Cleaning Rain Water from Bare PCBs  - Page 1
Forum section: electronics / general

author: xbst_
author_rank: Contributor
timestamp: August 14, 2025, 02:53:52 pm
content: I recently got a batch of bare PCBs delivered. Unfortunately it was raining pretty heavily that day, and when the UPS guy dropped the box off, the box was so wet, half the box was disintegrated. The PCBs were in plastic packaging but looks like some water made leaked in.I tried cleaning them with water, 99% IPA, 99% acetone, spray flux cleaner, ultrasonic cleaner filled with flux cleaner and anything else I can think of, but no matter what, solder doesn't flow properly on all pads during reflow. There are also some hand soldered parts, and they take a long time and a ton of flux to barely solder.The prototype batch of these PCBs flowed fine, and very little changed between them and this batch, so it must be the rain water.Anything else I can try to clean these? They're ENIG if it matters.

author: Kean
author_rank: Unknown
timestamp: August 14, 2025, 04:02:45 pm
content: Did you try baking them to dry them out?If not then I'd suggest doing that at 100°C in an oven for about 4-6 hours.

author: Accu-Sembly
author_rank: Contributor
timestamp: August 14, 2025, 04:40:01 pm
content: These absolutely need to be baked or you are going to have serious issues during reflow.Based on what you described, the boards are "clean" by now, but the pads have a thin layer of oxidation on them. Not sure what your volume is like, but an old school simple solution is to rub a pencil eraser on the pads before soldering.

author: jayx
author_rank: Regular Contributor
timestamp: August 14, 2025, 07:28:24 pm
content: That's strange. You should bake PCBs, but for other reason. Rain water shouldn't affect gold, it doesn't oxidize.

author: thm_w
author_rank: Super Contributor
timestamp: August 14, 2025, 10:00:05 pm
content: Visually is there any difference between the old and new PCBs?If none of the above works could try a fine abrasive like 2000 grit sandpaper, see if it makes any difference to solderability.

author: xbst_
author_rank: Contributor
timestamp: August 15, 2025, 12:47:37 pm
content: Quote from: Kean on August 14, 2025, 04:02:45 pmI tried wiping them, then putting them in a box with silica overnight. I'll try that too.

author: xbst_
author_rank: Contributor
timestamp: August 15, 2025, 12:48:50 pm
content: Quote from: Accu-Sembly on August 14, 2025, 04:40:01 pmI don't have a pencil eraser but I can get some. The boards are ENIG, how can they oxidize though?

author: xbst_
author_rank: Contributor
timestamp: August 15, 2025, 12:50:59 pm
content: Quote from: thm_w on August 14, 2025, 10:00:05 pmThey look weird, especially pads near the board edges. There's definitely something wrong with them.

author: Ian.M
author_rank: Super Contributor
timestamp: August 15, 2025, 01:18:14 pm
content: Rain water can be far from pure. In some locations known for their air pollution, it typically has high levels of acids and suspended and dissolved particulates. However your boards were wetted with soggy cardboard juice, which may contain sodium silicate, starches and gums, and traces of residual acids or alkalis from the pulp processing.The gold layer in typical ENIG finishes is so thin that it can be microporous, allowing the underlying nickel to oxidise or corrode.What to do depends on exactly how the pads are failing to wet. If the gold layer is dissolving in the solder exposing dark tarnished nickel underneath, the boards are probably unsalvageable. If the gold is simply not wetting, try abrasive cleaning with an eraser or rubber polishing pad, or even metal polish, followed by extremely thorough board washing and bakeout.It may be worth raising the matter with your supplier as it seems UPS may have failed on the 'last leg'. OTOH if it was dry at the time of delivery but rained later, and your usual delivery location left them sitting in a puddle before you could get to them, that's down to you!

author: xbst_
author_rank: Contributor
timestamp: August 15, 2025, 01:28:25 pm
content: Quote from: Ian.M on August 15, 2025, 01:18:14 pmThe rain water probably isn't great here. I brought it inside immediately. It wasn't raining at the time of delivery, but it rained earlier and I guess they got wet then.It's 2u ENIG in this case. Gold seems to survive soldering. I'll try something abrasive.

