How to Remove White Residue on PCBs - Page 1
Forum section: electronics / general

author: bostonman
author_rank: Super Contributor
timestamp: November 14, 2021, 05:29:53 pm
content: Over the years I've tried cleaning boards without luck.Obviously flux residue doesn't come off easily and needs to be plucked off, but, once I clean with Isopropyl, I still get white residue once dried.At old jobs I'd leave the boards soaking in a isopropyl pan, I'd go over the board with a brush several times, etc... and then blow air to dry off the isopropyl.Recently with home projects I've tried the electronic spray, but that too leaves white residue. I'm assuming the flux in the solder (and any added) gets dulled by the isopropyl, spreads out, and dries.Does anyone have a trick to getting a board clean because I've been frustrated over this for years.

author: jmelson
author_rank: Super Contributor
timestamp: November 15, 2021, 12:30:11 am
content: Soak with isopropyl, then brush with an old toothbrush, then immediately wash with water, you will see a white cloud in the water, that is your while residue being washed away. You may have to repeat several times to get it completely clean.OR, use water-soluble flux where the boards NEED to be cleaned, it is amazing how clean they come out after just a water rinse. No solvent needed.Jon

author: all_repair
author_rank: Frequent Contributor
timestamp: November 15, 2021, 12:40:35 am
content: After cleaning off with alcohol or flux removal solution, I rinse with distilled water to flush away any leftover liquid.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: November 15, 2021, 12:51:09 am
content: I just use iso and scrub with the toothbrush till its all looks clean when wet.Rinse the board by orienting it vertically and then squirting copious amounts of iso on onto it. A small river of iso should flow off the pcb.You probably could use other liquids for rinsing but iso is not that expensive.

author: Bud
author_rank: Super Contributor
timestamp: November 15, 2021, 01:16:39 am
content: A trick that worked for me (someone posted here a few years ago) was to use Spay Nine cleaner instead of isopropyl (for no-clean SMT flux, not rosin flux) . And a toothbrush of course. Rinse with demineralized water after.It might also work as a second step after cleaning with isopropyl first but i did not try.

author: jpanhalt
author_rank: Super Contributor
timestamp: November 15, 2021, 01:41:29 am
content: Ironically, this thread comes just when I was removing "white residue" from a PCB. For a little background, I have been experimenting with cellosolves as flux removers. Later, I found that some commercial removers also contain them. What limited me was finding a board that had white residue as a positive test.I use 63/37 flux cored Kester solder with 44 flux and rarely had a problem removing it cleanly from freshly soldered joints on PCB's with absolute ethanol or absolute ethanol/acetone 3:1 (very approximately). I settled on testing ethyl cellosolve (2-ethoxy ethanol), because it can be dried easily and quickly with compressed air. It works neat and almost as well with considerable water (up to 20%). The board I was working on today was a SparkFun solderable breadboard that was a few years old. The red solder mask made seeing any residue easy, and I was got a white residue with ethanol.Then, I used neat ethyl cellosolve. It removed the residue completely, but there was a slight haze on a few areas of the solder mask and some connectors after blow drying at room temperature. A rinse in absolute ethanol gave a nice shiny board with no haze.I don't know whether the slight haze was from impurities in the cellosolve (technical grade) or something on the board. The rinse in ethanol removed it quickly. My ethyl cellosolve was bought over eBay from an American source. It was manufactured by HyMedia Laboratories (India) and was reasonably priced for 500 ml. That class of solvents is widely used and relatively non-toxic. The characteristic odor of some floor cleaners (e.g., ZEP stripper) is due to butyl cellosolve. The board ended up needing rework, and for cleaning that, I started with neat ethyl cellosolve, which worked fine.My procedure going forward will be a wash in ethyl cellosolve using a toothbrush to get into crevices, let drain, rinse in ethanol, and blow dry.

