Little copper squares on a PCB - Page 1
Forum section: electronics / beginners

author: Fantasma25
author_rank: Regular Contributor
timestamp: October 19, 2015, 05:29:36 pm
content: Hello! I was looking at this PCB (http://blogs.synopsys.com/breakingthethreelaws/files/2013/05/connectors.jpg) and I noticed that it has a lot of little copper squares covered with solder mask. My theory is that they are there for some PCB mechanical reason (something related to heat?), but I'm not sure. Has anybody ever had to use them?Thanks!

author: Simon
author_rank: Unknown
timestamp: October 19, 2015, 05:37:31 pm
content: I don't think they have anything to do with heat sinking. They look more like a copper pour. Copper pours can be done as a complete sheet or in various patterns. Some older boards have a diamond shaped pattern. If they work for heat transfer they would be in larger areas rather than small squares.A copper pour will also avoid using up too much etching chemical perhaps in the past they felt that a complete seat would not come out properly so did patterns.

author: djQUAN
author_rank: Frequent Contributor
timestamp: October 19, 2015, 06:13:00 pm
content: They are used to even out the copper vs no copper area on both sides of the PCB so that during reflow, the thermal expansion of both sides are equal and does not cause the PCB to warp.

author: Gyro
author_rank: Super Contributor
timestamp: October 19, 2015, 06:14:27 pm
content: It's called auto-thieving. Its purpose is to improve the consistency of plating across the board.Edit: At least the non-masked ones are. Yes the masked ones help with thermal balance during processing.Another Edit: I believe they also improve consistency of etching - nothing like covering all the bases

author: Falcon69
author_rank: Super Contributor
timestamp: October 19, 2015, 07:27:53 pm
content: another thing as well I've noticed with my own boards....Having more copper on one layer, tends to make my board warped. So maybe in this situation, they tried to balance the amount of copper on each side. But, I have really only noticed this happening with my boards when I do a solid layer on one side, none on the other.It's like having a sheet of 1/4" plywood. Then gluing Laminate to one side. It warps like crazy. But when you glue Laminate on both sides, it stays flat. The surface tension of the glue/laminate pulls in both directions when laminate on both sides, making the piece stay flat.

author: free_electron
author_rank: Super Contributor
timestamp: October 19, 2015, 08:01:09 pm
content: copper thieving structures.this is done to prevent the board from warping during processing. these structures are staggered between layers.

author: lewis
author_rank: Frequent Contributor
timestamp: October 19, 2015, 08:08:25 pm
content: There's some more info here:http://www.ee-training.dk/announcement/copper-thieving-confusion.htm

author: Simon
author_rank: Unknown
timestamp: October 19, 2015, 08:12:43 pm
content: so it's about plating and not board warping. Would never have guessed.

author: Fantasma25
author_rank: Regular Contributor
timestamp: October 19, 2015, 09:52:07 pm
content: Quote from: lewis on October 19, 2015, 08:08:25 pmWow, that's interesting! So the plating is done before they apply the solder mask? Or does the desired effect still holds even after the solder mask is applied?

author: tooki
author_rank: Super Contributor
timestamp: October 20, 2015, 02:41:48 am
content: Well I think the plating in question here is the copper of the traces, so yeah, it's done before solder mask is applied. Otherwise you'd have thick pads but uselessly thin traces. (As opposed to gold plating. Not sure when it's applied.)

author: jitter
author_rank: Frequent Contributor
timestamp: October 20, 2015, 04:49:32 am
content: Quote from: Fantasma25 on October 19, 2015, 09:52:07 pmYes because the desired effect is only needed as long as the plating process of the pcb takes place. After that they don't serve any function anymore (they are copper thieves, not solder thieves).So it's not meant for solving thermal issues nor does it prevent board warping.The warping thing I can attest to, once I was testing a product on a rather long board that inevitably hard warped slightly. Somehow two different batches of pcbs were used, both from different manufacturers. One of them had the little squares on them, the other did not. I didn't notice any difference with board warping between the two batches.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 20, 2015, 10:09:51 pm
content: Quote from: blueskull on October 20, 2015, 04:56:20 amI always skewer those with at least one via. Still not best for impedances, but in my opinion, floating anything should be an OCD thing for anyone doing layout! And besides, more ground is more betterer.Then I only remove very small (usually < 4mm?) blobs, because who cares at that point.Tim

author: Pack34
author_rank: Frequent Contributor
timestamp: October 21, 2015, 01:59:17 pm
content: What's with those connectors? Looks like they poured something on them?

author: cowana
author_rank: Frequent Contributor
timestamp: October 21, 2015, 02:42:33 pm
content: Quote from: Pack34 on October 21, 2015, 01:59:17 pmPick and place pads, so the connectors can be picked up by a vacuum head before placing on the board.They'll be bits of plastic attached with a very weak glue.