Fills of unused space on PCBs - Page 1
Forum section: electronics / general

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: April 09, 2020, 06:24:08 am
content: I was once told that it is a good idea to just fill large empty pieces of PCB space with copper pours (and usually connect them to ground because why not, but that is a separate discussion). The reason I was given is that during etching, etchant is used up in proportion to how much needs etching - and since PCBs start out as solid pieces of copper and then have everything that is not supposed to be copper etched off, having large patches of empty space without copper is wasteful. Hence, manufacturers would appreciate it if you fill up that empty space with copper.Now, assuming that filling it with copper has no negative effects on performance, is this true? It is a good idea to just flood everything with a poly pour?

author: ANTALIFE
author_rank: Frequent Contributor
timestamp: April 09, 2020, 06:38:36 am
content: Back in the day PCB fab houses would have been picky about copper etching, etchant traps... These days they don't really care as technology has improved to the point where it's no longer a worryAlso in most cases what you said is correct, it's better to do a big copper pour and connect to GND. But this is only true up to a point, for example you would not do this if your circuit was HF

author: AndyC_772
author_rank: Super Contributor
timestamp: April 09, 2020, 06:43:11 am
content: What are these "large empty pieces of PCB space" you speak of? (Can't remember the last time I had that luxury!)

author: Ian.M
author_rank: Super Contributor
timestamp: April 09, 2020, 06:55:01 am
content: Most PCB houses are going to be using the acid copper chloride process, which is a regeneratable etchant, and recovering the copper to comply with environmental regs, (and because of the high price of copper) so there is no longer any benefit in leaving unconnected copper on your board. Its a different matter if you are DIY etching with ferric chloride.

author: jfiresto
author_rank: Frequent Contributor
timestamp: April 09, 2020, 07:57:40 am
content: Can copper imbalance, having much more copper on one side than the other, still cause warping?

author: AndyC_772
author_rank: Super Contributor
timestamp: April 09, 2020, 08:05:43 am
content: It's a good idea to ensure your stack-up is balanced. So, for example, if you're making a 6 layer board, it would be normal to use layers 2 and 5 for power and ground, with 3 & 4 either both used as planes or both used for tracking. If you need 3 power planes, it would be a good idea to flood the 'odd' tracking layer with GND in order to ensure the amount of copper is evenly distributed throughout the board.The main reason to put copper in unused areas of the board is to help ensure the electroplating process (which is used to make through vias and to increase the copper thickness on outer layers) is uniform. Some board manufacturers can use a peelable mask to add copper where they need it and then remove it afterwards, so you're never even aware they've made the board this way.

author: Harjit
author_rank: Regular Contributor
timestamp: April 16, 2020, 01:07:39 am
content: I usually put down through hole and SMT pads so that if I run into a problem, I can solder a few parts, wire them up using wire-wrap wire and hopefully, keep going.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 16, 2020, 01:29:17 am
content: Always found the arguments amusing, because etchant is cheap and copper is expensive.Shouldn't that mean fabs prefer more etch, because they get more money back (or less cost spent, at least) when recycling etchant?Or maybe it's the other way around. Curiously, no one ever gives budgetary numbers. (And even if they did, they would only be true for the one case they came from. And they'd probably still be made-up numbers.)The reality is this:Copper foil is cheap. Unless you're making more than ten thousand of them, you won't even begin to feel the cost difference of 4 vs. 2 layer boards (given a layout optimized for either process, and assuming the mechanical outline can support either one). Let alone of optional silkscreen or soldermask layers, let alone punched phenolic boards, or 1 vs. 1/2 oz foil, or whether it's etched a lot or a little.As for warpage, as far as I know that's intrinsic to the laminate and isn't going away any time soon. But, also isn't much of a problem until you get into large leadless packages (where the part might not sit flat, leading to solder defects).Tim

author: OwO
author_rank: Super Contributor
timestamp: April 16, 2020, 05:52:53 am
content: Oh there are plenty of reason you want your board to be flat. Such as mounting in a CNC machined enclosure/shield caves. Yes the screws will bend the PCB to conform to the enclosure, but that means stress on all solder joints.