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I have a PCB design that requires two ground pours on the bottom layer, one is AGND and the other is DGND. Most of the board is AGND ('L' shape) and the remaining should be DGND.

I have tried to pour polygon with AGND over the entire board, draw another polygon for cutting a square out of the AGND pour and tried drawing yet another polygon for DGND. I think this is a naive approach and it did not work.

If anyone can enlighten me it would be super!

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  • \$\begingroup\$ Cutouts cannot be ordered and cut through all polygons. Suggest unit128_t's method. \$\endgroup\$ – Spehro Pefhany May 22 '16 at 0:28
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Option 1: Just bite the bullet and make the AGND pour in an L shape.

Option 2: In the polygon manager, adjust the pour order so the DGND pour happens before the AGND pour.

I'm not clear what you mean about "draw another polygon for cutting a square out of the AGND". If DGND is poured first, and your design rules are set correctly, Altium will respect the different nets clearance rule and produce a clearance between the DGND polygon and the AGND being poured around it.

However I actually prefer the first option because it is less likely to cause trouble if you edit the design later, shelve some of the pours, need to add a new polygon that overlaps the first two, etc.

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  • Draw the AGND polygon pour over the entire board.
  • Draw the DGND polygon pour where you want it.
  • Set the DGND pour priority to something higher than the AGND pour (this is somewhere in the pour settings IIRC *see below).
  • Altium should repour the AGND pour.

If something's not right, check your clearance settings. Basically, a poly pour with a lower priority should "wrap" around a higher priority pour with clearance set by DRC settings.

*edit: rats, I think I'm misremembering Altium with Kicad. In Kicad, you can easily set pour priority, but it's not so easy in Altium. However, you should be able to edit pour order in the Polygon Manager, which has a list of polygons and lets you adjust the order.

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You can also create the shape in a CAD program, which is a lot more flexible than trying to use Altium's primitive drawing tools, and then export the shape in DXF and then import it onto a mechanical layer and use "convert selected to polygon fill" to create an arbitrary polygon.

Unfortunately it cannot properly handle shapes with internal cutouts.

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