author: bostonman
author_rank: Super Contributor
timestamp: November 15, 2021, 02:20:04 am
content: I've left boards soaking at my old jobs (they had large containers to hold entire PCBs) and they'd still have white residue.I'll try the other ideas, but seems water can be dangerous for boards that have plastic switches and stuff.

author: andy3055
author_rank: Super Contributor
timestamp: November 15, 2021, 02:46:21 am
content: What kind of solder are you (OP) using? I use 60/40 rosin cored solder and I have no problem removing it with (even) 70% alcohol that you can buy at the drugstore. You have to do it a few times to get rid of the stickiness but it can be done. If you have a tray filled with alcohol and dip the board in it and use a brush, it should work.

author: Whales
author_rank: Super Contributor
timestamp: November 15, 2021, 03:01:16 am
content: Apparently white PCB residues can be caused by a lot of different chemical products, not even necessarily all from the flux:https://www.kester.com/Portals/0/Documents/Knowledge%20Base/White-Residue-15Apr1988.pdf

author: Rat_Patrol
author_rank: Frequent Contributor
timestamp: November 15, 2021, 04:32:52 pm
content: For SMT or THT?For THT, I use water wash flux solder and flux paste. Washes right off easily.For SMT, I still use standard no-clean flux from Chipquik, but I soak in a vat of IPA for 10 minutes, 5 minutes in the ultrasonic cleaner with Branson EC, rinse with DI water, and they are squeaky clean.

author: asmi
author_rank: Super Contributor
timestamp: November 16, 2021, 03:03:29 am
content: I use ultrasound washing machine. Highly recommend! If you do not tolerate high-pitched sounds well, cover it with some box while it's working.

author: bostonman
author_rank: Super Contributor
timestamp: November 16, 2021, 05:17:56 am
content: QuoteSee attached. This is my stash, but at other jobs, I'm sure it was other types of stuff and I didn't have much luck cleaning.QuoteThe type of boards/parts has been a combination of through-hole and SMT along with boards that were repaired with parts that (probably) can't get water in them because they are not sealed; so I'd be reluctant to put water on these types of boards.Do you have a ultrasound washing machine model recommendation? Again though, if a board has things like DIP switches or parts that can be damaged, would water be the best solution?At an old job we had (over the course of years) hundreds, if not, thousands of power supplies fail in units because it was determined that whatever the board house used to clean the boards was getting up the leads and into the capacitors causing them to short internally. I don't know if it was limited to water or the capacitor was cheap allowing water/alcohol (or whatever cleaning solutions are used) to get inside.

author: jpanhalt
author_rank: Super Contributor
timestamp: November 16, 2021, 02:14:23 pm
content: UPDATEI have finished the prototype I was working on (post #6) and only used ethyl cellosolve to clean up after revisions. So far, it has worked well with the 44 flux residue. I have attached a couple of pictures. I tried to get reflections in one, but was not very successful. The cleaned boards are as shiny as when I use absolute ethanol or ethanol/acetone. No white residue was noticed.The current Kester 5768 flux remover has ethanolamine and diethanolamine in it. It is sold as a concentrate for dilution with water. The amines are to provide "saponification," which Kester says is necessary for its newer fluxes. I suspect one could try those with ethyl cellosolve and a little water. Maybe simply adding some household ammonia would work too. Apparently, Kester 5768 cannot be shipped to home addresses by a local distributor.

author: asmi
author_rank: Super Contributor
timestamp: November 16, 2021, 03:11:00 pm
content: Quote from: bostonman on November 16, 2021, 05:17:56 amI wash all my boards, with all connectors, switches, buttons, etc. Never had any failures. I've bought a cheap 6L machine on Amazon, as for the solution, I use BM-5000 General Purpose Ultrasonic Cleaning Solution Concentrate also bought there. This solution is 92% Ethanol, I dilute it 1:10 with distilled water as per instructions, and results are very good - importantly, matte PCB soldermask looks pristine again after washing, something I was never able to achieve using any "manual" methods.Once out of the wash, I usually either leave them in the open for at least 24 hrs to dry naturally, or put them in an oven at 50-60°C for 1-2 hrs if I want to begin testing boards ASAP. Theoretically one could use a hot air gun set to the 100°C to dry it even faster, but I don't think that's a good idea because moisture + heat + temperature gradient across the PCB is not a good combination.Most parts are designed to withstand US wash because they are often used at PCBA fabs, but there are some which are not. These are usually components that have intentional openings in the package - like pressure sensors, or humidity - that sort of thing. But since none of the boards I washed had them, so I don't really know details.Also ultrasound wash acts as a good test of soldering quality due to mechanical stresses induced, so be prepared for some of your tombstones you didn't notice to detach. It happened to me few times, but isn't that often even though I use cheap ZB2520HL reflow oven and not some sort of "professional" one.

