Dead, dumb or dumber copper? - Page 1
Forum section: electronics / projects

author: w3amd
author_rank: Regular Contributor
timestamp: November 10, 2015, 04:45:28 pm
content: In the shown case this through hole pin is shown connected to a ground plane but would have zero current. I would call this dead or dumb copper.Am I correct?

author: dmills
author_rank: Super Contributor
timestamp: November 10, 2015, 04:49:26 pm
content: Dead copper would be the usual term here.Note that if you have such a thing connected to a high speed signal net it can be a problem, because a conductor connected to a signal source at one point has another name "Aerial" especially if it has non trivial electrical length.Regards, Dan.

author: KJDS
author_rank: Super Contributor
timestamp: November 10, 2015, 05:49:24 pm
content: in some ways that's potentially an antenna, and in other ways it's providing a screen between the surrounding pins.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: November 10, 2015, 05:50:51 pm
content: It can also be for mechanical reasons to give strength to the connection to the board and to reduce stress on the other solder joints.It can also be to secure the pin to prevent it from getting loose.Is the pin connected to the PCB ground plane or just that little area?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 10, 2015, 06:13:34 pm
content: Stick...stick your via in it...

author: w3amd
author_rank: Regular Contributor
timestamp: November 11, 2015, 12:59:06 am
content: Quote from: Tomorokoshi on November 10, 2015, 05:50:51 pmYes, along with another layer as well. Apparently they were very concerned with this pin getting loose so they tied it to the same plane on two layers giving the bonus ground loop potential.Does anyone know what IPC spec calls out this kind of thing? You guys could save me about 6 hours of further research.Cheers!

author: homebrew
author_rank: Frequent Contributor
timestamp: November 11, 2015, 07:32:33 am
content: Well, we cannot see the other layers. Hence it is difficult to call it 'dumb'. Why would you assume that no current is flowing there? Just because it is connected only at one end? True for dc but very wrong for ac. You could still have capacitive coupling.Maybe it was just what the ground pour algorithm did ...Maybe the somebody was really worried about his ground plane etc. etc.Is there a specific problem that you address to this piece of copper?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 11, 2015, 12:40:46 pm
content: IPC is primarily concerned with manufacturability, not high speed or EMC.I don't see anything wrong about it.Tim

author: dmills
author_rank: Super Contributor
timestamp: November 11, 2015, 03:47:51 pm
content: Indeed, just a copper snot left over from a pour.Most boards of any complexity have such things, because tweaking the rules to kill them tends to break other things.My point really was that these sorts of things are not ALWAYS benign, not that this one (being on a ground net as it is) was likely to be any sort of issue.Regards, Dan.

author: w3amd
author_rank: Regular Contributor
timestamp: November 15, 2015, 01:26:49 am
content: Agree,Unlikely to cause an issue but could cause an issue. I'm weighting each of these one sided nets. They are potential receiving or transmitting antennas. But what would actually happen would need to be weighted on a case by case basis.JohnW3AMD