From: Luis Moreira <luis.moreira1575@googlemail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Sun, 13 Sep 2020 05:31:08 -0700
Subject: Re: [EE] Four Layer Routing Strategy
Thread-Topic: [EE] Four Layer Routing Strategy
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Hi All,
I've been doing a bit of PCB layout lately, I'm actually doing a 500KHZ
bandwidth analogue optical link at the moment. Obviously noise issues are
very high on my list of issues to avoid.
The layout strategy you are describing seems very good, but I gave a few
questions:

- What do you do with through hole components?

- how do you deal with a surface mode power supply for the circuit board?
You will have to place it on the top routing layer  but do you immediately
get vias to the power layers?

- The vias crossing from the routing layers through the power layers, will
this  not create other issues?

On a sightly different subject, on a two layer board I tend to run power
and routing on the top layer and ground layer mostly as a copper poor on
the bottom layer, is this best practice?

Thank you.
Best Regards
               Luis

On Sun, 13 Sep 2020, 12:57 Alan Pearce, <kiwiantipodean@googlemail.com>
wrote:

> > Ok, sounds like keeping the inner layers as ground and 3.3V separately
> > will be the best. No problems there.
>
> That is the 'normal' way to do it. And using manhattan routing gives
> you a good starting point. Once you have the board routed you can look
> to see where the routing can be tweaked to minimise vias.
>
> > One thing about planes though, I once read an article about being
> > careful using planes, that essentially small ground loops could form
> > in them.
>
> Opinion on this has gone back and forth like a leaf in the wind, but
> one of the most authoritative texts I have seen was an appnote or
> article from ADI which advocated having one complete ground plane with
> minimal distinction between digital and analogue ground. It doesn't
> mean you could mix the digital and analogue parts willy nilly, some
> care is still needed with relative parts placement.
>
> On Sun, 13 Sep 2020 at 02:57, Josh Koffman <joshybear@gmail.com> wrote:
> >
> > Thank you all for the advice!
> >
> > Ok, sounds like keeping the inner layers as ground and 3.3V separately
> > will be the best. No problems there.
> >
> > One thing about planes though, I once read an article about being
> > careful using planes, that essentially small ground loops could form
> > in them. Since then I've always had my planes as a separate net (ie
> > not ground), and I connected them to the ground traces strategically.
> > Each area of pour had only one connection to ground.
> >
> > Should I be using the pours a bit more liberally and letting them join
> > all the pins on that actual net? That's easily done (actually easier
> > than the way I have been doing it). I'd add thermals in to try to help
> > make it easier to solder.
> >
> > The board service I've been using lately doesn't allow for
> > blind/buried vias without a hefty upcharge. I am definitely not at
> > that level, that's for sure!
> >
> > Thank you!
> >
> > Josh
> > --
> > A common mistake that people make when trying to design something
> > completely foolproof is to underestimate the ingenuity of complete
> > fools.
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