On Mon, Sep 8, 2014 at 11:10 PM, peter green <plugwash@p10link.net> wrote:

> V S wrote:
> > However, with respect I want to remember you all, that a good PCB
> engineer
> > will probably never use 20 layers for the most complex design ever
> made...
> >
> > Keeping thing simple is the key for everything.
> >
> Something to remember is that 20 layers doesn't mean 20 signal layers,
> as the speed goes up the proportion of the layers that can safely be
> used for signal routing goes down.
>
> Combine high speeds with a need for heavy double-sided population
> (rather than just a few caps on the back) due to space constraints and I
> could easilly see a 20 layer requirement becoming legitimate.
>
>
   Of course 20 layers does not mean 20 signal layers. Ground layers can be
used with success for clocks, differential  signals as well analog signals.
There isn't any BGA package yet from which you can't escape in max 10
layers. The smallest pitch the biggest headache.   20 layers is legitimate
for NASA or for other people which don't want to get headaches during a
project design...
--=20
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