Re: gEDA-user: Eliminate separate Vcc planes?

[Gabriel Paubert <paubert@xxxxxxx>]

On Mon, Oct 19, 2009 at 10:07:00AM -0500, John Griessen wrote:
> Andy Fierman wrote:
> > So your consultant thinks it's a bad idea to have a Vcc plane because
> > it takes up space 
> .
> .
> .
> 
> > Hopefully you can gently persuade your boss that this is not quite
> > what the very expensive consultant meant to say.
> 
> So, are there no conditions where leaving out a VCC plane makes sense?
> He might not have meant to compare to 3GHz motherboards.
> 
> If he meant to deal with RF transceivers as special case zones,
> and the rest of the circuits operate below some clock speed like 600MHz,
> I can imagine a stack up like:
> 
> for a four layer board...
> 
> signal  + VCC
> =============
> GND1
> =============
> signal2
> =============
> GND2
> =============
> signal3  + VCC2
> 

Congratulations, you've fitted 3 signal planes and 2 ground planes
on a 4 layer board!

I must admit that making an additional plane come out of nowhere
would sometimes simplify my boards...



> 
> or for a six layer board
> 
> signal1
> =============
> signal2
> =============
> GND1
> =============
> signal3
> =============
> GND2
> =============
> signal4
> =============
> signal5

Again, 5 signal planes plus 2 ground planes out of 6.

Lack of caffeine?

> Now if we could just specify blind vias easily with pcb...

Holy grail. But first thing (even for 3 D viewing) would
be to be able to specify a Z coordinate for each layer, layers
with the same Z corrdinate being merged.

	Gabriel


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