Mail Archives: geda-user/2014/06/26/12:19:35
On Sat, 2014-06-21 at 12:27 -0400, DJ Delorie wrote:
> > I "think" if gerber supports them, then getting arbitrary axis
> > directions will still be awkward / impossible without approximation.
>
> Gerber doesn't support them. At least, not reliably across fabs. We
> approximate them with line segments.
Speaking of Gerber - at some point, we should re-validate our output
choices against current UCAMCO recommended practice.
I would suggest that we re-enable arc features in gerbers at some point,
and see if we identify any fabs which still have issues. (They ought to
fix their end, not be a reason to reduce the fidelity of our output).
I know we do polygons "wrong", with stitching of pieces without holes. I
vaguely recall that we used to do it the "right" way, but changed for
sake of compatibility with bad fabs.
UCAMCO have recently issued a white-paper stipulating the "proper" way
is to alternate positive and negative layers, I can see how this would
help CAM software to process things nicely, and as a benefit - it would
speed our output quite a bit for complex boards.
Similarly - do we stick to their recommended best practices of ONLY
creating pads using a single flash of a single aperture? The white-paper
citing this recommendation explains that this structure is used to allow
the CAM tool to extract pad locations more reliably, and that ATE flying
probe testers will use this extracted data to identify probe points.
Perhaps unfortunately, most PCB vendors I've encountered won't complain,
or highlight any deficiencies in our gerber files when compared to other
packages. They just "make do", and won't admit you are costing yourself
extra time and money because some part of the process isn't going 100%
smoothly, or that they are hand fixing up the data.
Peter
--
Peter Clifton <peter DOT clifton AT clifton-electronics DOT co DOT uk>
Clifton Electronics
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