Electrical and Computer Engineering

864 readers

1 users here now

Electrical and computer engineering (ECE) community, for professionals and learners. Discuss ECE related topics here, for instance digital design, signal processing, circuit analysis, electromagnetics, microelectronics, power electronics, RF electronics, etc.

founded 1 year ago

MODERATORS

[email protected]

[Youtube] Rick Hartley How to Achieve Proper Grounding (2 hour talk) (www.youtube.com)

submitted 1 year ago by [email protected] to c/[email protected]

2 comments fedilink hide all child comments

cross-posted from: https://lemmy.world/post/5751732

I posted this to someone else's Microcontroller Lemmy, but I want to see how many people at Lemmy.world might be interested in this kind of material too

In my most recent "Beginner Series" post, I classified skills from Tier0 through Tier4. This Tier4-level talk is about how to think of PCB-layout at the most complex levels, thinking about the precise forms of electricity and why-and-how it creates EMI fields, almost like an antenna at times. (Or perhaps: more like a capacitor when these waves travel across a PCB).

This video covers proper "grounding", or perhaps more accurately, proper "reference planes" where the electrical field between signal-and-return current can be defined. Thinking in terms of both signal-current and return-current minimizes the EMI (aka: antenna-like radiation) from coming off your PCBs. This is more of a problem of high-speed circuits and therefore I rate it as "Tier 4".

you are viewing a single comment's thread
view the rest of the comments

[–] [email protected] 2 points 1 year ago* (last edited 1 year ago)

I'm shocked at how bad the industry standard 4-layer signal-top/ground/power/signal-bottom stackup is with this new paradigm of thinking.

Even if the power-plane is solid (unlikely: modern designs often need 2 or 3 power rails, and thus the power-plane is often split).... but if power was a solid reference plane, we still have an issue with signals traversing signal-top to signal-bottom and vice versa. The return-path of signal-top traverses the ground plane, while the return-path of signal-bottom traverses the power-plane.

On a 4-layer stackup, ground-and-power are split by the "core", often 1mm or ~39 mils. That's too far apart to have any significant amount of capacitance, so ground-and-power planes are effectively cutoff, meaning the return-paths are poorly defined and will bounce and/or radiate out of your board, looking for a way to return.

This video recommends signal-top/ground/ground/signal-bottom for a reason (and therefore, routing power / not having any power-planes), and has the data / analysis to backup why this is the appropriate stackup. Taking this approach means that 4-layer boards have far less room than we might expect, at least if we're trying to have good EMI. Not only that, but you'll need 2 vias whenever you traverse from signal-top to signal-bottom, because the return paths need to travel from ground-top to ground-bottom as well (!!!!).

It seems like 4-layer boards are barely usable with this new paradigm of thinking. 2-layer boards are nearly impossible (you need to route lots of grounds/return paths on the top-layer, because the 60mils from top-to-bottom means that the bottom ground-plane is barely usable at all).