IPA will do. Just remember if you scrub you’ll make a paste. I apply brake cleaner liberally (see above) then wipe off changing to a fresh part of the cloth for the next wipe. Also I’ve experimented with putting a glass of brake cleaner in my ultrasonic cleaner with the PCB inside which is then rinsed off in a distilled water bath and left to dry.
I find that wiping with a cloth (or with anything really) does not work, as the fibers of the cloth are grabbed by the solder joints. You either get the cloth ripped or get small threads of cloth against the solder joints. I can only use a toothbrush reliably but then I get that “paste” and the board looks like a mess.
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Put a tissue or cloth over your toothbrush and do a single pass before moving to a different patch of the cloth.
If you submerge the board in a tray of IPA and scrub then rinse you might get better results.
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Just to make sure. Submerge, scrub, then rinse with alcohol?
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Rinse with water, preferably demineralised or distilled water (tap water contains a lot of minerals that may even conduct current, even so slightly…)
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RIght, thanks! I was thinking that tap water is not a good idea and wanted to confirm. Distilled water should do the trick.
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My current method is to scrub with 99% ipa and a toothbrush. Then blow dry with one of these bad boys. Amazon.com: Compressed Air Duster,Mini Air Duster Metal Design Enhanced Powerful 250000RPM,Infinite Speed Adjustment Wind - Portable Air Duster,No Canned Air Duster,Electric Air Blower for Cleaning Keyboard&PC : Electronics
as long as you blast it before the IPA can evaporate, it’ll take the flux with it. It’s so effective that you have to be careful where you blast the residue because that surface will then become sticky with flux.
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How much trouble have you actually had due to excess flux? I’ve been a lot more lax (and even forgotten completely to do it in some cases) and haven’t seen any problems of performance that seem attributable to that. Not questioning whether it’s a good idea, just wondering how diligent I actually need to be.
I haven’t had any problems, but I would not expect anything major in the short term. In the long term, there could be issues I guess. Personally, I began cleaning boards after noticing some serious piling up of flux in between the stripes of the stripboard. So much that I was certain that the adjacent stripes would cause short circuits if the flux absorbed some moisture.
I did not experience as much accumulation in PCBs, just some blobs like a splatter here and there. While alcohol worked nice on stripboards, it seems that flux got smeared all over the PCBs when I tried to clean it off with alcohol (rather than scrape the blobs off).
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None here either. It just … looks nicer. This Kester 63/37 solder I bought last time leaves WAY more flux residue than whatever it was I used previously. So much so that I decided to do my best to stop leaving little burnt brown snot-looking drips all over my boards whenever it was convenient enough to remove them. Also, using the mega air-blaster-5000 to purge the redidue is just fun.
In the long term, flux will corrode the copper layer.
How long that is, I have no idea…
No (visible) problem on PCBs that have been soldered and not cleaned 4 years ago.
I’ve used all sorts of methods to clean flux off boards over the years (including some of the commercial cleaners, like Servisol Electronic Circuit Board Cleaner, most of which are detailed above by others. What I tend to do now is: Where possible chip off any larger pieces mechanically (eg: point of a scribe to shatter it once it’s hardened), then use IPA with a small stiff brush (ie: toothbrush) to get the rest. Removing the large pieces first means the IPA doesn’t get diluted down too much and avoids getting extra flux residue all over the place during cleaning.
If I’m dealing with an old item where I need to touch up most/all the solder joints and it’s quite large (ie: someone else’s old kit project where they first learned to solder, where you can see looking at the board how their soldering improved while making it), then I will usually look to using one of the commercial cleaners, plugging up any holes in the board first to avoid it getting everywhere.
One thing I will note: If a board has old flux on it and you repair it, make sure you at least clean the repaired area if you touch any pads that are close together (eg: ICs, connectors, headers, transistors, etc), where the flux might touch other pads/tracks. I do this on all boards now, but I’ve noticed it more if the item is pre-2010. I’ve found sometimes that mixing different types of flux from over the years, even if neither one is a water-soluble flux, can create all sorts of issues, and some of the resulting combinations are conductive and/or more corrosive than would otherwise be expected.
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Cleaning boards also makes it much easier to check the solder joints.
Beware getting cleaners inside potentiometers, it can wash out the lubricants.
I also clean boards with IPA BEFORE doing any soldering, as sometimes they come supplied with unwelcome residue.
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This ^
I usually try to save all the mechanicals for the end so I can clean before they go on … and usually in my excitement to mount the pots and panel I also forget to follow my own advice so things never get as clean as I’d like.
Yes. Pots and switches usually go on last.
I clean the board first, check the soldering & rework, then add the final pots & switches, and gingerly clean the non-pot side with a toothbrush, doing my best not to touch the mechanicals side, then rinse gently with warm deionised water (warmer dries quicker).
If you use a toothbrush to clean the boards, don’t use the same one you clean your teeth with !
I use my wife’s instead. 
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That’s fair, I’m sure she uses yours to clean the car battery terminals.
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In many many years of soldering electronics and not removing the resin leftovers it has never caused me any problems. I’ve als not ever found a problem in a broken device that could be attributed to damage by resin.
Using low temperature leaded tin or adding some to make desoldering components a bit easier I can understand. But I’m puzzled to see people use flux when desoldering components. What is that supposed to do? Clean the surface for the replacement components? I often see people in videos prior to adding the components add even more flux?
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In my experience, there are some cases where it does make sense to use a bit of flux. Apart from helping to remove oxidation from the joint and helping with pushing and keeping oxygen out from between components and pads as the solder flows into the joint, flux lowers the surface tension of the solder as it melts, which helps it flow better. That lower surface tension isn’t just useful when you’re trying to make a new joint; it can be useful when removing solder from an existing one.
I’ll occasionally add a tiny bit of flux directly to desoldering braid on problem joints, as it can really help the solder flow off the joint and into the braid. But by tiny, I’m talking less than a pinhead amount if it’s a paste or way less than a drop if it’s liquid, and we’re usually talking large joints, say boards with heavy ground planes, +4mm dia pads, tight fitting component pins where the hole isn’t really quite big enough, etc. Flux like that really goes a long way, so you definitely do not need much.
For anything using a desoldering vacuum pump/tool however, it’s usually just way easier to add a tiny bit of solder to the joint, as that will usually provide more than enough extra flux in an easily controllable way.
Soldering SMD components usually involves solder paste, and that almost exclusively doesn’t have any flux in it, so there it’s pretty much essential. Also if you’re trying to reflow an existing SMD component (eg: a BGA chip), that lower surface tension can make all the difference.
Pretty sure however that a lot of those videos just go overboard with it, mainly I suspect cos they don’t know any better. That said, with flux the joints will in general look much shinier when the solder has melted (as it starts to flow). I can see how making it more obvious to the viewer that the solder has melted could be a useful plus for showing a process in a video. Even then, IMO they still use way too much.
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I think people often copy each others methods without investigating whether they work or are usefull.
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When I’m preparing a multi core cable end for solder my automatic habit is to dip the raw end into my plumbers flux pot then tin with an iron pre loaded with solder. I don’t bother to clean up after.
A mechanic pal still uses a huge solder gun dipped in flux for everything; it’s what his dad taught him.
Leftover flux is sticky and looks terrible; so the best thing to do is NEVER SHOW ANYONE!
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