Proper way to route an isolated ground polygon

I plan for my USBC connector (flag 90 degree style) to have it’s shield GND run from the shield to the mounting hole and over down into my chassis. I don’t want anything else on GND net, layer 4, to run to this mounting hole. What is the correct way to get the blue polygons I have drawn to actually be properly connected with thermal relief to the USB mounting holes (pins marked 25 GND) while still routing them over to the GND mounting hole on the right? I have spent too much time on this already and am getting frustrated with my lack of understanding how to create keepout perimeters on this polygon but still leave it connected to GND.

I suppose I could put SHLD on another net but then I would get conflicts when the mounting hole ties to my L2/L3 GND pours.

You should not call it GND at all, but some (any) other name. Maybe call it “Shield” or “Earth”.

Then use a “Mountinghole with pad” in your schematic and connect it to the correct pin for the outside of the USB connector. In this way it becomes a separate net, and you can just draw tracks, or create a simple zone around it.

I understand that you want poligon to be solid connected to hole and by thermal relief to USB and it is the problem you ask.
I think you have two choices:

  • you can define zone connection style as solid and modify connection style of USB socket to be thermal relief, or
  • you can define zone connection style as thermal relief and modify your hole connection style.

The problem I also face is that I have an L4 ground pour over the whole board. When I define a zone around the USB socket, the L4 zone and the USBC zone short together. I want to have an “island” of GND running from USBC to mounting hole.

So just for clarity: I understand you want a small zone, which is connected only to the mounting hole and to the housing of the USB connector?

If you create a separate net for it as I suggested in my previous post, and create a zone for it, then you can set the Zone Priority Level to a higher value as from the other zones. Then KiCad draws this zone first, and other zones are drawn around it while respecting the normal clearance rules.

I run into problems because I’m not sure how to tell it that the mounting hole is the same net as the shield. Making a separate net means I get drc errors and I’m not sure kicad will let me. Unfortunately I’m away from my PC now but maybe I will try this and see if I can get it to let me short SHLD to GND without problem.

Just like any normal net:
Have both represented in the schematic, and draw a wire between them.

Why would that result in:

I feel some kind of misunderstanding, but I fail to grasp what it is exactly.
Have you worked before with zones and different priority levels?
Do you know how they work?

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