author: jpanhalt
author_rank: Super Contributor
timestamp: August 15, 2025, 04:05:52 pm
content: That looks like a typical UPS delivery in my area.

author: thm_w
author_rank: Super Contributor
timestamp: August 15, 2025, 10:04:29 pm
content: Can't tell if thats a proper box or just brown paper wrapping, it doesn't look very strong.Normally PCBs are vacuum packed, so even if the box gets dropped in water the PCB will be fine if the plastic layer is not torn. In this case I guess the impact tore the plastic.

author: xbst_
author_rank: Contributor
timestamp: August 18, 2025, 10:43:26 am
content: Quote from: thm_w on August 15, 2025, 10:04:29 pmIt was a proper box and the PCBs were vacuum packed but water leaked inside.

author: xbst_
author_rank: Contributor
timestamp: August 18, 2025, 10:50:04 am
content: I tried magic eraser, pencil eraser and aluminum polish. Only aluminum polish seemed to help, but I have to grind it down to the nickel layer for solder paste to flow well. Takes a long time and a lot of polish, and still doesn't help enough with the through hole parts. It obviously also makes screw hole pads look atrocious.I contacted the supplier and they're trying to weasel out of responsibility like usual. They'll probably only give me a tiny coupon for it. I really wish we had affordable PCB houses in the US.It sucks but I think I'll have to eat this cost. $1000 of bare PCBs wasted...

author: Bud
author_rank: Super Contributor
timestamp: August 18, 2025, 12:12:00 pm
content: What PCB company was it?

author: Bud
author_rank: Super Contributor
timestamp: August 18, 2025, 12:26:01 pm
content: When you say reflow, do you mean reflowing a board in the oven or just hand soldering? Try to reflow in the oven, maybe flux/paste will activate better. Also try a different type of paste/solder.

author: xbst_
author_rank: Contributor
timestamp: August 18, 2025, 12:30:14 pm
content: Quote from: Bud on August 18, 2025, 12:26:01 pmOven for SMD. I'm using a Neoden IN6. Through hole ones are hand soldered though not wave soldered.

author: Matt-Brown
author_rank: Regular Contributor
timestamp: August 18, 2025, 04:39:10 pm
content: It is not rainwater, or any other water that caused the change to the ENIG finish. It is the processes the board house used (probably used mask that was still wet when they did the final plating. We have had 2 batches where we just touched a large pad with a finger and it reacted (just like your pictures). I would send a picture to the board house of the issue as they have the order of processes wrong.

author: Accu-Sembly
author_rank: Contributor
timestamp: August 18, 2025, 07:59:52 pm
content: That sucks. What's the most aggressive flux you have? Do you have the ability to effectively clean a high reactivity water-soluble flux?

author: xbst_
author_rank: Contributor
timestamp: August 18, 2025, 11:27:55 pm
content: Quote from: Accu-Sembly on August 18, 2025, 07:59:52 pmI tried using NC191 flux, heated for a while and cleaned, then assembled. Helped a bit, but not enough. I can try a more aggressive flux if you think there's a chance that'll help. I guess I can clean it in my ultrasonic cleaner.I sorted all the PCBs in this order today. About 80% PCBs in this order are not usable, so I'm willing to try everything I can to save that 80%. These are 6 layer boards, I'd hate to waste $1000 of PCBs.I took more photos of the pads.

author: Accu-Sembly
author_rank: Contributor
timestamp: August 19, 2025, 07:25:22 pm
content: NC191 is an ROL0 flux, so the lowest possible activity level. Using a more active/aggressive flux will definitely help. I can't tell if it would be enough, but it's a relatively low cost process improvement.Chip Quik WS995 is a REH1 flux. Note the cleaning requirements (hot water, at least 60*C).If you can meet the cleaning requirements, I would definitely try this next.