PCB trace grid on DC drive

[Eze Celsed]

Hi everyone, first post here.



This PCB caught my eye the other day since I had never seen what looks like a grid of copper traces on the outermost layer of the board. This was the controller board for a NIDEC brand DC motor drive.

Would anyone happen to know what the grid's purpose is? I would guess it's either for EMI control or power dissipation, but if anyone has had experience with this I would love to hear an explanation.

Thanks!
-Eze

[T3sl4co1l]

It's slightly worse for EMI, since the openings allow some field to pass.  How much depends on requirements, frequency, and how traces are routed underneath it.  Conversely, it tends not to be a good idea where

I would guess it's for copper balance, to avoid warping the board.  Copper has different expansion rate from FR-4, and copper density should match between top and bottom layers.  Filling an otherwise-underutilized layer can prevent warpage.

It could also be to provide a venting path for trapped gasses; FR-4 absorbs some moisture in storage, and can blister and delaminate on rapid heating.  This doesn't seem to be a precaution used much these days, but I've seen mesh planes in older boards before, maybe it used to be more of an issue.

Tim

[EPAIII]

I have seen similar grids on boards. As far as I know it is just another way of providing a ground plane. Nothing more or less, just a personal preference of the person who designed the board.

[hans]

 Its before my era, but I heard some stories of very early CAD software having trouble with fully covered planes. A hatched pattern was perhaps the way to go back then. Anyone that can confirm or bust that rumor for me?

[T3sl4co1l]

I've certainly seen some files with a hell of a lot of traces filling space. Some tools do that still (more for Gerber output, where, I guess that's just whatever), but my main experience was with PADS, uh, 13 or so I think?

Tim

[tooki]

https://resources.altium.com/p/history-and-use-cross-hatched-planes

[Eze Celsed]

Thanks for all your input!

-Eze

[twospoons]

Copper plane hatching was also recommended to improve etching back the the old days when that board was made.  The idea being to keep the etchant concentration as consistent as possible across the pcb to avoid over or under etching in different areas.
No longer seems to be a problem with current PCB fabs.

[EPAIII]

Thanks! I just learned more about cross hatch planes than I ever wanted to know. Good reference.
 

https://resources.altium.com/p/history-and-use-cross-hatched-planes