Is is possible to join the ends of a concave filled copper pour polygon to create a ‘ring’ of poured copper?
Here’s an example: Imagine a 5cm x 5cm square, with a poured copper fill 1cm wide covering three of the four sides of the square. Is there any way to edit the poured area to join the two ends to form a poured copper layer that still has an unfilled square in the center of it?
When I try to do this in KiCAD Pcbnew (version 5.1.7) I get a warning about “Self-intersecting polygons are not allowed.” Any workaround for this?
This is a real problem for me, and not just a hypothetical mental challenge. In my design, I have +12v distributed to the center components on the board, and GND in a ring around the outside.
No. This is not possible in KiCad.
A copper zone is a single polygon with no overlapping of self intersecting allowed.
But there is another method that gets you the same result.
Draw the zone itself as a completely filled area.
Draw a “Keepout Area” inside the zone.
The “Keepout Area” is one icon lower then the zone. It can act on multiple copper layers at once and you have toggle settings to keep out any combination of tracks, via’s or the copper pours of zones.
Duh, silly me.
Indeed, just draw several zones inside each other, As radix suggested. The zone with the highest priority is poured first, then a zone with lower priority keeps it’s clearance from that zone while being poured, etc.
And if you really want to get complicated:
It is possible to create two zones and connect them to the same net. These will have no clearance for overlapping sections and will act as a single zone for all practical purposes. Beware: I wrote it’s possible. I do not think it is a good idea to do so.
This sounds solvable by increasing the priority to the +12 V zone. Using that you don’t need to draw a complicated GND zone, as it will be automatically filled around the +12 V zone.
Unfortunately concave polygons are simply not supported (I guess a Gerber stipulation) so you have to synthesise the effect additively or subtractively as shown in the previous replies.
Thank you so much for the explanations, and all the suggested solutions. I’ll try to implement one in my design, but I learned a lot from understanding them.
So I looked up what a “concave polygon” actually is:
And concave polygons are fully supported by KiCad. It’s such a simple concept that it is not even a question.
Self intersecting polygons are however not supported.
and I’m quite happy with that. Self intersecting polygons for Zones create confusion and ambiguity. It is just a bad idea to try to use this in the context of Zones in KiCad.
I vaguely recall some forum post about self-intersecting-polygons for graphics on this forum, with pictures from .svg files in Inkscape and that’s another subject. I’ll leave that out of the discussion of copper Zones.