Best practice for routing signals to avoid splitting grounds - Page 1
Forum section: electronics / beginners

author: amaschas
author_rank: Regular Contributor
timestamp: August 06, 2022, 04:34:25 am
content: I recently received feedback on a layout for a 4-layer board (which contains several switching power supplies) that has me questioning some of the practices I have been following regarding the routing of signals. I was originally taught to keep as much of a given signal trace on the top copper layer as I could, and to only dip down onto the signal layer when necessary. While this resulted in the ground plane being fairly broken up on the top copper layer, my sense was that as long as I had vias that connected to the internal ground plane in locations that would help reduce ground loop area, that this wasn't really a problem. I also additionally add a ground fill to the signal layer, so there is a fair amount of ground plane on this particular board. The feedback I received, however, indicated that it would be much better to maintain an unbroken ground plane as much as possible, (on boards with switching power supplies particularly), and if I needed to route most of my signals on the internal signal layer, then that was fine. I'm wondering what approach people here prefer.

author: fourtytwo42
author_rank: Super Contributor
timestamp: August 06, 2022, 05:56:23 pm
content: Unfortunately you know what your calling the "signal layer" and what the other two layers do but nobody here does as you didn't bother to tell us!

author: amaschas
author_rank: Regular Contributor
timestamp: August 06, 2022, 06:40:15 pm
content: Quote from: fourtytwo42 on August 06, 2022, 05:56:23 pmAh yes, fair enough. Let's assume we're talking about a 4-layer board, with a top copper layer, an inner ground layer, an inner power layer, and a bottom signal layer. Both the top and bottom layers have ground fills as well. Components are only placed on the top layer due to manufacturer restrictions.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: August 06, 2022, 10:04:13 pm
content: Show some images. It's okay to have holes in your planes, but you need to make sure some copper can get between these holes. The Howard Johnson "Black Magic" book has an excellent chapter or two about this. There are also some video lectures by him onhttps://www.oreilly.com/.It's more than worth a month's subscription to watch these.You don't really want you ground planes extended to your signal layers unless you have a good reason. One reason would be to help with cooling. If you do this then you need to stich the planes together every 100 mm. Just avoid it most of the time.

author: ejeffrey
author_rank: Super Contributor
timestamp: August 06, 2022, 10:54:47 pm
content: I'd drop the ground fill from the outer layers. It is normally not necessary or helpful.

author: Terry Bites
author_rank: Super Contributor
timestamp: August 11, 2022, 05:17:53 pm
content: Think about ways to compartmentalise each converter sub-system. In fact all sub-systems! Star ground using wide tracks can give better perfomance. Current takes the path of least impedance but flows all over the place as lesser currents. In high current circuits these lesser currents can be significant, particularly at high switching speeds. Its a good idea to treat the ground and power rails as performing the same function. Which they are. Power is referrenced to ground and vice versa. Very thoughtful ground is pointless if the power routing is all over the place.Gaps in the groundplane can and will radiate EMI. This is not good for the radio environment or your sensitive areas.Some sage advice and in this thread.https://www.eevblog.com/forum/projects/ground-plane-vs-star-groundpower/

author: analityk
author_rank: Regular Contributor
timestamp: August 12, 2022, 10:08:03 am
content: You should watch Robert Feranec talking with Eric Bogatin about stackup, ground layers and how to avoid excessive emi. It is on YT free, you must not pay for this knowledge.Main goal is not breaking return path, firstly you should know how to current flow through wires on PCB. One solid plane should not solve all problems.Also you have to know there is better and weaker smps chips, chokes, capacitors. SMPS have not forgive nothing but sometimes other chips on this same PCB can work properly. You have to have some lucky.

author: amaschas
author_rank: Regular Contributor
timestamp: August 18, 2022, 04:45:06 am
content: Thanks all, I've read through all of the recommendations, and I'm working my way through the videos. All very helpful!