Re: gEDA-user: PCB suggestion

[sdb@xxxxxxxxxx (Stuart Brorson)]

> > > > How is this done in Orcad? In Eagle? In other tools? 
> > > 
> > > Since it's an internals problem, and not a user interface problem, we
> > > have no way of knowing.
> > 
> > In PCB you cannot draw a rectangle of missing soldermask.
> > 
> > Cna you in Orcad? Or in Eagle?
> 
> Oops, sorry, I misunderstood the question.  I don't know.

Usually you can draw on any layer you want.  Most tools have a
separate soldermask layer (as well as a solderpaste layer), and you
can draw on it to your heart's content.    

Indeed, you can usually define layers as either "positive" or
"negative".  If you draw a rectangle on a positive layer, then you get
a rectangle of whatever that layer is -- metal, silkscreen, mask,
whatever.  If you draw a rectangle on a negative layer, then you
remove a rectangular area of the material from which that layer is
made.  Mask layers are usually negative layers, IIRC.  (Somebody can
correct me on this since I am not a layout designer.)

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.  A difficulty will be in tying
which silk & mask belong to which metal layer (top or bottom).
Perhaps the config would be:

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

In this case, the program knows to draw voids in the mask_top and
paste_top when you draw metal on metal_top, for example.  Otherwise,
it gets too confusing.

I think that DJ knows this; in any event it is a major change from
what we do now, and represents a lot of development work.  If DJ or
somebody else takes this task up, then we all owe them a great big
"thank you"!

If you want to puruse this further, try downloading one of viewer
programs which are freely available from the big EDA players and look
at their default layer setups.

Stuart