Cleaning flux residue

[electronics man]

I have been using a "no clean" flux paste for some surface mount work recently and it leaves a horrible sticky residue. I have tried removing it by placing the board in isopropyl alcohol and washing with a stiff conductive brush for several mins. after leaving the board to dry for several mins i am still left with a sticky residue. I read online that increasing the polarity of the solvent by adding some water to the IPA works well so I placed the board in a water/IPA solution and scrubbed again then removed the water with neat IPA. but after this I am still left with the same sticky residue. It will just not come off  . any ideas for removing this residue?

[ogden]

Why don't you simply look for another flux that does not leave a horribly sticky residue?

[electronics man]

flux paste is not cheap. as far as i know most flux pastes leave residue

[ogden]

flux paste is not cheap.

They do not cost fortune as well - around $13 for 10cc syringe.

i know most flux pastes leave residue

Indeed they do not disappear completely. No clean flux pastes clean well using either pure IPA or specialized PCB cleaners. If you have problems - then problem is your paste.

[electronics man]

does anyone have experience with ones that clean well? how do i know before i buy it that it will clean well? i don't want to buy one and just have the same problem.

[ogden]

does anyone have experience with ones that clean well? how do i know before i buy it that it will clean well? i don't want to buy one and just have the same problem.

One option - see for yourself, watch some videos where flux is used in repairs. Youtuber Louis Rossmann uses Amtech Solder Flux NC-559-V2-TF, Jesse from iPad Rehab channel uses ChipQuik SMD-291 No Clean Flux. Both have no problems whatsoever using mentioned products every day.

[electronics man]

Louis uses a sonicator to clean his flux residue, if this is a necessity for cleaning then that is out of the question. the chip quick might be an option.

[ogden]

Louis uses a sonicator to clean his flux residue, if this is a necessity for cleaning then that is out of the question. the chip quick might be an option.

I'm afraid that they both routinely clean PCB's in ultrasonic bath. You better clean PCB's of portable electronics, especially high density with with BGA chips.

[nanofrog]

does anyone have experience with ones that clean well? how do i know before i buy it that it will clean well? i don't want to buy one and just have the same problem.

In the case of no-clean formulations, it comes down to the resin used. Modified rosin is much easier to clean vs. the synthetic resin based versions, which are a total bitch to clean IME. So check the datasheets carefully. In the latter case, an ultrasonic unit and appropriate cleaning solution really is called for IMHO.

As you're in the UK, Multicore/Loctite 425-01 is a version that uses modified rosin and is readily available to you. 

[electronics man]

does anyone have experience with ones that clean well? how do i know before i buy it that it will clean well? i don't want to buy one and just have the same problem.

In the case of no-clean formulations, it comes down to the resin used. Modified rosin is much easier to clean vs. the synthetic resin based versions, which are a total bitch to clean IME. So check the datasheets carefully. In the latter case, an ultrasonic unit and appropriate cleaning solution really is called for IMHO.

As you're in the UK, Multicore/Loctite 425-01 is a version that uses modified rosin and is readily available to you. 

thanks for the input, that one is £26.90 for 10 ml, which is a bit expensive but i will look for cheaper modified rosin fluxes

[Ian.M]

The problem is: even if you use a readily soluble flux and proprietary flux remover, it doesn't take much flux dissolved in the solvent to leave the board sticky.   After soaking in solvent (Flux remover, IPA or dry denatured alcohol) and brushing under solvent, you need to blot off as much solvent as possible with a lint free wipe (or at a pinch a paper towel) and a second, clean brush to press it against the board, so that as much as possible of the residual dissolved flux is transferred from the board to the wipe, then immediately rinse with clean solvent (easiest to spray it and brush with the brush from the previous step, letting the runoff drain into your initial wash bath).   If  you need minimal ionic residues, you may need to then wash (scrub) with hot water + a trace of unscented dish detergent, rinse thoroughly, shake off excess water, rinse with distilled or deionised water, shake again, rinse with dry IPA to form an azeotrope with any trapped water under components, shake again then dry with 90°C hot air, in a very well ventilated location.

