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

[Andrew Poelstra <asp11@xxxxxx>]

On Tue, Sep 14, 2010 at 10:34:23PM -0500, John Griessen wrote:
> On 09/13/2010 05:07 PM, John Doty wrote:
> >
> >On Sep 13, 2010, at 2:27 PM, DJ Delorie wrote:
>  So let me rephrase: Why have seven geometric holes,
> >>one for each layer, when we can have one geometric hole applied to the whole composite?
> <snip>
> >My notion is that you need a general mechanism to align objects between layers.
> <snip>
>  Having such a mechanism, you should then use it universally. If
> >you bypass general general mechanisms for special cases, you risk creating a mess
> where general automation procedures fail in
> >those special cases.
> 
> John D has something here -- suppose we start using pcb to model the physical in
> a way that is used to analyze layer stack up alignment of weirdly processed layers?
> For instance layers that get folded and stretch some, and so need alignment checking?
> 
> Perhaps holes get made in one stroke still, but the via pads need a tolerance to be able
> to hit them close enough to their centers with the drill.   Perhaps holes don't even all
> get made in one stroke!  I heard about microvias being made with UV lasers that would be on just a few layers.
> Also there is  a max feasible aspect ratio to a via hole width vs. its depth to drill with carbide bits.
> Some board makers said they handle this by drilling in from both sides.  Take it a little further
> and you make two composites separately drilled, then bond together....
> 
> Sure, all of this is far out, but still worth planning for.
>

I -think- that all these cases are accounted for with:

  1. DJ's composite idea
  2. Distinct canvas/layer structure with tagging
  3. Custom vias

At the very least, we're on the right track.

For custom vias, we will probably want to allow drills in footprints.


Andrew



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