How to clean bad flux off a 2-sided board that's mostly soldered? (Bad Stone)

[kvandekrol]

So back when I first ventured into the DIY world almost two years ago, I used flux from Home Depot on every board I soldered. It took me... we'll just say many months to figure out why none of my builds worked reliably - they all had unstable voltages and bizarre issues beyond the hope of debugging. After thoroughly analyzing every step of my process, I finally realized that the flux itself was the problem. It wasn't electronic-grade, not rosin-based, and as a result it was causing signal bleed-through on all my builds. The first board I built without using any flux at all worked perfectly, so I threw it all away and never looked back. I've had a very high success rate since then.

Anyway, most of the boards were self-etched and therefore replaceable. (Time-consuming, yes, but it was well-deserved penance for being an idiot.) However, I do have a half-built Bad Stone board from my earlier days that has all the caps and resistors soldered to it already, and it's got flux on both sides (it bleeds through to the top side when it's soldered) so nearby components are still liable to mix signals even if the bottom side of the board is squeaky-clean.

I don't want to just plow ahead and risk it, because I had a small double-sided Madbean board that was also contaminated, and I spent about an hour scrubbing every nook and cranny on both sides with a cotton swab & rubbing alcohol and resoldering every joint and it still had unstable voltages.

I guess what I'm asking is if there's any solvent or technique I can use to get rid of all this flux reliably, especially the stuff that's underneath components that I can't get to with a swab or toothbrush. The only components on the board right now are resistors and box caps, so they'll be much more liquid-resistant than say electrolytic caps, trimmers or fragile ICs.

I'd gladly buy another board just to save the hassle, but they're all gone, I think. As I see it right now, desoldering all the components isn't an option - there are so many of them and I stand a high chance of pulling up some traces, plus it's a 4-layer board so I may mess up something internally that's unrepairable.

Anyway, any tips or ideas are appreciated!

[Mustachio]

This is what I use besides 91% iso alcohol. Fabulous blaster CC

http://www.blastergroup.com.au/contact-cleaner.html

As far as I know this stuff is pretty safe on components. It really cleans stuff good I have a few cans of it and have used it on amps and pedals with out any problems. Its strong stuff though, so you know, vented area and gloves/glasses.

[Mark Hammer]

I use methyl hydrate for cleaning flux.  Works great, and doesn't stink.

Use it safely.  Here's the MSDS sheet: http://www.wesclean.com/catelog/MSDS/200545.pdf

[davent]

For most cleanup i just use a dental pick. Cooled flux will just pop off when prodded. Easy to use on lugs, eyelets and oddly shaped joints. Then at most you'll want to use a small stiff brush to remove the loosened flux.

dave

[kvandekrol]

Cooled flux will just pop off when prodded.

Not this stuff... this is the grease If it hardened like rosin then I wouldn't have much trouble with it at all!

[John Lyons]

Denatured alcohol or Iso alcohol will work well with a toothbrush.
BUT if you have already used acid flux you have compromised your circuit board/parts/pots etc.
I'm not sure that it will keep from corroding.   That stuff seems to affect things other than the
immediate ares on the board (anything metal in the box).

[twangcat]

You cold use foam cleaner by Electrolube - SWA Safewash2000 , running water next and SRI Saferinse to remove trace ionic contamination . These cleaners are diffrent from for ex. Kontakt PCC [which is great for rosin based flux cleaning] and can remove laquer-and-grease dirt from heavy oiled transformer [verified!] . Some people would use benzine , but - if used flux has metallic component in it , or is acid based , [or both] , you must remove flux AND any conductive contaminent residue . Besides that benzine can chemically react with the board/board parts - the same is with acetone . By the way check your board mechanical connections - they can be already heavy corroded and extremely weak . The best you can do is to desolder everything , clean the board AND parts , check board for not wanted conductivity - if OK resolder parts , or even solder new  - [especially pots] , when not to expensive . Never use corrosive flux , but if you must [big steel/brass parts or so] clean them immidiately after soldering . I saw flux-corroded connections in tube amp - you could disassemble board without any soldering - just take the parts out with your bare fingers . Seriously .

[R.G.]

OK, I'll get the heresy out and over with.

Wash it. With water and dish soap, and a toothbrush.   

This could be a disaster if you don't then get the water off, but wash, brush, and when it's clean, rinse carefully with clean water (a gallon of distilled water is only $1) , shake off the droplets, then flood it or dip it with isopropyl alcohol.

Water and alcohol are miscible (i.e. mix readily) in all proportions. So with only droplets of water on the board after drain and shake, the alcohol flood mixes with the remaining water and makes a solution that's probably 99% alcohol. Drain off this mostly-alcohol solution and then shake off the excess, then let the remaining alcohol evaporate. You have removed probably 99% of the water with the draining alcohol, and the remaining 99% alcohol solution will dry FAST.

In the later 60s, IBM once used  a residential dishwasher for board cleaning at one of the sites. Wash, detergent, rinse, then hot dry was a good way to do the cleaning. I talked to a guy who ran this setup. Amazed me, but he swears it worked.

The important part is getting it dry as soon as possible after you get it clean. Water is one of the least damaging substances to almost anything if you get it dry promptly after it's clean. Water is one of the most damaging substances if you leave it there to promote corrosion.

[twangcat]

Why heresy ? . Dishwashing detergent is very good in cleaning and does almost miracles in degreasing . And it's cheap . That mixed water-alcohol fomula is used as wood cleaner before pro finishing as not to soak wood with too much water . Such a method can be very fine if you really brush out the flux . Use compressed air to remove water from the holes then a hair dryer and it's done .

[Mark Hammer]

Been a while siince someone posted a query about water-damaged pedals, but the time is right toapply what has come up before.  If you have concerns about residual water, put the cleaned board in a resealable plastic bag with some uncooked rice.  The rice will absorb the residual water over the course of aday or so.

[PRR]

> I used flux from Home Depot on every board

Back when I wuz learning to solder, simple _posession_ of plumber's ACID flux around computer/electronics assembly was INSTANT firing.

First: an iron won't get hot enough to activate acid-flux (it needs a torch). So it won't cut tarnish.

Second, if you do get a good joint today, the residual acid EATS the copper. (Not so much in plumbing, because of the torch, because the inside soon gets washed-out, and because there's more metal in a pipe than in hookup wire.)

Imagine a computer or radar, thousands or millions of joints, all critical (or they wouldn't be there). A hundred workers soldering. One guy has plumber's flux. At fire-up, there's a few problems, find and fix them. At final inspection, more problems to find and fix. Customer Acceptance, still more problems you must find and fix. Ship it out to Teterboro or up to the arctic circle, there's more problems every week and now it's more-urgent and much-more-expensive to get a geek out there to find-and-fix.

So plumber's flux was VERY bad. (When real plumbing had to be done in the same plant, the plumber's toolbox was inventoried going in and out to be sure no flux was left behind to somehow get into the electronics.)

Not so much acid-flux, but solder-joints in general were problematic. The Integrated Circuit was promoted, not so much on size or complexity, but because it could eliminate many solder joints.

You can't feel too bad about it. Obviously it has happened before, and by trained industrial solderers who "should have known better".

If all you have is leakage, you may be lucky, or maybe there's more trouble coming.

It won't even come off with the stuffs we use to remove rosin.

Dishwasher or washtub with HOT water and good scrubbing. As you know, that stuff don't come off easy. It may never come out of the corners, cracks, and vias. You might end up putting a chain on it and wearing it as hi-tek jewelry.