[Gary.M]

It's no clean, why clean it?

[electronics man]

It's no clean, why clean it?

because the board gets covered in horrible sticky crap that attracts dust and is absolutely disgusting. this isn't just a bit of white residue.

[nanofrog]

It's no clean, why clean it?

It's not the same thing as the flux core of solder wire, where there's only a small amount left on the board that's hardened. Using additional flux can make sure you don't get bridges (i.e drag soldering an IC), but it's unsightly to leave it IMHO (one hell of a mess left behind if you don't, as it's not hardened).

[KL27x]

because the board gets covered in horrible sticky crap that attracts dust and is absolutely disgusting. this isn't just a bit of white residue.

Most no clean and rosin fluxes will be sticky at first but will eventually dry out. Paste fluxes are made to dry out slower, for longer rework times. That said, there are some weird no cleans out there.

Disgusting is subjective, but once dried out most flux residue should not hold dust or feel tacky at room temp. For most liquid flux, it is a typically a matter of a few minutes after soldering before the flux dries out, but it depends on how much you slather on there and how much heat you give it. It might take hours. Paste flux might take a little longer to dry out. Once dry, the residue is typically hard at room temp and will shatter if pressed with say the tip of a knife.

The kind of no cleans that leave a bit of white residue, that sounds like a low solids no clean. That is typically a bit more conductive than a bulky "gross" rosin/resin residue. One of the main advantages is it looks better. The white stuff is ionic residue which is conductive when wet with normal humidity. It is present in all flux residue, but in most electrical flux, the "gross," initially sticky rosin/resin encapsulates it (and renders it inert), so you don't actually see it. You might also see white residue left over after incomplete cleaning of flux residue. Alcohol will dissolve the resin, but unless you mechanically clean/brush/US you can inadvertently leave some of the naked white stuff on the board.

[Gary.M]

The OP might look for a water clean flux... Washes off easily in warm water in my experience.

[nanofrog]

The OP might look for a water clean flux... Washes off easily in warm water in my experience.

Easier to clean, but must be cleaned off so it doesn't corrode the joints.

[Ian.M]

Yep.  It only takes *ONE* spot of water washable flux trapped under a chip to eat through a track or lead within a few months.  That's an acceptable risk for mass production with automated board washing + excellent process control as the small increase in in-warranty failures is offset by the vastly reduced environmental regulations compliance cost and lower fire insurance cost gained by avoiding V.O.C.s.

IMHO water washable fluxes are totally unsuitable for any sort of manual rework, repair or prototyping unless you've got an automatic board washer (think: glorified all stainless dishwasher) as good as a typical production line one, and are careful to minimise flux usage.   Ultrasonic cleaner wash and rinse tanks are a poor substitute due to the risk of component damage from the prolonged exposure to high level ultrasound required to be certain *ALL* the flux has washed away from *ALL* crevices.

[KL27x]

Funny though that the product description ways to wash to flux with alcohol. But the datasheet says water.

It's a travesty they even call this "rosin" paste flux.

If you use any mil spec liquid rosin flux, it is not water soluble and it probably meets w/e requirements that manufacturers make up to qualify as "no clean."

So we have a bunch of people insisting that electrical flux must be labeled "no clean," which is exactly what manufacturers want us to think. AFAIC, the surest way to get good electrical flux is to start with mil spec rosin. Most no cleans will be fine. But every mil spec rosin flux will be fine for electrical work. A mil spec rosin flux will be designated R/RA/RMA. This "rosin paste flux" is an atrocity, by all appearances.

[ogden]

AFAIC, the surest way to get good electrical flux is to start with mil spec rosin.

I heard that so simple tools as "mil spec" hammers (not to mention mil spec WC equipment) are way too expensive for general public. What about flux?

[nanofrog]

AFAIC, the surest way to get good electrical flux is to start with mil spec rosin.

I heard that so simple tools as "mil spec" hammers (not to mention mil spec WC equipment) are way too expensive for general public. What about flux?

Not expensive.

Look at Kester's rosin based flux products for example.

[KL27x]

I use MG 835 RA flux. It's $25.00 for a liter. I share with another business. I have probably used half a liter in my lifetime, thus far.

