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My first 4 layer PCB
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Spark-Doctor:
Hi all

I am laying out my DC Load project and it has become apparent that it will be a lot easier if i go to a 4 layer board.

The board is 235x170mm. I don't need it this big but is was always going to be bigger than 100x100 and the board flipper did not penalise me for jumping to this size and i have designed it to fit the bottom of the case i am putting it in.

After a lot of research, i propose my layer stack as,


* Arduino Nano and control circuits
* Ground
* Load
* Other power Circuits
Questions

1) I have several negative voltage rails, which layer should they go on?
2) On the "load" layer, is it better to just flood the entire layer even though i don't need that much area or can i split it in 2 and with an
    appropriate gap, have 2 different voltage planes on the same layer?
3) I have a mixture of SMD and through hole so rater than lots of via's, i was going to flood the top layer with a ground as well. Good or Bad?

This will probably be the first of many questions :-DD

Thanks in advance

Ian
 
DaJMasta:
I wouldn't put load traces on the inside.  Typical stackup is signal, ground, power, signal as a general guideline, but typically inner copper layers are thinner (half ounce, usually), and since they're on the interior, any heating takes much longer to dissipate, so it's not ideal for high current stuff.  If you run a primary power rail on the interior, have a ground that is essentially uninterrupted, then maybe keep analog on one and digital on the other, you should be able to do most of what you're looking for.  If you need multiple rails, you can divide up the power plane (or route traces to specific places), but it may be simpler and better for the stability of that rail to just use a wide trace on the top or the bottom if those other rails are only going to a couple places.


By the size of the board, you probably don't have so many traces that you'll have to sacrifice much in terms of organization to get everything routed (maybe a double sided with a few jumper links would even do the job), so I'd make an effort to leave the power and ground planes uninterrupted (and single rail on the power plane), and then if it seems like the routing is nasty somehow, consider breaking the power plane for other rails then.
jbb:
I totally recommend using a whole layer for a big group plane, and trying hard not to cut it up.  The second inner layer should probably be power distribution.

I recommend keeping your inner layers as simple as possible, because they’re nearly impossible to wire mod.

I usually pour ground over all layers and stitch them together with vias (maybe 15mm spacing? Or 5mm if you’re sticking BT / WiFi on it).
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