Re: gEDA-user: PCB suggestion

[sdb@xxxxxxxxxx (Stuart Brorson)]

> 
> > Moving forward, it would be best if PCB didn't hardcode the concept of
> > layer type into specific layers.  Rather, you should just define
> > whether the layer is silk, mask, or metal, and additionally define
> > whether it is positive or negative.
> 
> That is a very BAD idea. PCB is not a drawing tool; it understands things
> like design rules, connectivity etc. It makes no sense to have software to
> trace connectivity on the silk, mask, keepout, etc layers or to not be able
> to understand that metal layer DRCs are different from the silk layer, or to
> deal with elements having various "grouped" metal, mask, and silk features
> if all layers were arbitrary.

Yeah, I agree.  I wasn't focussed on thinking while writing this
particular paragraph.  I *do* think a built-in stack-up like that
which I suggested: 

silk_top (pos)
mask_top (neg)
paste_top (neg)
metal_top (pos or neg)
int2 (pos or neg)
int3 (pos or neg)
etc. . . . 
metal_bot (pos or neg)
paste_bot (neg)
mask_bot (neg)
silk_bot (pos)
Assembly (pos)  (perhaps have top and bottom?)
Board outline  (or just consolidate with Assy layer?)
Drill

makes sense.  Then, the program will know that if I put a pad on teh
top layer, it will put the right metal_top rectangle down, cut the
right void in mask_top & paste_top, and so on.  It will also know that
if I place a via, it should connect to the metal layers where
connectivity is present, void the layers where connectivity is absent,
and not void out the mask, unless the via is a test via.  The prog
would also have the notion of various DRCs built into it.  I agree
that the layers can't be aribtrary, because that would make building
the DRC checking and connectivity & mfg rule awareness difficult.  

OTOH, I don't like the current layer arrangement in PCB, which
provides separate tabs for metal_top and GND_top (i.e. plane), and so
on.  There should be one tab per layer & you should handle plane
vs. routing layer issues using positive and negative layers.

Stuart









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