I started out with 125mL bottles. I have previously used Alpha Metals, and that is also mil spec. Same stuff. The name on the bottle doesn't really matter if it meets mil spec. This right here is the biggest reason manufacturers don't like selling it. Their name doesn't add value. It's more of a known commodity rather than a name brand product. If they upcharge, the consumer will buy it from someone else. So most manufacturers of fluxes don't sell it in smaller quantities than 1 gallon. But they will sell you their own schmoo for $20.00 a syringe.

[Gary.M]

Perhaps for small jobs without any cleaning after use...

https://www.kester.com/products/product/tsf-6522rh


??

[nanofrog]

For those in the US/CAN, CML Supply (they also sell through eBay) repackages Kester's 1544, 186, 951, and 959T liquid fluxes in hobbyist/repair shop friendly sizes ($5.13 for 2oz. needle dispensing bottles). 

[Bud]

The last Kester i bought from CML Supplies came unusable, too thick and dry. Do not know if they perform any quality inspection when repackaging. Will not buy from them anymore.

[MudAndSnow]

Isoprop alch will loosen the flux but that doesn't remove it from the board.

I do this:
1 - scrub with brush and isoprop
2 - wipe off brush and pcb with kimwipe
3 - lay new kimwipe on pcb and then use brush to push kimwipe into tight spots

Kimtech wipes:
https://www.digikey.com/product-detail/en/mg-chemicals/830-34155/473-1118-ND/1278230

Brushes (I cut the bristles to make it stiffer):
https://www.digikey.com/product-detail/en/mg-chemicals/855-5/473-1048-ND/949490

[nanofrog]

The last Kester i bought from CML Supplies came unusable, too thick and dry. Do not know if they perform any quality inspection when repackaging. Will not buy from them anymore.

I've never run into this from them thus far, so good to know (have made my few orders during the winter).

FWIW I buy Kester's RF741 flux from typical distributors, but it's not been repackaged. There are even sellers on eBay that repackage some of Kester's liquid flux products (I bought some 186 to see if it was genuine before knowing anything about CML Supply; turns out it was).

[aandrew]

I typically use isoprop alone to clean boards, but have noticed that it doesn't actually *remove* flux, just dissolve it and spread it around everywhere. I'm going to give that 1:1 acetone:isoprop a try, although I can't seem to find reasonable quantities of not-super-smelly nail polish remover. I can buy pure acetone by the gallon but that's far far far too much for what I use.

[nanofrog]

I typically use isoprop alone to clean boards, but have noticed that it doesn't actually *remove* flux, just dissolve it and spread it around everywhere. I'm going to give that 1:1 acetone:isoprop a try, although I can't seem to find reasonable quantities of not-super-smelly nail polish remover. I can buy pure acetone by the gallon but that's far far far too much for what I use.

Check the paint department of Home Depot or similar. I get it in quart sizes, but they offer it in a pint sized can too (Klean Strip brand).

[KL27x]

The last Kester i bought from CML Supplies came unusable, too thick and dry. Do not know if they perform any quality inspection when repackaging. Will not buy from them anymore.

I haven't used Kester, but the solvent used in MG 835 RA is very difficult to contain. Even in the original bottle, the solvent slowly escapes through the plastic. In smaller quantities the packaging would be even more important.

I store my main supply in a glass bottle with a thick O-ringed HDPE stopper I fabbed up after the original plastic cap to the bottle started to crack and break into pieces. That works fine, as long as you don't let the O-ring get direct contact with the flux.

[nanofrog]

I haven't used Kester, but the solvent used in MG 835 RA is very difficult to contain. Even in the original bottle, the solvent slowly escapes through the plastic. In smaller quantities the packaging would be even more important.

I store my main supply in a glass bottle with a thick O-ringed HDPE stopper I fabbed up after the original plastic cap to the bottle started to crack and break into pieces. That works fine, as long as you don't let the O-ring get direct contact with the flux.

FWIW, I store mine in amber round glass Boston bottles for that reason.

