Clearance of copper pours

Layout
1

Hey all,

I’m new to coplanar waveguide pcb layouts, and to do this I am using KiCad. I want to make this RF circuit to have 5 mil clearance around all the traces, and I’m laying down fresh (no netlist pulled in from a schematic). Whenever I try to fill a copper zone surrounding a trace, I never get a spacing (clearance) between the copper plane and the trace. Instead it looks like the copper plane is engulfing the trace. Any advice? I am trying to use a .005" clearance

Thanks for your time!

2

Try this:

  1. Double-click your copper zone. Copper Zone Properties dialog should appear.
  2. Type 0.005 into the Clearance field.
  3. Click the OK button.
  4. Re-run the DRC tool.

Hopefully, you’ll see the traces separated from the plane by 5 mils.

3

Hey devbisme,

Looks like that worked! But it’s only letting me get down to 10mil of clearance…I need 5 mil. Is this a result of the DRC settings? I’ll poke around …

4

This could be because of your minimum clearances set in the Design Rules dialog (“Design Rules -> Design Rules” menu on my version). The default is 0.01, you should try changing that to 0.005. Also note that you should ensure that your board house can handle that, otherwise, you might not get the desired results on your PCB (for instance, the rules at OSHpark are 0.006/0.006)

You will need to play around with the settings, but you may also need to change the Global rules so it accepts any changes to the default rules. Alternately, you can add a Net Class that has special rules (but would still require a change to the global rules).

5

Hey guys,

Chris I think you hit the nail on the head. I changed the defaults around, made the tracks fill in solid (so I could measure the distances correctly), and set the desired values in the copper pour property fields. Got it to work! :slight_smile: such is life as a n00b…

6

and good call on the fab house tolerances - I did find a fab house capable of 5mil trace/spacing, called SpeedyPCB

7

I’m the farthest thing from an RF expert available, but also make sure you get the stackup you need from SpeedyPCB and that they can do what you want. I do know that some people report getting good quality boards for RF from OSHpark.

8

Actually that was the other company I was looking at! I’ll just go with whoever is cheaper haha