Flux, "No Clean" Flux, Cleaning, and Re-Coating? - Page 1
Forum section: electronics / repair

author: Fried Chicken
author_rank: Regular Contributor
timestamp: January 09, 2025, 07:24:10 am
content: I'm getting deeper into soldering work, and I'm having trouble understanding, using, applying, cleaning, flux, etc.It sounds obvious but it's not. I have some Chip-Quik "no clean" flux I got from mouser that comes in a syringe. It takes quite a bit of effort to get out of the tube, and doesn't apply well in small amounts. As a result I end up with flux everywhere I don't want it, and then cleaning becomes a mess.I have a chip-quik marker applicator that applies very little flux, which I like, only onto the parts I need fluxed, but the marker tip got all destroyed, and it's quite fat so hard to reach onto some solder points.But then it comes to cleaning, right now I'm using 91% IPA b/c it's cheap and plentiful. I have a special flux remover spray that claims all sorts of good things, but while it might be healthy for the board, I'm not sure it's healthy for the user.I noticed now too, after having done some work on a pretty mission critical board that the board looks very "dry", like the coating might have been removed. Should I recoat these boards? Lacquer? Polyurethane?Does someone have a recommendation for a flux that's easy to deal with? Do I not have to clean "no clean" fluxes?I've done research in this area, but specific recommendations and advice would be highly appreciated!

author: Smokey
author_rank: Super Contributor
timestamp: January 09, 2025, 08:22:12 am
content: https://www.eevblog.com/forum/chat/good-soldering-flux/msg5237004/#msg5237004https://www.digikey.com/en/products/detail/sra-soldering-products/TF5000/10709784IPA and a tooth brush for the first scrubbing. Then another IPA rinse until clean.(no-clean just means that if properly used it won't eat holes in the board after use)

author: NE666
author_rank: Frequent Contributor
timestamp: January 09, 2025, 09:49:54 am
content: Quote from: Fried Chicken on January 09, 2025, 07:24:10 amNot wanting to hijack the OP's thread but I'm having a very similar experience. I just recently started trying to use gel/paste flux, as opposed to pens and liquids, and purchased MG Chemical's 8341 "No Clean Flux Paste".I had expectations, based on what I've seen used in various YT reworking videos, of something akin to toothpaste viscosity and slump, whereas what I have is much more like a stiff Vaseline jelly. On dispensing, it seems to prefer adhering to itself and the syringe tip rather than the PCB. It's wasteful and annoying to work with.Can anyone recommend something easier to work with, in terms of fluidity, adhesion and ease of dispensing manually from a syringe?

author: coromonadalix
author_rank: Super Contributor
timestamp: January 09, 2025, 04:46:09 pm
content: for the syringe paste you have many with different use and densities, i use the ones for smd, softer smoother easier to apply and dont runfrom QuickChip, i dont have the part on hand but smd use everywhere lolland the no "flux clean", tried them but it leave a sticky hard residue, very hard to remove if you really need a clean borad from Aim brand (dont know the others),and we did saw some problems in hf uhf equipment, reverted to the ol 63/37 60/40 ROHS ones are a pain in the @, you need to flux many times and the flux sip everywherewe use aqueous cleaners lie Atron and Vigon

author: tooki
author_rank: Super Contributor
timestamp: January 09, 2025, 06:11:32 pm
content: Quote from: Fried Chicken on January 09, 2025, 07:24:10 amWhat kind of nozzle are you using? For thick products like flux gel, I recommend using a conical tip. This requires far less force than a straight tip like a needle. A very fine conical tip will give you good control without undue force.Which flux did you get? ChipQuik makes many no-clean fluxes, some of which are much lower viscosity than others. Please give a complete model number (in particular, don’t truncate letters: for example, SMD291 and SMD291NL are not the same product!).Quote from: Fried Chicken on January 09, 2025, 07:24:10 amYou can buy replacement pen nibs.But if you really want careful control of a liquid flux, look at the Bon-Kote series of flux pens. They come in various brush tips. They’re sold empty and you fill them with your flux of choice. Buy only from an authorized dealer (expect to pay $30 for it), as the ones found on AliExpress, etc. are invariably fakes, and those have a reputation for performing poorly.Quote from: Fried Chicken on January 09, 2025, 07:24:10 amIPA is not the best flux cleaner, no matter how many people claim that it is. <99%, even worse. IPA will get off most of it, but the problem is that “most” isn’t good enough. What gets left behind are any bits of really burnt flux (usually harmless, but ugly) and ionic contaminants, which are now no longer entombed in flux residue.Commercial flux cleaners do better, by using blends of solvents that together keep everything dissolved. But you still need proper technique.If you have access to an ultrasonic cleaner that your boards fit in, this is my favorite way to clean them. You can either use small amounts of solvent in a small container or baggie floating in a bath of water (do not fill an ultrasonic bath with flammable solvent!!!!), or you can use water-soluble no-clean flux, or you can use a water-based (aqueous) flux cleaner like Electrolube Safewash Super (SWAS), which does a perfect job.Quote from: Fried Chicken on January 09, 2025, 07:24:10 amI like ChipQuik SMD291NL.SMD191 is their “smooth flow” flux, and it really is much “looser” in consistency, but it is a more delicate flux, in that it is “spent” after being heated once. So it’s fine for assembly, but not great for rework or drag soldering, where you may go over a joint a few times before you’re done. SMD291NL is better at that, and has the unusual characteristic of being crystal clear (amber, but not opaque at all) even at room temperature, so it doesn’t totally occlude things as you apply the flux. Really handy under the microscope.No-clean residues are safe to leave on, butonly if the flux has been fully heated to soldering temperature to neutralize it.Many no-clean fluxes are corrosive if they haven’t been heated. When hand soldering with an iron or hot air, some of it will get warmed enough to get runny and flow away, but not get heated enough. The only way to guarantee it gets hot enough to neutralize is when reflowing in an oven. Upshot is, when I hand solder, I always clean the flux.