[aandrew]

Check the paint department of Home Depot or similar. I get it in quart sizes, but they offer it in a pint sized can too

I don't know why I didn't think of paint stores. I can get 1L of acetone for $10 there. Thank you!

[mmagin]

I really like using a water soluble flux to assemble everything that is washable.  I don't use an ultrasonic cleaner yet, but a good soak in 60C water with detergent, followed by a lot of hot water rinsing, final rinse in distilled/di water with a some isopropanol as a wetting agent, then forced air drying.

I'll go back and solder the non-washable parts with a no-clean or conventional rosin flux.

I don't especially like the idea of using a non-water-soluble flux and then just solvent cleaning by hand, I think it just smears it all over, probably negating the value of that step.  (Sure, a whole tank of solvent or better yet, vapor phase cleaning would be good.)  Some day I should make a test board and do some electrometer measurements to put some science to my opinions.

[ANTALIFE]

Why not just get a more liquidy flux like this:
https://au.element14.com/multicore-loctite/mfr-301/flux-mfr-301-5l/dp/1115469

and then dilute it with a thinner like IPA?

[usagi]

i use whatever flux i like without limitation or worry.

i'm lazy, harbor freight ultrasonic cleaner with branson EC gets them spotless. and takes zero effort. doesn't matter what flux it is.

[nanofrog]

i use whatever flux i like without limitation or worry.

i'm lazy, harbor freight ultrasonic cleaner with branson EC gets them spotless. and takes zero effort. doesn't matter what flux it is.

Branson EC is definitely good stuff. And if you clean a lot of boards, that's definitely the way to go.

But I don't think most of us are cleaning boards all that often; maybe 1 or 2 per week max in my case, so harder to justify (and make room for).

[usagi]

i don't clean a lot of boards. i'm just lazy so the ultrasonic does all the work for me and i don't have to lift a finger. gets the boards spotless with zero effort.

if you have the room for a loaf of bread you have the room for the ultrasonic.

[nanofrog]

i don't clean a lot of boards. i'm just lazy so the ultrasonic does all the work for me and i don't have to lift a finger. gets the boards spotless with zero effort.

if you have the room for a loaf of bread you have the room for the ultrasonic.

True, I wouldn't need a big one (think a 2.5L would be plenty). I'd love to have an Elma, but that's well out of my budget (S30H).

I'd want one with degas and sweep functions as well as heated, and the X-Tronic 3L Platinum Edition ticks the boxes for $230. Tempting, so I'll have to mull this one over as I'm on the lazy side myself.  Toss in a gallon of Branson EC, and it's still under $300. 

[usagi]

for cleaning PCBs, just heated with branson EC is all that is needed. you can manually degas.

sweep is only needed for large items in large cleaners which require heavy duty cleaning. not something needed for your average hobbyist PCBs.

HF Ultrasonic Cleaner + 20% coupon + basket
branson EC

and there you go.

[mrpackethead]

I use Henkel GC10 paste and do most of my reflow using Vapour Phase. The really nice thing about that is that the flux ends up in the bottom of the tank and not on the board.    The nasty thing about that is the periodic job of cleaning the tank, which beomces very brown and sticky after several hundred cycles.  However the result is amazingly clean boards.

[nanofrog]

branson EC

Forget Amazon. All-Spec sells the 1 gallon size of Branson EC for $33.97 (here).   

[electronics man]

I typically use isoprop alone to clean boards, but have noticed that it doesn't actually *remove* flux, just dissolve it and spread it around everywhere. I'm going to give that 1:1 acetone:isoprop a try, although I can't seem to find reasonable quantities of not-super-smelly nail polish remover. I can buy pure acetone by the gallon but that's far far far too much for what I use.

I wouldn't use acetone as it very harsh to plastics and could damage components

[electronics man]

i have found that soaking a lint free cloth in IPA and wiping the board does a good job of cleaning, also i have started using less flux in the first place.

[usagi]

I'm going to give that 1:1 acetone:isoprop a try

not a good idea. acetone destroys many plastics. ABS, polyethylene, acrylic, polycarbonate, pvc, etc.

