Possible Flux Corrosion? - Page 1
Forum section: electronics / projects

author: MildInductor
author_rank: Regular Contributor
timestamp: December 20, 2024, 07:37:13 am
content: Hi,I have several SMD breakout boards which I soldered a few months ago. Upon going to look at them today I noticed significant corrosion on the joints. I used standard lead free solder and flux to rework them. I can't exactly remember which model of flux I used a few months ago. However, I always thoroughly cleaned the boards with isopropanol alcohol approximately 30 minutes after soldering such that they looked to have no flux residue left on them. I am fairly sure the flux is the culprit here as I have some other THT joints that were soldered without flux, and they do not have any corrosion.Any ideas what I can do to rectify this now and prevent this in the future?Thinking about it I am fairly sure the flux was from Chip Quik or MG Chemicals. I am not sure which model it was though.

author: inse
author_rank: Super Contributor
timestamp: December 20, 2024, 08:25:51 am
content: At work we recently identified flux pens with water based flux that caused corrosion on PCBs, even eating through the gold plating.I read the datasheet and it said to wash it off with water, maybe isoprop alc does not clean it sufficiently…We threw away those pens and only kept the no-clean rosin based ones.

author: MildInductor
author_rank: Regular Contributor
timestamp: December 20, 2024, 09:41:34 am
content: Ok that's interesting to hear. Luckily only a few boards out of my collection that I soldered a few months ago have seemingly corroded. I'll make sure to use a no-clean rosin based flux in future. Re washing the board, would one use distilled water and perhaps an ultrasonic cleaner? Does the IC not have issues being submerged in distilled water?

author: inse
author_rank: Super Contributor
timestamp: December 20, 2024, 10:43:04 am
content: No issue for ICs but for relays and switches for example

author: jpanhalt
author_rank: Super Contributor
timestamp: December 20, 2024, 10:46:03 am
content: Kester makes water-based flux removers. I followed its formula and make my own using ZEP-brand heavy duty floor stripper. (ZEP told me it is not distributed in Australia.) The active ingredient is butyl cellosolve (2-butoxyethanol and other names) plus a little ethanolamine. That's what I use in an ultrasonic and rinse with tap water followed by deionized/distilled water in an ultrasonic.It's quick in my old Bransonic (about 1 minute for cleaning and final wash each).The distribution of discoloration you show reminded me of what I saw with "white residue" after cleaning with ethanol/acetone. It was mainly in crevices in and around fine pins. You could only see it easily under a microscope. The water-based cleaner removed every bit of that residue (attachment). Kester studied white residue and stated you need a "saponifier" to remove it. That may be why ethanol amine is added.https://www.kester.com/Portals/0/Documents/FAQs/White_Residue.pdfEDIT: Added DSCN1447 (white residue) and DSCN1467 (clean)

author: Siwastaja
author_rank: Super Contributor
timestamp: December 20, 2024, 07:40:51 pm
content: For prototyping or hobby, just get no-clean flux. Washing is PITA and also not trivial to get right (residues left behind in wrong places, or damage to non-washable parts). For commercial manufacturing they are used to do it and know the tricks and have an optimized process for it, but in lab scale it's waste of time.Plus, to wash, you need to know exactly what the flux was to be able to get exactly the right washing agent for it. Some are hard to find in small quantities - easier to just buy new flux which doesn't require washing.

author: wraper
author_rank: Unknown
timestamp: December 20, 2024, 07:47:54 pm
content: Quote from: inse on December 20, 2024, 08:25:51 amIt's like trying dissolving table salt with IPA.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 20, 2024, 08:41:19 pm
content: "One test is worth a thousand expert opinions." That axiom is from experience. Try Kester 5768 flux remover or its formula equivalent as described.Look for any cleaner with 2-butoxyethanol or equivalent names (https://en.wikipedia.org/wiki/2-Butoxyethanol) in household cleaners. Once you smell it, you will recognize the oder. I wouldn't call it sweet, but it is not unpleasant and is a little alcoholic. It probably will contain ethanolamine, but any amine will work, even ammonia or a little sodium hydroxide. (Those latter comments are based on theory, not experience.) Dilute in water to about 10% final concentration of the butoxyethanol.I was a doubter and was amazed the first time I tried it. After that, I only use an ethanol/acetone mixture for spot cleaning. NB: Kester markets it as a cleaner for rosin fluxes. I use Kester rosin fluxes. Given that 5768 is 90% water, it may well work with water washable fluxes. (They also have rosin in them.)

author: tooki
author_rank: Super Contributor
timestamp: December 29, 2024, 01:27:50 pm
content: Quote from: Siwastaja on December 20, 2024, 07:40:51 pmJust a reminder to all that “no clean” flux is only guaranteed safe to leave on if it has been fully heated to soldering temperature. This is guaranteed when using only the flux core in solder wire, or when successfully reflow soldering in an oven. But it is NOT guaranteed when using external flux (=liquid or paste/gel/tacky) with a soldering iron or hot air. Some of the flux may flow away before reaching full temperature, leaving it in an activated state.So if you use any external no-clean flux and don’t do a whole-board reflow in an oven, then the flux must be removed. And many no-clean fluxes, especially those for lead-free, are not optimized for ease of cleaning and can be very difficult to remove thoroughly.Traditional rosin fluxes tend to be much easier to clean, so I recommend hobbyists stick with that. Many rosin fluxes are just as safe to leave on as no-clean fluxes, they’re just more visible.

author: shapirus
author_rank: Super Contributor
timestamp: December 29, 2024, 01:57:42 pm
content: Quote from: MildInductor on December 20, 2024, 07:37:13 amYou may find it useful to test your fluxes on a bare copper board (and also on a tinned portion of it).There's also more info and discussions on parasitic corrosion and conductivity inhttps://www.eevblog.com/forum/chat/good-soldering-flux/.

author: eb4fbz
author_rank: Regular Contributor
timestamp: December 31, 2024, 09:55:29 am
content: No-clean flux should not be cleaned with IPA. It will leave acidic salts know as “white residue” all over the board that will corrode it over time. No-clean flux is not meant to be cleaned, other wise it’s a PITA.The lead-free solder wire you used probably had no-clean flux core.

author: tooki
author_rank: Super Contributor
timestamp: December 31, 2024, 10:02:22 am
content: I’ll add that an ultrasonic cleaner is a game changer for PCB cleaning.Even tough fluxes come off with ease and a suitable cleaning medium.I’ve been experimenting with the water-washable no-clean fluxes a few manufacturers offer, and initial results are quite promising — these just need hot water. Follow with a distilled water rinse, optionally also a final rinse in IPA or ethanol. Blow dry with compressed air.