author: bostonman
author_rank: Super Contributor
timestamp: November 17, 2021, 02:12:28 am
content: I'll have to look into some of these options.I agree that some boards are safe to soak, but I had a board from an Agilent scope with 0603 parts, ZIF connectors, tiny fingers that held RF shields (a complete nightmare to reattach the shields), and double sided. I imagine the board would need to be placed onto something so the bottom side of the board doesn't rub causing components to break. This board, however, looked like it had borderline solder connections because I had to replace the ZIF connector and found the pins basically pulled off the solder. This cleaning method would possibly cause many issues.Trying to clean this board was a nightmare. The tiny fingers that hold the RF shields kept grabbing the acid brush hairs and ripping them off. The board ended up having numerous hairs stuck everywhere.The current board I've tried cleaning is from a C64. This is certain more durable than the Agilent scope board, however, it has a sensitive RF section, a plastic power switch, and plastic connectors. Not to mention I don't know how well sealed the components are (although I've replaced just about all the electrolytics).The main thing I don't understand: I've used over a half can of contact cleaner, several amounts of isopropyl (with the board on its side in both incidents so the liquid runs down/off the board), and, instead of letting the remaining stuff sit, I'll use a vacuum cleaner to suck all the liquid off (I don't have an air compressor and figure it basically performs the same function).After several cycles of the above method, I still saw white flaky residue. My thought is that the isopropyl and spray should drag all the junk to the bottom of the board. This doesn't seem to be the case as I find the white flaky stuff everywhere.Maybe I shouldn't use contact cleaner and use some sort of flux spray cleaner?The irony is that I've used brake cleaner, carburetor cleaner, and the contact cleaner, all on various stuff. In most cases, depending on what I'm cleaning, and what I'm using, the cleaner always seems to leave the item shining. Yet, something so simple as flux seems to be a nightmare to remove.

author: bostonman
author_rank: Super Contributor
timestamp: November 07, 2023, 02:55:37 pm
content: I'm resurrecting an old thread that I originally started.Recently I repaired a vintage Commodore mouse with plastic mechanical parts. Due to the plastic and age, I was reluctant to use anything but Isopropyl alcohol. As usual, I grabbed a brush (tooth brush this time), dipped it in the Isopropyl alcohol, and scrubbed all the flux. After drying, not only was the section I brushed white with flux residue, but spread to other areas.I repeated the wash and got it cleaner, however, some was still sticky. The only thing that seemed to work was using a can of air to wash off the alcohol and dry it quicker.If I remember correctly, back at my old job I'd leave a PCB submerged in alcohol, scrub it clean, and would still see white residue after it dried.My assumption would be the Isopropyl alcohol is strong enough that it deludes the flux, scrubbing it clears it away, more fresh alcohol, eats the remaining, and then another dose of alcohol, and it dries clean.This doesn't seem to be the case. My confusion is what am I doing wrong, and, also, I'd like to put a few bottles of Isopropyl alcohol in a metal pan to wash boards in the future but sometimes the alcohol mixes with the metal and causes the alcohol to become mixed with metal tarnish residue.Does anyone have recommendations for a pan and ways to stop my boards from remaining white/sticky?

