Cleaning PCB soldering paste residues  - Page 1
Forum section: electronics / beginners

author: sairfan1
author_rank: Frequent Contributor
timestamp: September 21, 2023, 09:18:32 pm
content: What is the handy way to clean PCBs after soldering.

author: Jackster
author_rank: Frequent Contributor
timestamp: September 21, 2023, 10:44:11 pm
content: Put it in the dish washer...You can get PCB cleaner in a spray bottle or aerosol. Use an ESD brush to work out the flux and wash it down with distilled water or IPA.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: September 22, 2023, 01:31:58 am
content: I use a toothbrush and flux cleaner. Don't just spray it on, rinse the board with it. Spraying on doesn't rinse the rosen away. Those toothbrushes the dentist give you are perfect. (Yes, maybe, it should be an ESD, but there's no way you need to worry about ESD if the board is wet with flux cleaner.)

author: sairfan1
author_rank: Frequent Contributor
timestamp: September 22, 2023, 02:42:01 am
content: IPA is rubbing alchohal? or its different thing, can we use it in ultrasonic as well?As you guys also talked about spray what kind of chemical it has? I was looking for genrally available cheaper solution

author: tooki
author_rank: Super Contributor
timestamp: September 22, 2023, 05:22:18 am
content: IPA (and other solvents) work well in ultrasonic cleaners. However, it’s dangerous to do unless it’s an ultrasonic cleaner specifically made to work with flammable liquids! It’s better to use a water-based cleaner like Safewash. (Or Zep floor stripper, which is chemically almost the same but costs way less.)Note that many modern fluxes do not dissolve fully in IPA, leaving behind white chalky residue. Commercial flux cleaners do better, leaving less (or no) white residue, and needing a smaller amount to do so.

author: tooki
author_rank: Super Contributor
timestamp: September 22, 2023, 05:24:01 am
content: Quote from: JustMeHere on September 22, 2023, 01:31:58 amI’ve mostly switched from rinsing away with solvent to instead mopping it clean with wipes (like kimwipes) or cotton swabs. You use up far, far less solvent that way.

author: u666sa
author_rank: Frequent Contributor
timestamp: September 22, 2023, 07:40:35 am
content: Quote from: sairfan1 on September 22, 2023, 02:42:01 amLook for benzene in your local hardware store. Same as with flux off, you agitate it with hard tooth brush. (tooth brushes are sold in different hardnesses)IPA is crap IMO. At least that IPA that I get my hands on. It is 99% alcohol, and 1% water. That 1% water leaves white residue after it dries off.Anything you use will leave some flux on board, which is okey, since it is dissolved. If you want super clean effect you need to use ultrasonic cleaner.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: September 22, 2023, 09:50:13 am
content: I use aerosol flux remover with a small brush. To get into tight spaces, I use a TePe interdental brush, it is one of the tiny brushes to clean between your teeth.https://www.tepe.com/uk/Products/interdental-brushes/tepe-interdental-brush-original-pink/SJ

author: jpanhalt
author_rank: Super Contributor
timestamp: September 22, 2023, 10:05:50 am
content: Quote from: u666sa on September 22, 2023, 07:40:35 amAuthor is in Canada. I very much doubt "benzene" is at any consumer store. Perhaps you mean a mixture of aromatic hydrocarbons (xylene + toluene) or something we might call naphtha or Stoddard solvent?As for IPA (isopropyl alcohol, 2-propanol), I find that 99% works, but it is not my preferred solvent. Rubbing alcohol is typically 60% to 70% IPA and the remainder is water.

author: jpanhalt
author_rank: Super Contributor
timestamp: September 22, 2023, 10:10:21 am
content: @tookiGlad to see you have been "Zepped."

author: Skashkash
author_rank: Regular Contributor
timestamp: September 22, 2023, 12:35:17 pm
content: The question really starts with what type of flux you are cleaning off the PCB.I've had lots of residue issues with rosin based fluxes. 99% IPA works, but really needs some mechanical assist like a good brushing to work.You can add a saponifier and a little acetone to the IPA to improve results (that may be what's in some commercial flux removers). But I still had some white residue issues.Straight acetone or even brake cleaner works, but those chemicals are way too aggressive for my tastes and risk damaging parts on the board and maybe even your health.Too bad trichloroethylene is not commonly available any more. That stuff worked great as a flux remover.These days I've shifted over to using no clean or water clean fluxes in my solder pastes and wire solders.Cleans up perfectly with just warm water when pcb cleaning is necessary.

