Author Topic: Kicad - local net clearance, or better way to do transmission line?  (Read 4367 times)

0 Members and 1 Guest are viewing this topic.

Offline c4757p

  • Super Contributor
  • ***
  • Posts: 7805
  • Country: us
  • adieu
Simple question that may or may not have a simple answer:

I'm trying to do a 120 ohm PCB transmission line in KiCad. (Specifics: grounded coplanar waveguide, 0.2094mm trace, 0.6mm to surrounding ground plane, 1.6mm FR4) I've done this by defining a net class with the trace width and spacing. The problem is that after the termination at the end, it needs to go into a pin on a SOT-23-5, which doesn't have enough space to the next pin. I can change the clearance for that pad, but it of course doesn't change the clearance of the trace itself, which DRC will still not allow to come near the neighboring pads.

Is there some hidden way that I'm not aware of to locally switch net classes? (I doubt it - KiCad is sorely lacking in "professional" features like that....) Or, is there a better way to do this? Obviously, short of just setting the clearances to zero and drawing the zone manually to the right spacing...
No longer active here - try the IRC channel if you just can't be without me :)
 

Offline andy1

  • Contributor
  • Posts: 25
  • Country: fi
Re: Kicad - local net clearance, or better way to do transmission line?
« Reply #1 on: September 10, 2013, 07:48:49 am »
Not entirely sure if this if what you want but one way to do this would be to have the trace width at the spesified 0.2094mm but don't set the clearance to the high value of 0.6mm, keep it at 8-10 mils or some other suitable value for routing.
Then change the copper zone clearance to the required 0.6mm, you can also do multiple zones if you want the copper closer to some other parts. I agree that it is kind of roundabout way to do this but I guess doable.
 

Offline c4757p

  • Super Contributor
  • ***
  • Posts: 7805
  • Country: us
  • adieu
Re: Kicad - local net clearance, or better way to do transmission line?
« Reply #2 on: September 10, 2013, 08:43:05 am »
That's pretty much what I ended up doing.

God, I love KiCad, but whoever wrote the zone tool code needs to be flogged.
No longer active here - try the IRC channel if you just can't be without me :)
 

Offline johansen

  • Frequent Contributor
  • **
  • Posts: 730
Re: Kicad - local net clearance, or better way to do transmission line?
« Reply #3 on: September 10, 2013, 02:17:02 pm »
the only problem with multiple zones is kicad has issues with zones inside zones on the same net.

i've tried to do a donut type zone few weeks back, I managed to do a 2-D mobius strip type zone that got almost what i needed, then put a trace across the X shaped section that didn't have any copper fill.

I'm running the daily testing build, and for about a year i never ran into any serious bugs that weren't fixed within a week, but Adam Wolf dropped support for ubuntu 10.04, so its not been updated since march 2013. i haven't noticed any bugs in the version i have, but they have probably added a lot of stuff since then
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf