud moment. There is an error in it. Why do we only notice error once they have been printed? Anyway, its easily repaired with a jumper wire.

I noticed a difference between my design and the professional PCBs that I have, designed by others and that is copper fill. Professional PCBs have island areas of copper and I understand that copper fill would be good for stopping EMI.

I wonder if it is possible to do a Boolean operation on existing tracks on front or back copper, or both, so that the " island" areas are still filled with copper and the tracks are simply isolated from that. I tried to read a few posts and look for some YouTube tutorials but came up empty handed. I can’t find anything in the PCB editor.

Thanks for your help.

Sounds like you just didn’t untick the “remove islands” option in the plane pour?
In general it is rather contraproductive to have isolated islands, since they are stray capacities.

Areas of copper are called “Zones” in KiCad. You can create them with: PCB Editor / Place / Add Filled Zone.

Yes, this is normal behavior in KiCad. Each of the zone is part of a net and connects only to that net. It (semi) automatically keeps an (adjustable by you) clearance from all other nets. These copper zones are not “random”. In general, it’s good to start with only connecting the GND net to a zone, make that zone as big as possible and keep any other nets away from that zone (Put them on the other side of the PCB).

Apparently you have not used KiCad much yet. It’s one of the basic concepts in KiCad (and PCB design. How these zones work and affect EMI and signal integrity is a whole study on it’s own. It’s also an important topic that does need some studying, so put some time and effort into that.

As paulvdh says, you need to look at zones.
So, for my PCB’s, I want the gnd-connected zone to fill the gaps over my complete pcb, on BOTH sides, so:

  • On FRONT, add a zone that surrounds your complete PCB… so yes, it will be OUTSIDE of your edge cuts. You make the zone by adding lines, these must come back exactly to the start point to close the zone. Make sure this zone is set to connect it to the ‘gnd’ net.
  • repeat this on the BACK
  • get Kicad to actually fill in the PCB: I usually just run the DRC checker (which does a “refill all zones” as its first step), but you can also just do a “Edit / Fill all zones”.
  • if you have any areas that Kicad can’t fill (ie an isolated island), then drop a (gnd) via to the other side where there is already gnd (probably a gnd zone created above!). Repeat the ‘fill’ step. Repeat this step as needed to fill other bare areas.

My pcb’s are small audio boards, some have a bit of digital control: any high-frequency areas are very small (eg the crystal), so having a complete ground plane / multilayer pcb would be overkill. So, I just do as above, and fill the large open areas with ground fill. One side has mainly vertical tracks, the other mainly horizontal tracks.

Something you may want to think about is whether any mounting holes should be isolated (that’s what I do) or connected to gnd (probably best not to do unless you are 100% sure of the implications of doing this!)

Thanks again for these excellent tips and for sharing your knowledge. I appreciate it.

Thanks so much. Lots of good things happening now.
How many vias linking top and bottom fill zones are required?

yes this is very true but isn’t it so much fun.

I guess a lot is going to depend on what the board is used for. If you have “isolated islands” of copper, then the fact that they are isolated means that there’s actually no active current going through them… like me, you will be using them to (a) balance the amount of copper on each side of the PCB; (b) act as a sort of “screen” for other signals.

So I guess you don’t need to go mad: I just looked at one of my audio boards, and where there’s larger copper fills, I have vias about every 5mm. Think like you’re gluing paper to card: a load of blobs around the edges, then a nice grid of them in the middle!

If, however, you are talking about a high-speed / high-frequency circuit, then the rules will be a bit different, I’ll just light the blue touch paper and walk away, leaving others to comment!