Trying to develop best power plane practices - Page 1
Forum section: electronics / beginners

author: LoveLaika
author_rank: Frequent Contributor
timestamp: June 15, 2023, 06:04:29 pm
content: I'm trying to better understand power planes and how to best use them. For most of my circuits, I typically route power traces rather than dedicate a whole plane to power, but I want to learn how to start working with power planes to improve my understanding of them. I just don't really understand how people use them.I see a lot of stack-ups have a dedicated power plane (say in 4-layer boards), or at least mix signal and power on the same plane for the 2-layer boards. For my 2-layer projects, I more or less typically make both top and bottom pours tied to ground, and then I route signal/power on the same or separate layers, depending on the application. The same kind of goes with my 4-layer boards. I try to avoid routing power and signal traces on the same plane. When you dedicate a plane solely for power, do you take it as to tie the entire plane to a power net, or do you leave that layer as unconnected (or to ground) and only route power traces along that plane? What if you had two power nets, such as the case for many op-amps? What if you had two independent copper pours (tied to their respective power nets) on the same layer? That way, you could potentially power the op-amps through vias (also depends on their placement). I know these all highly depend on the application, but I just want to get some best practices in. I sometimes worry that I'm not building PCBs correctly even though my circuits work.

author: LoveLaika
author_rank: Frequent Contributor
timestamp: June 15, 2023, 06:27:58 pm
content: Quote from: karpouzi9 on June 15, 2023, 06:16:35 pmThanks for replying.Q1: I often use op-amps which require split power supplies, so rather than tie the entire plane to one net, I just use thick traces to route power respectively. Sometimes, I have to route signals internally when I can't have them all on one layer, so I don't really dedicate a plane to power solely for that reason to allow signals to be routed internally. I thought a power plane would affect that.Q2: I don't understand this. Say you route the traces. Then, you expand the traces until the two different nets meet as you say. That's just simply using traces. Why not have planes in the first place rather than traces, at least when you can? Component placement might make using split planes impossible, as I've experienced, so I would just use wide, internal traces on separate layers.

author: LoveLaika
author_rank: Frequent Contributor
timestamp: June 15, 2023, 07:03:56 pm
content: Thanks again for replying so quickly. If I may add on:QuoteDoes it really sound like that? I was talking about 4-layer boards. For 2-layers, I don't bother with power planes. I just use traces. In my last 4-layer project, while I tied each plane to ground for ease of access, I tried to keep my routing as followed: (signal)(power, +5V trace)(power, -5V trace)(signal/ground). See, I (try to) dedicate each layer to a power trace as best as I can, and I use vias to stitch the ground planes together. Although, signal traces can't all be on a single layer, so I had to use other layers. This breaks the plane. It's hard to get a solid ground pour that's unbroken when you have lots of vias going back/forth.With what you said, dedicating inner layers to power, it would be simpler, but with vias connecting between other nets aside from power, that would break the plane. Is that a big issue (it seems to be when it comes to ground planes, but perhaps not so for power planes).QuoteWhat do you mean by recording the expanded planes? I typically set components and then route them, then adjust them every five minutes to accommodate for something. Whenever I see the pour broken at a point, I move around stuff to make it fill in, etc. All auto adjusting on the go.QuoteYeah, I suppose one can have oddly shaped planes. I only use SMT components with vias to route power traces appropriately. That way, one thick long trace can reach all necessary components. In a minuscule sort of sense, that could be seen as a plane by the components, could it?

author: LoveLaika
author_rank: Frequent Contributor
timestamp: June 16, 2023, 01:22:47 pm
content: Actually, if I may, I whipped up a dummy project to see how to use power planes as an example, and given what you said, I was wondering if this was the right way to go about it.The way I went about the stack-up is: (Signal, Pour unconnected)(Power, +5V)(Power, -5V)(Ground Pour). Hopefully the pictures help. It's not super complicated for practice.I left the top copper unconnected to any net, so I had to use a ground via to tie the op-amp input to ground. As for the inner layers, you can see how I dedicated each inner layer to a power net. See how it fills around their respective connected net? Ideally, I could have had them both on the same plane as different zones, but given the orientation of the op-amps, their power pins weren't aligned with one another. I would have had to make some odd zones, so it seemed easier to have them on separate layers (I did this on purpose).As for the bottom pour, it's tied to ground. I only put capacitors down there, so it's only broken by the pad connected to power and the input/output through-holes from the connectors.From all this, is this the right practice of power plane usage? What can I do to improve, more or less? Notice how my inner layer copper pours do not fill out the entire board. Should I expand my power planes to fill the entire board rather than just one small area?

author: LoveLaika
author_rank: Frequent Contributor
timestamp: June 22, 2023, 01:58:47 pm
content: Quote from: karpouzi9 on June 17, 2023, 05:49:57 amWell, you mentioned how the top layer was meant for signals. I took that to also mean that the top layer copper pour would be unconnected to anything. Normally, I would connect it to ground.Thanks for the note. That would be something to consider in my next designs.