From: David C Brown <dcb.home@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Sat, 12 Sep 2020 10:37:02 -0700
Subject: Re: [EE] Four Layer Routing Strategy
Thread-Topic: [EE] Four Layer Routing Strategy
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The most complex board I designed just before retiring had 14 layers which
had several power and ground planes (and which worked well at
several hundred meg)
I never mixed ground and power on a single layer though I might have more
than one voltage plane on a layer.

So I would advise you to have a solid 3.3 volt plane on layer 3.  That way
you are running your signals on both outer layers over a plane; you are
reducing the impedance of the 3.3 volt distribution; and you are providing
a useful distributed decoupling capacitor
__________________________________________
David C Brown
43 Bings Road
Whaley Bridge
High Peak                           Phone: 01663 733236
Derbyshire                eMail: dcb.home@gmail.com
SK23 7ND          web: www.bings-knowle.co.uk/dcb
<http://www.jb.man.ac.uk/~dcb>



*Sent from my etch-a-sketch*


On Sat, 12 Sep 2020 at 18:13, Josh Koffman <joshybear@gmail.com> wrote:

> Hi all,
>
> I'm working on my first 4 layer board. I feel a bit like I failed
> cramming it all into two layers, but I recognize that having so many
> vias on every trace would be less than ideal.
>
> I'm using top and bottom for signals, then the inner layers for power.
> The board isn't anything crazy RF, just some regular digital signals.
> There is some digital audio on the board, so there are a few "medium"
> frequency traces.
>
> I plan on using the top inner layer for ground. I'll do it like I
> normally do, which is to route the ground traces manually, then do a
> pour that connects to the ground trace in one place.
>
> On the bottom inner layer I'm going to route my 3.3V traces. There
> will be a lot of free space on that layer.
>
> So the question is, what should I do with the free space on the 3.3V
> layer? I could do either a 3.3V pour or another ground pour. I lean
> towards another ground pour but I don't want to inadvertently create a
> weird capacitor.
>
> Any suggestions? Since this is my first time I'd like to not have to
> re-make the board because of this particular error!
>
> Thank you!
>
> Josh
> --
> A common mistake that people make when trying to design something
> completely foolproof is to underestimate the ingenuity of complete
> fools.
>         -Douglas Adams
> --
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