author: liaifat85
author_rank: Regular Contributor
timestamp: September 22, 2023, 01:16:10 pm
content: Hopefully this video will help you regarding PCB solder flux cleaning methods:If you wanna know about Ultrasonic cleaning, you can see here too:https://www.pcbway.com/blog/Engineering_Technical/Safely_Tips_of_Cleaning_PCB_With_Ultrasonic_Cleaning.html

author: sinewave
author_rank: Unknown
timestamp: September 22, 2023, 01:20:50 pm
content: I use a couple different methods, my preferred method is to let it soak in 99.997% IPA for 12 hours and use a KimWipe and a toothbrush to dry it (and remove anything left behind) or for especially bad residues I use my PCB wash in an ultrasonic cleaner.

author: Vovk_Z
author_rank: Super Contributor
timestamp: September 22, 2023, 02:22:11 pm
content: There is ready-made solution - liquid PCB-cleaner. It consists of IPA plus a bit of pure benzine (universal cleaner, IDK it's English name).It cleans PCB very good and fast with toothbrush or other brush (until you need ultra-clean for ultra-precision circuits, then you need additional special cleaning).

author: PlainName
author_rank: Super Contributor
timestamp: September 22, 2023, 03:12:48 pm
content: Quote from: sairfan1 on September 21, 2023, 09:18:32 pmDifferent methods for differernt scenarios, and not sure what you're asking here - an entire PCB after it's been built from scratch or small mods to an existing build board.For the latter, and single complete builds, I use IPA and kitchen towel. Rossman and NorthridgeFix videos show the method many, many times: flood the area with IPA, soak up with towel. Done. (But note that 'flood' is relative to the size of the repair and amount of flux - often it is a few drops.) The idea is that the IPA dissolves the flux so the towel can suck it all up through capillary action. Usually doesn't need any more wiping than just mopping up the IPA. Other methods that don't dissolve the flux just smear it over a greater surface.Where there is a problem, and the simple mopping doesn't work, I use an electric toothbrush to agitate things. Used to use manual toothbrush (no lack of supply, see) but the electric one is much kinder and more accurate. Lidl/Nevadent do a battery one that's ideal (which I prefer over the rechargable) for about a tenner.

author: sairfan1
author_rank: Frequent Contributor
timestamp: September 22, 2023, 06:38:54 pm
content: I was asking for newly assembled PCBs, some PCBs could have tricky component like if I have soldered ESP32 module on PCB as they have a metal casing and such liquid can be stored inside it, I can't dip such PCBs in IPA or other chemicals.

author: jpanhalt
author_rank: Super Contributor
timestamp: September 22, 2023, 07:16:44 pm
content: Do everything that can be immersed. Clean, then hand solder (or reflow) what can't be immersed and spot clean those areas. That's what I do for button switches. Although, some are sold as liquid tight.

author: twospoons
author_rank: Frequent Contributor
timestamp: September 22, 2023, 07:24:27 pm
content: Quote from: Jackster on September 21, 2023, 10:44:11 pmTried a water-soluble flux remover one time. Foam in a can - spray on, scrub, rinse off with water. It was a very strange feeling running a PCB under the kitchen faucet!These days I like to use Fluxclene, made by Electrolube. Its a mixture primarily of hexane (white gas / white spririt), isopropyl alcohol and orange terpenes. That stuff will dissolve all sorts of resinous or oily crap - I don't just use it on PCBs.

author: jpanhalt
author_rank: Super Contributor
timestamp: September 22, 2023, 07:30:41 pm
content: Quote from: twospoons on September 22, 2023, 07:24:27 pmI must admit, the first time I used a water-based flux remover (Kester rosin flux and solder paste), I was skeptical. But when I pulled the board out of the water wash, I was converted. Solder resist is hydrophobic, and the board came out almost dry. It was beautiful. I only use organic solvents now for spot cleaning.There are old stories of Tektronix using a household dishwasher to clean boards.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: September 22, 2023, 10:58:34 pm
content: Quote from: jpanhalt on September 22, 2023, 07:30:41 pmNot unusual at all. Small production run manufacture routinely use domestic dishwashers. I worked at one . Put thousands of boards through.

author: tooki
author_rank: Super Contributor
timestamp: September 22, 2023, 11:06:25 pm
content: Quote from: u666sa on September 22, 2023, 07:40:35 amThe white residue isnotbecause of the water. It’s salts from the reaction of the flux activators with the oxides. In fact, having more water can help remove them, because some of those salts are more water-soluble than alcohol-soluble. (But commercial flux remover is best, because the combination of solvents is more effective than any of the ingredients individually.)

author: tooki
author_rank: Super Contributor
timestamp: September 22, 2023, 11:08:34 pm
content: Quote from: jpanhalt on September 22, 2023, 10:10:21 amIn theory only. Here in Switzerland, Zep products aren’t available at retail (and even what’s available to commercial customers is a small sliver of what they sell in USA).