author: Fried Chicken
author_rank: Regular Contributor
timestamp: January 10, 2025, 05:18:05 pm
content: Quote from: tooki on January 09, 2025, 06:11:32 pmSorry for the late reply to your incredibly helpful and illuminating post! I had to go to my solder station and actually check what I have. It turns out I lied: I have MG Chemicals 8341 No Clean Flux Paste.As I said very thick, very difficult to squeeze out of the syringe, and very difficult to apply in minute amounts. The quality of the syringe is very nice though.QuoteI have the ChipQuik CQ4LF. It came with a replacement marker nib, but that one is also destroyed. I've now turned it around, stuffing the fuzzy end into the marker, and it's again new, and hopefully for longer since for a while it was my only flux and I had to squeeze it in every which way onto the component.I will look at the Bon Kote flux pens, it looks almost like a fountain pen but for flux! That might be perfect.QuoteI do not have an ultrasonic cleaner, an,d I won't get one unless/until I can afford/justify/acquire for cheap a proper industrial unit sufficiently large for more than just PCB work.I really like IPA as a solvent/cleaner b/c afaik it's relatively "healthy". I have a commercial cleaner spray, I don't trust it.The Electrolube Safewash looks nice, I will see if I can find it from any local retailer.QuoteI'll look at the SMD291NL, since I've found the Rossmanian technique of flooding a board with flux just creates an unnecessary mess. I guess it doesn't matter if you have a PCB dishwasher, but that still doesn't help if you're working on a boardin situ.This calls into question the use of "no-clean" flux if you really genuinely do have to clean it anyway. In lieu of that I would prefer an "easy clean" flux that gets neutralized with something like IPA or has a volatile element to it.Right now the way I clean the boards is IPA and then compressed air (either canned air, or taking it out to the garage and using it with my shop air).

author: Fried Chicken
author_rank: Regular Contributor
timestamp: January 15, 2025, 06:12:17 am
content: Quote from: tooki on January 09, 2025, 06:11:32 pmSo in lieu of a "no clean" flux, are there any "cleaning required" fluxes that clean up significantly easier/better? If I'm going to be cleaning anyway, might as well get something w/o comrpomise no?

