Re: gEDA-user: next PCB release - 1.99za vs 4.0

[Andrew Poelstra <asp11@xxxxxx>]

On Sun, Sep 12, 2010 at 03:40:24PM -0400, DJ Delorie wrote:
> 
> > > With flex cable, "top" and "bottom" aren't limited to one layer each.
> > 
> > Aren't they?
> 
> No.  Different areas of the cable may have extra layers or pcbs
> attached, changing the number of layers in that area.  So one drawing
> layer might be "top" on the left side of the cable, but "inner" on the
> right side.
>

Should we support this? What problems will we encounter if we allow
layers to have arbitrary geometries?

It looks to me that our "top/inner/bottom" distinctions will then only
appear (a) in footprint mode and (b) when importing footprints. In all
other cases, we simply have a layer stack.
 
> > What use case is there for layers that map to multiple physical layers?
> 
> Single solder mask for both sides.  Keep-outs.  copper heatsinks.
> stripline.
>

All of these make sense for individual components, not for entire layers.
 
> > > Why one?  Why not save it?  We already save rats to file.  What about
> > > layers that don't correspond to a physical layer?
> > > 
> > 
> > Why have a different number than one? I could not think of a good reason
> > for this.
> 
> autorouter might use it to store information.  DRC might.  I don't
> know what future uses, it just seems that "one" is a special case.
> Why not just have a "save me" flag, and let each layer decide if it
> needs to be saved or not?
> 
> Paste buffers (cut-n-paste, not solder paste) might need multiple
> temporary layers.
>

What are we talking about? I meant one layer-stack per board. Adding multiple
virtual layers for whatever you can think of, is fine.
 
> > > keepouts are just another layer.  Let DRC worry about what to do with
> > > it.
> > 
> > Ah, but what happens when you want a keepout on all layers? On one layer?
> > For only HV lines? For footprints but not traces? All these have been
> > mentioned on the list, and don't work well with "keepouts are just another
> > layer".
> 
> I meant, if you have a keepout layer, it's just another layer.  I
> didn't mean to imply that there weren't other ways to specify
> keepouts.
>

Fair enough.


Andrew
 


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