author: forrestc
author_rank: Unknown
timestamp: September 22, 2023, 11:18:45 pm
content: Quote from: sairfan1 on September 21, 2023, 09:18:32 pmThe care about reliability answer:Use no-clean flux and don't clean. Generally, properly activated no-clean flux has less reliability impact on a board than the residues left on a board after improper cleaning.Proper cleaning usually means using the correct cleaning solution for the flux you are using and then utilizing something dishwasher-like to ensure that it completely rinses the board, including under all of the parts.Ultrasonic can work too but the proper solutions are expensive and then you have to worry about part compatibility with ultrasonics.

author: jmelson
author_rank: Super Contributor
timestamp: September 24, 2023, 01:31:51 am
content: Well, If you MUST clean the boards, use water soluble flux. But, then you MUST clean the boards to remove the corrosive flux. The water-washable flux comes off with just a TINY amount of water, and leaves the board spotless - quite amazing! But, you really only need to do this with high voltage or high impedance boards. On normal digital circuitry, I just use no clean flux.Jon

author: Psi
author_rank: Super Contributor
timestamp: September 24, 2023, 01:57:03 am
content: For Rosin/No Clean fluxA quick (20 second) scrub with a brush in a tub of IPA followed by a rinse in cleaner IPA and then being hit with a blast from the air compressor works pretty well.The flux dissolves into the IPA and then the air compressor blasts all the IPA off the board before it has time to evaporate and leave the flux residue behind again. If you don't get the IPA off quick enough you will get white streaks on the PCB as the IPA evaporates and leaves behind flux.Note: There is some risk here, you are aerosolizing IPA which is flammable. So care should be taken.And keep a distance from the air compressor nozzle so you don't risk damaging the PCB components, or your skin, with the pressure.I always recommend two tubs of IPA, one for the scrub to get all the big chunks off, and one for a quick rinse to get all the dirty IPA off before the air compressor removes the last of it.You want the rinse step to be done with clean IPA (or at least cleaner IPA).If the rinse step is done with 100% fresh IPA you may not even need the air compressor. But using fresh IPA for each PCB is not really practical.For a more professional solution get proper flux removal solution and use an ultrasonic bath.Professional flux removal solution can absorb a lot more flux than IPA can before it becomes saturated.

author: tooki
author_rank: Super Contributor
timestamp: September 24, 2023, 08:26:19 am
content: I would add that if your intent is to clean the boards, then avoid no-clean flux, because many of them are hard to remove. Rosin flux is easier, and of course water-soluble is designed such that it must be cleaned. (Do not use water-soluble for any connections that flux can wick into and become difficult or impossible to clean, like stranded wire or many unsealed switches.)Water-soluble no-clean fluxes are now available, but I haven’t had a chance to test them yet.

author: LinuxHata
author_rank: Frequent Contributor
timestamp: September 24, 2023, 08:33:35 am
content: IPA works well with old style fluxes, but it does nothing to modern fluxes.Even if you help with brush, all your actions will just smear the flux over the PCB.Acetone works far better, and it is the main component of "flux off" and other things (just look up their MSDS)However, acetone also requires mechanical interaction (brush), which I found non-practical in case of a lot of PCBs with a lot of fine components.One that works reasonably well without brush, is Sodium hydroxide (caustic soda), but it also will hurt plastic of electronic components and might mess with enamel in inductor wires, too.I was able to get information of what do they use in big PCB factories for flux removal and while these substances are available in US only, they're industrial use, have very bad fumes and some of them are even regulated substances (Hint - name of most common used one starts with "per" (No it is not ammonium perchlorate) and it is also used in industrial clothing cleaning systems)

author: tooki
author_rank: Super Contributor
timestamp: September 24, 2023, 08:45:25 am
content: Quote from: LinuxHata on September 24, 2023, 08:33:35 amI’ve looked at the MSDSs of a bunch of (non-water-based) commercial flux removers, and almost all of them avoid acetone entirely because it’s so harsh on plastics.They are mostly blends of alcohols and hydrocarbons. Using multiple solvent types has synergistic effects that make them far more effective than any of the ingredients alone.The best way to use them is basically the same way we use Windex when cleaning glass: mop it up with wipes or swabs. A brush will only help dissolve the flux, but you must remove the flux-laden solvent.

