2-layer  PCB "stackup" - Page 1
Forum section: electronics / beginners

author: pope
author_rank: Frequent Contributor
timestamp: October 05, 2023, 08:33:48 am
content: Hello,I'm working on a 2-layer (THT) PCB for an analog audio design. Traditionally, the stackup is usually all (or most) traces on the top layer and the ground plane on the bottom leyaer.Is there any specific reason for this? I personally prefer having the groundplane on the top layer and the traces on at the bottom. It just looks more neat to me and it's somehow easier to read the screen printing.

author: John Coloccia
author_rank: Super Contributor
timestamp: October 05, 2023, 12:44:02 pm
content: From a purely practical point of view, having the plane on the side of the board you're soldering to makes it easier to drive heat into the plane and get good joints. Of course you'll still want thermal reliefs, but every little bit helps when you're hand soldering.

author: pope
author_rank: Frequent Contributor
timestamp: October 05, 2023, 01:27:45 pm
content: Quote from: John Coloccia on October 05, 2023, 12:44:02 pmThanks for the reply.But usually there are islands and the heat is dissipated from both sides of the PCB, no?I have found quite a lot of statements like the following, but nowhere an explanation of why it should be on the bottom.In a two-layer PCB, design rules indicate this plane should be on the bottom layer, with signal traces and electronic parts on the upper layer.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 05, 2023, 01:29:32 pm
content: Quite obviously it makes no difference, unless you have some super weird special corner case where your PCB has to act as a shield, i.e., the PCB is doubling as one of the walls of the box, then you would want the outside grounded.Quote from: pope on October 05, 2023, 01:27:45 pmAs a rule of thumb, simply ignore all "advice" which seemingly makes no sense and comes with no explanation whatsoever. Illogical statements require strong evidence and clear explanations.Besides, I don't think there is common convention. It can be on either side, both styles can be widely seen in use.

author: pope
author_rank: Frequent Contributor
timestamp: October 05, 2023, 01:54:04 pm
content: The reason I'm asking is because I think that there must be a reasonFor example on the altium site I found the following:EMI/EMC - Placing a ground plane below signals reduces their inductive susceptibility to EMI. In other words, it helps suppress crosstalk from inside the board and noise induced from sources outside the board.Placing a ground plane on the bottom layer of a two-layer PCB provides noise reduction; it reduces the loop area seen by signals.But still, I don't understand why this won't happen if the ground plane is on top. Is it some sort of a requirement from IPC for example?

author: Siwastaja
author_rank: Super Contributor
timestamp: October 05, 2023, 01:58:25 pm
content: I think it's just a language/communication issue. What they actuallymeanto say is "the other side", but they say "bottom side" because they arethinkingabout some example case where traces happen to be at top, and fail to communicate that. People talk illogically like that, and especially if you happen to have any mildly autistic traits like many of us do, such implicit assumptions are hard to see.Replace "bottom" by "opposite" and now the text suddenly starts making sense - they are simply making a point abouthaving a ground plane at all(instead of long ground traces like on a 1-sided PCB).

author: pope
author_rank: Frequent Contributor
timestamp: October 05, 2023, 02:06:00 pm
content: OK I see. Thanks Siwastaja

author: sparkydog
author_rank: Regular Contributor
timestamp: October 05, 2023, 09:27:43 pm
content: Personally, I am a fan of traces on the bottom, ground on top, because it makes the traces easier to visually inspect when the board is covered in components.YMMV. 🤷

author: John Coloccia
author_rank: Super Contributor
timestamp: October 06, 2023, 12:02:29 pm
content: Quote from: pope on October 05, 2023, 01:27:45 pmThat's true, but it's still easier to hand solder through hole when you're heating the side of the board with the most copper, thermal relief or not. Easier to get the solder to flow through to the other side.I have a JBC solder station, and a Hakko desolder station, so it's easy for me regardless...But that's the one practical consideration I can think of for a 2 sided PCB.

author: pope
author_rank: Frequent Contributor
timestamp: October 06, 2023, 12:31:25 pm
content: Quote from: John Coloccia on October 06, 2023, 12:02:29 pmThanks, that's a valid point. Perhaps another argument would be that it's easier to troubleshoot if most traces are on top and the board is attached to the chassis. But, other than these two reasons I can't really see the benefit of having the groundplane on top.

author: tooki
author_rank: Super Contributor
timestamp: October 06, 2023, 01:04:42 pm
content: Quote from: pope on October 06, 2023, 12:31:25 pmPlease fix your quoting. You’ve added your text within it, so we can’t tell what is and isn’t the quoted text and what’s yours.

author: pope
author_rank: Frequent Contributor
timestamp: October 06, 2023, 02:08:52 pm
content: fixed