[nanofrog]

I'm going to give that 1:1 acetone:isoprop a try

not a good idea. acetone destroys many plastics. ABS, polyethylene, acrylic, polycarbonate, pvc, etc.

Agreed.

I'd actually recommend giving an 80/20 mix of IPA or (50/50*) Denatured Alcohol with Xylene a try for more stubborn deposits. Past that, would be MEK if you can get it (MEK = Methyl Ethyl Ketone), and finally, acetone on stuff you know it's not going to solve (i.e. you'll need to test it first, but generally speaking, connectors don't tolerate it well at all).

* Klean Strip brand (not the green crap) that's a ~50/50 mix of ethanol & methanol. Regardless of the mix or brand, it needs to leave zero residue on the surface of the glass it evaporates from in order to be usable.

[eb4fbz]

If you want to clean your boards to have them free of flux residue, dont use no-clean flux solder paste, that thing is a PITA to remove. Use a water based flux instead.

[nanofrog]

If you want to clean your boards to have them free of flux residue, dont use no-clean flux solder paste, that thing is a PITA to remove. Use a water based flux instead.

Depends on what it uses for resin. Some are based on modified rosin, which can be cleaned without Herculean effort (not much different than typical rosin based fluxes, with low solids versions being the easiest to clean, even for rosin based fluxes).

It's the synthetic resin based versions of no-clean that are a serious PITA to get off your PCB's with typical hand cleaning techniques. So check the datasheets to see which type it uses, and choose accordingly. 

That said, there are standard rosin based fluxes available, and it seems TME carries such products from well known manufacturers at reasonable prices in syringes, jars, and metal tins (here). 

[chickenHeadKnob]

MG Chemicals Heavy duty Flux remover contains Ethyl Acetate, Acetone, 1,1-Difluoroethane and isopropyl. It works with reasonable aggression on rosin flux and hasn't damaged any of my boards (yet) but I am just a hobby low-time user. I don't let it soak in too long, maybe a minute, scrub with brush  and then follow up with a isopropanol rinse.

 I have heard of 20/80 % ratio of Ethyl Acetate/isopropanol as a home mix substitute.  I am not an economic nationalist however because MG Chem is Canadian my local electronics shop 60Km away has it in stock and I like to patronize them so they stay in business. Enlightened self interest you could say.

[SeanB]

I have a potted module that has been soaking in MEK for a month now, trying to soften the potting compound so I can see what this electrometer amplifier looks like ( my bets are a JFET and some resistors), and still no joy. Might have to get a little more aggressive on the solvent, but still want to have the plastic survive.

Flux residue start first with a new toothbrush, some alcohol and scrub it, then only if that fails move up to spot cleaning with more aggressive solvents in the spots only.  Generally IPA is fine for 99% of the cleaning, as you cannot get Freons any more, which were a superior cleaner.

[nanofrog]

Flux residue start first with a new toothbrush, some alcohol and scrub it, then only if that fails move up to spot cleaning with more aggressive solvents in the spots only.  Generally IPA is fine for 99% of the cleaning, as you cannot get Freons any more, which were a superior cleaner.

Indeed.  Saw that stuff in action decades ago at Martin Marietta, later becoming Lockheed Martin whilst I was there, and it was amazing. Former boss of mine told me about using at Fluke back in the early '80's as well.

Benzine is highly restricted these days IME, but getting your hands on some Toluene may actually be feasible (local paint store might have it). FWIW, it's available to me and I keep a quart on-hand. Rarely used, but still nice to have if needed.

As per removing the potting compound you mentioned, you may want to start with mechanical removal using a rotary tool of some sort (Proxxon, Dremel, air powered die grinder, ...).  Should speed up the process greatly once you find the right solvent. 

[Bassman59]

i use whatever flux i like without limitation or worry.

i'm lazy, harbor freight ultrasonic cleaner with branson EC gets them spotless. and takes zero effort. doesn't matter what flux it is.

Is this the cleaner you have?

[usagi]

i use whatever flux i like without limitation or worry.

i'm lazy, harbor freight ultrasonic cleaner with branson EC gets them spotless. and takes zero effort. doesn't matter what flux it is.

Is this the cleaner you have?

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