author: LinuxHata
author_rank: Frequent Contributor
timestamp: September 24, 2023, 08:55:45 am
content: I don't know where you were looking, but I just opened the "flux off" MSDS and it clearly says acetone:https://docs.rs-online.com/95f7/0900766b803e8dfd.pdf

author: tooki
author_rank: Super Contributor
timestamp: September 24, 2023, 09:50:18 am
content: Quote from: LinuxHata on September 24, 2023, 08:55:45 amSo what?I said that almost none contain acetone, which is true. I did NOT say that NONE of them do.Looking at solvent-based flux cleaner sprays for hand use (I just checked the MSDSes of all of these), not the stuff sold in canisters for machine use, and excluding aqueous cleaners:Chemtronics alone has 8 different solvent-based flux cleaners, and of those, only 3 contain acetone, and it’s not the main ingredient in all of them. The 3 that do are the ones sold for lead-free or no-clean fluxes.Kontakt Chemie has only one flux cleaner, and it contains no acetone.Electrolube has three solvent-based flux cleaners and none contains acetone.Techspray has four solvent-based flux cleaners for manual use, and none contains acetone.3M makes one flux cleaner and it contains no acetone.MicroCare makes 9 flux cleaners and only one contains acetone.So… that’s 4 with acetone out of 26 cleaners. I think that at minimum, one can say that the vast majority are acetone-free.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: September 24, 2023, 11:47:46 am
content: Some items are best not cleaned, such as this GPS module, which is copied from the U-Blox Neo 8 hardware integration manual:---------------CleaningIn general, cleaning the populated modules is strongly discouraged. Residues underneath themodules cannot be easily removed with a washing process.• Cleaning with water will lead to capillary effects where water is absorbed into the gap between thebaseboard and the module. The combination of residues of soldering flux and encapsulated waterleads to short circuits or resistor-like interconnections between neighboring pads.• Cleaning with alcohol or other organic solvents can result in soldering flux residues flooding intothe two housings, areas that are not accessible for post-wash inspections. The solvent will alsodamage the sticker and the ink-jet printed text.• Ultrasonic cleaning will permanently damage the module, in particular the quartz oscillators.The best approach is to use a “no clean” soldering paste and eliminate the cleaning step after the soldering------------------------SJ

author: LinuxHata
author_rank: Frequent Contributor
timestamp: September 25, 2023, 10:48:32 am
content: So we have 4 out of 26, this is rougly saying, 15%, quite different from "close to none", right?And by the way, as you've observed by yourself, acetone is present in a flux removers for the modern solder paste/fluxes - where we all are going to.So as I said above, if you're old tech, stick with IPA and will be fine, but if you're into newer solder pastes and fluxes, you need to go serious.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: September 25, 2023, 10:55:03 am
content: For those in the UK, this cleaner from Farnell is very effective and cheap too. Order code 1736213.SJ

author: PlainName
author_rank: Super Contributor
timestamp: September 25, 2023, 12:49:15 pm
content: QuoteQuality, this - even has CAD models!

author: tooki
author_rank: Super Contributor
timestamp: September 27, 2023, 11:39:35 pm
content: Quote from: LinuxHata on September 25, 2023, 10:48:32 amAll the ones that contain acetone are for lead-free/no-clean, but not all flux cleaners that are for lead-free/no-clean use acetone. Most brands do them without.Anyhow, even for classic rosin fluxes, while IPA gets it all off, blended-solvent flux removers do a better job, in that they dissolve it much faster, and without needing as much solvent. IMHO the reduced time and effort make it worthwhile.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: September 28, 2023, 05:36:36 am
content: Quote from: tooki on September 22, 2023, 05:24:01 amI started this way, butI found I was spending more on cotton swabs than flux cleaner and getting poorer results.

author: LinuxHata
author_rank: Frequent Contributor
timestamp: September 28, 2023, 07:41:41 pm
content: I talked to my grandpa, and as he says, in the "good ol days" they used a boiling acetone(!) to remove all flux and greasy residues from the PCB, but only if it contained no plastic parts. Since process was quite dangerous, they later shifted to "less dangerous" mixture, which contained equal portions of acetone, methyl ethyl ketone, tetrahydrofuran and cyclohexanone. Still, can't be used on most of plastics. However, I think I'll give a try to it, since it is currently commercially available in US in almost any brick and mortar store and is called PVC pipe primer.

author: jpanhalt
author_rank: Super Contributor
timestamp: September 28, 2023, 09:08:31 pm
content: Those solvents will do it, but a bit safer is alkaline (for "saponification") plus butyl cellosolve (10%) with water in an ultrasonic. I am an 80 yo grandpa myself, and I had to do it to believe it.

author: MathWizard
author_rank: Super Contributor
timestamp: September 29, 2023, 01:53:44 am
content: Quote from: twospoons on September 22, 2023, 07:24:27 pmThese days I use a toothbrush and hot soapy water. Cheap and easy, I try not to use the kitchen sink, but I do sometimes with little proto-boards. Then I rinse them in hot water, dry them off, sometimes with the vacuum, then leave them on a radiator to dry.But sometimes I still need to use IPA before, or after, 1 of my fluxes leaves a conductive residue, ans soap doesn't always get it.