kicad-developers team mailing list archive
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Re: Patch to display mm to two dp instead of three
Wed, 22 Jul 2009 07:50:20 -0000
--- In kicad-devel@xxxxxxxxxxxxxxx, Brian Sidebotham
> I remember some musings on the list about increasing the internal
> resolution of KiCAD, but I don't think there has been any discussion
> about that for a while.
I would like to do a reality check about the needed resolution:
- First of all the minimum feature size I've seen supported by board fabs is 4 mil (about 0.1 mm). And with premium tooling (and associated costs)
- Drilling is done with 0.1 mm tip increments (and to go below 0.4 mm you usually have to use laser microvias)
- Pick'n'place/drill positional accuracy is AT BEST +-0.02 mm (with a more popular 0.1 tolerance)
Given this average production limits I'd say that two decimals on mm is enough (and the internal resolution of a decimils would cover a lot of things).
OTOH I've seen brochures for CAM products importing GDS-II streams (the stuff for chip manufacturing IIRC) for doing PCB microfabrication :P
Just for curiosity, what kind of unified grid are you using? The 0.5/0.05 metric one or what? I usually put mechanical features on a 0.5 mm grid and components/tracks on a 20 mil one (falling back to 5 mil for difficult areas). Mind that I'm usually doing work double face on relatively big components (0603 passives and 0.5mm pitch TQFP, usually) and relatively large voltages (almost all my boards have AT LEAST 12V running on them); the need for class III environmental clearance doesn't help too...