author: forrestc
author_rank: Unknown
timestamp: January 15, 2025, 06:37:59 am
content: Let me add my overall perspective on this, with the caveat that I'm talking broadly here, and there are lots of exceptions:If you are using a no-clean flux, you shouldn't clean it UNLESS you are prepared to do a really thorough job of cleaning theentireboard. Most no-clean fluxes are designed such that a normal soldering process will encapsulate the acids in inert flux residues. If you apply any cleaner to the board, generally, that will disturb any no-clean flux residues on the board and cause them to no longer behave properly to avoid corrosion. As a result, if you clean you must clean the entire board. As one industry expert puts it: There is such a thing as selective soldering, but there isn't such a thing as selective cleaning.In addition, no clean fluxes are not necessarily designed to be cleaned with IPA. Often you will leave a worse residue on the board after attempting to clean with IPA than if you left it alone. Make sure that whatever you clean the board with is designed to dissolve the specific flux you are using.It is important to understand what has to be done to a no-clean flux for it to actually be no clean. Most of the fluxes on the market have to be heated above a certain temperature for a certain amount of time so that they are no longer active. Some don't. The phrase you need to see is "passes SIR test in a unreflowed state", or "passes SIR test once ...".In my production facility, we use TACFLUX-020 wherever we can't be sure that are able to get all of the flux activated/inerted. Although it still might be beyond what you want to pay - don't get scared away by the indium website which lists a scary list price - Tequipment has it for like $23 for a big syringe. The TACFLUX-020B is a slightly different formulation - one of the two is a bit thicker. We will typically transfer some into a smaller syringe and then use a straight needle to dispense, with the needle being sized such that it's small enough you don't get big blobs and large enough you can still push it out. BTW, we also use TACflux 089HF for those cases when we are 100% sure we'll be activating it all. It tends to be a bit more active/aggressive so it's easier to rework using it, but then you run the risk of having residues which can cause corrosion.As far as getting a water wash flux, I really would recommend avoiding those unless you are prepared to really clean using water including spraying under packages and the like. The problem is that "water clean" really means "absolutely must clean or you will have problems eventually".One big caveat to the above is that this is based on doing quantity production. When building one or two, all of the stuff about corrosion and the like probably doesn't matter unless you plan on putting it outside or in a high humidity environment.Even if you can't/don't want to afford the TACFLUX, there are others out there. Be aware that you should be looking for a rework flux which should be fairly easy to dispense.

author: Fried Chicken
author_rank: Regular Contributor
timestamp: January 16, 2025, 12:46:12 am
content: So I just bought a Hakko flux pen, and I need to order some solder/flux anyway.What would be a good flux to put into it? Something that cleans up easily with IPA would be nice.I'm kind of a fan of 63/37 solder, why isn't it more common? Or should I just get 60/40?

author: David Hess
author_rank: Super Contributor
timestamp: January 16, 2025, 01:59:04 am
content: Isopropyl alcohol has the virtue of being inexpensive, readily available, and safe, but by itself it is not a very good flux cleaner. A mixture of 50/50 isopropyl alcohol and toluene is much better, and a great flux thinner, but toluene is no longer readily available.Quote from: Fried Chicken on January 16, 2025, 12:46:12 amSn60Pb40 is slightly less expensive than Sn63Pb37. Otherwise they are practically identical.

author: Fried Chicken
author_rank: Regular Contributor
timestamp: January 16, 2025, 05:06:13 am
content: Quote from: David Hess on January 16, 2025, 01:59:04 amAre there any fluxes that clean well with IPA?I'm genuinely allergic to nasty solvents as I do my work basically in the house.

author: aeberbach
author_rank: Regular Contributor
timestamp: January 16, 2025, 08:29:49 am
content: If the flux is hard, such as produced by rosin-core solder, use a soft tool like a bamboo skewer to chip off the big lumps of flux first and then brush/vacuum the board before using the IPA. It will take about half the time to fully clean.

author: David Hess
author_rank: Super Contributor
timestamp: January 16, 2025, 04:21:27 pm
content: Quote from: Fried Chicken on January 16, 2025, 05:06:13 amThe water soluble fluxes might clean well with only IPA, but you should not be using them anyway.I never had good results using only IPA with any flux. I have tended to use acetone, which other than being flammable is one of the least toxic options. I would test and use MEK and toluene if I could get them more easily. Degreasers like 1,1,1-Trichloroethane are excellent at removing flux. Maybe spray brake or carburetor cleaner would be a good option?You could examine the MSDSes for various spray flux removers to get some ideas. They usually work very well.

author: Fried Chicken
author_rank: Regular Contributor
timestamp: January 16, 2025, 09:16:15 pm
content: Quote from: David Hess on January 16, 2025, 04:21:27 pmI. Am. Losing. My. Mind. Here.Acetone is likely the move. I'll skip the water cleanup fluxes. Now I just need to decide on which flux to purchase. I got a flux pen, so I guess I need a less viscous flux for that, and I still have my existing MG flux that seems pretty corrosive if not cleaned.Recommendations are:SMD291NLfor its low viscosity and re-usability, TACFLUX-020 ($23 from Tequipment for 10cc) or TACFLUX-020B ($28 from Tequipment for 30cc) as it "passes SIR test in a unreflowed state" or "passes SIR test once ...". I found this on tequipment, but it had a low recommended use temperature.A recommendation for exclusively SMT/SMD flux b/c it's somehow better.And for solder: Skip the ROHS compliant; but now there's a million options for solder, 60/40, 63/37, lead-free, various flux core types, and diameters.Writing all this down as notes for myself.I. Am. Losing. My. Mind. Here.