kicad-developers team mailing list archive

["Brian F. G. Bidulock" <bidulock@xxxxxxxxxxx>]

Alex,

On Mon, 11 Oct 2010, Alex G wrote:
> 
> Please guys, stop arguing. I agree with changing the base unit system to
> metric, and I have already voiced that opinion. No one tried to chop my
> throat. If it makes sense to switch to metric why not do it?
> 
> The real question is wether it makes sense.

I have several 1000-ball BGAs on a metric pitch.  Every other ball is off
its position by part of 1/10000th of an inch.  No problem?  Well when
pulling dogbones for BGA breakout, I wind up with about 1000 0.1mil segments
connecting the imperial gridded vias to the imperial gridded balls.  So
I tried unlocking the 45-degree tracks pulling slightly off 45-degrees so
that there were no 0.1mil segments.  Instead I got 1000 DRC errors (yeah,
its tight in there), and a thousand 0.0mil segments.  Then there is the
performance problems associated with drawing thousands of 0.1mil or 0.0mil
traces.  Hard locking to a 10 nanometer minimum grid would remove all these
problems.  Any time pads, pins or lands are on a metric pitch, the same
problems arise.

The maximum precision allowed by RS-274X is 6.6 for metric, so it makes
sense to use 1 nanometer as the internal unit.

--brian