Electronics > Beginners
4-layer stackup options
jrs45:
I've been reading about PCB stackups, and for four layer boards, there are usually two popular options (bottom to top):
Signal - power - GND - signal
GND - signal/power - signal/power - GND
I've typically used the first one, it seems to be the most popular (and having access to traces is handy for bodging).
The second one, with GND planes shielding the signals makes a lot of sense, since when peppering it with grounded vias you can make a pretty good faraday cage around the inner signal/power layers.
But doesn't the large number of non-GND vias break up these ground planes significantly? You'd need one for just about every pin connection, so it seems that a large amount of the ground plane(s) will be broken up like crazy, at least when you have a dense board (as many do). And these vias travel through all layers, interfering with optimal routing.
Just wondering what people thought of this.
thinkfat:
I thought the most popular stack up was signal gnd power/signal signal. To be able to route controlled impedance traces on the top layer.
jrs45:
--- Quote from: thinkfat on February 20, 2020, 03:39:06 pm ---I thought the most popular stack up was signal gnd power/signal signal. To be able to route controlled impedance traces on the top layer.
--- End quote ---
That's what I wrote, I just wrote from bottom to top.
Neilm:
I would not put a plane on the outer layers - it would make routing the board hell. The ICs and components will make a mess of the plane. If you have any high frequency they will become very small slot antenne.
Also, the two planes close together will act like a capacitor giving you some high frequency decoupling.
jrs45:
--- Quote from: Neilm on February 21, 2020, 05:02:26 pm ---I would not put a plane on the outer layers - it would make routing the board hell. The ICs and components will make a mess of the plane. If you have any high frequency they will become very small slot antenne.
Also, the two planes close together will act like a capacitor giving you some high frequency decoupling.
--- End quote ---
That's what I was thinking, but it was surprising to see it so widely advocated I figured I was missing something. Having the outer layers as shields does make sense, until you realize how much these are broken up by components and vias that will be basically everywhere.
Navigation
[0] Message Index
[#] Next page
Go to full version