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Date: Wed, 23 Sep 2015 12:06:41 +0200
From: "Gabriel Paubert (paubert AT iram DOT es) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
To: "Nicklas Karlsson (nicklas DOT karlsson17 AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
Subject: Re: [geda-user] Apollon the technical thread
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On Wed, Sep 23, 2015 at 11:14:50AM +0200, Nicklas Karlsson (nicklas DOT karlsson17 AT gmail DOT com) [via geda-user AT delorie DOT com] wrote:
> > > For what do we use copper fonts? I used the words "layer 0", "layer 1" 
> > > ... only to indicate correct orientation for the fab house.
> > 
> > I use copper text as poor man's silk when hand-prototyping.  Also, you may 
> > want to be able to identify a layout even when the silk is missing.
> 
> I think only difference between copper font and silkscreen font is the layer, they both en up in gerber. Or I am wrong?

Design rules: for example my PCB manufacturer wants minimal silk screen
of 0.15mm, but for the copper I have choice of 0.15, 0.125, 0.1mm
(actually same cost for 6 layer boards as long as I don't want 
especially thick copper), or even thinner at extra cost.
Inner and outer copper layers may even have different design rules,
although right now the only text I have ever put on inner layers have
been layer markers.

Transforming a random character into a set of Gerber commands that will:
a) respect the design rules (make them thicker if too thin? Trivial for
   strokes, much less for filled polygons)
b) keeps them readable
c) is reproducible over time (version changes) and file transfers between systems
d) respects another design rule PCB right now has no provision for:
   the silkscreen should be on the soldermask, and even the soldermask
   should extend past the silkscreen for at least some minimal distance
   (75µm for my PCB house, they remove non-conforming silkcreen during
   fabrication).

Satisfying all these conditions is a hard problem. 

> 
> > > But even fixed gerber fonts can be stored outside of the PCB file.
> > > Store only version number of fixed font inside of PCB file?
> > 
> > Rule of thumb, if something can go wrong, it will sooner or later go 
> > wrong.  If you want to make sure the letters *never* accidentally change, 
> > even not if someone in the distribution wants to be clever and "fixes" 
> > something in the font without adjusting the version number, then include 
> > the font in the layout file.  There's no easy way around that.
> 
> For gerber files I would say fonts should be stored inside each file.

Fonts do not scale linearly, so would you keep all sizes you use in a
given PCB file? And even keep the characters modified to satisfy a) and
b) above, with a) being layer dependent?

    Gabriel