author: jpanhalt
author_rank: Super Contributor
timestamp: November 07, 2023, 03:47:12 pm
content: Try the acrylic floor stripper mentioned below. I use ZEP brand Heavy Duty Floor Stripper which is butyl cellosolve, a little ethanolamine for saponification, and water. You want a final cellosolve concentration of about 10%.Oops, I just noticed the date. I switched from messing with other cellosolves to just using the cheap stuff, because evaporation is not an issue.

author: luudee
author_rank: Frequent Contributor
timestamp: November 07, 2023, 04:04:12 pm
content: I usually use Acetone and Q-tips.That works very well for me. Obviously have to take special care with Acetone.Cheers,rudi

author: thm_w
author_rank: Super Contributor
timestamp: November 07, 2023, 10:21:42 pm
content: Quote from: bostonman on November 07, 2023, 02:55:37 pmWas this just cleaning, hot soapy water works for that. Windex is another good one to try.If the flux has been there for 40 years its probably harmless at this point.

author: bostonman
author_rank: Super Contributor
timestamp: November 08, 2023, 12:31:09 am
content: QuoteNo, this flux was due to a repair.As mentioned, I am sure many of these chemicals will work since many of you had such luck, however, what I find is that boards I repair contain plastic hardware, or something that always forces me to question whether I'll ruin parts as a result of using harsh chemicals.In all my jobs, everyone uses Isopropyl alcohol and seems to have better luck than me. From what I see, if I place a paper towel over the washed area (let's ignore the static electricity issue) and then use the brush to absorb the liquid by pushing the brush down on the paper towel and/or air blow (in my case I've used a vacuum cleaner since I don't have a compressor but always afraid I may suck a part off the board), it seems to dry much cleaner; but usually still somewhat sticky.

author: jpanhalt
author_rank: Super Contributor
timestamp: November 08, 2023, 12:52:51 am
content: Well, if you use IPA and it works, great. If it didn't work, as seems to be the case, keep repeating it. Maybe your luck will change.My advice is, if IPA didn't work, try something different. You seem to think IPA is less harsh than consumer floor cleaner diluted 1 part to a total volume of 3 parts.. Why? What do you mean by "harsh?" How is it measured?

author: bostonman
author_rank: Super Contributor
timestamp: November 08, 2023, 01:59:28 am
content: I've used a few things over the years for cleaning (not PCBs) such as brake cleaner and either electronic cleaner or intake manifold cleaner, and sometimes it ruins the plastic.For the most part, I've never had IPA ruin anything and would assume letting the PCB sit in a IPA bath would clear away everything. I know that in the past I've poured IPA into a metal pan only to find it got discolored with mixing with whatever metal the pan was made from. So I was wondering what a safe metal pan would be to avoid this.

author: thermistor-guy
author_rank: Frequent Contributor
timestamp: November 08, 2023, 04:35:06 am
content: Quote from: luudee on November 07, 2023, 04:04:12 pmArctic Silver makes ArctiClean:http://www.arcticsilver.com/arcticlean.htmIt's great for removing thermal grease. It might be useful for PCB residue removal.

author: wilhe_jo
author_rank: Regular Contributor
timestamp: November 08, 2023, 08:06:02 am
content: At least for me, the residues are partly cased by my IPA.Switching to 99% stuff (IIRC the old one was 80% or so) made it way better, but not perfect.What works best for me for "smart front panels" (front panels made from PCBs with cap-sensors, LEDs,... On their back) is the following procedure:- get it clean with IPA- wipe with fresh IPA- wipe with rs-components quick dry cleanerThis cleaner by rs-components smells suspiciously similar to break-cleaner. Which makes sense, because it would desolve a different type of residue.73

author: Psi
author_rank: Super Contributor
timestamp: November 08, 2023, 08:13:51 am
content: IPA is annoying for cleaning flux, it gets saturated with flux residue almost immediately and then leaves white streaks on the 2nd or 3rd PCB you clean with it.You will find it works much better if you have 2x IPA tubs for dirty and clean IPA.Give the PCB a good wash and scrub with a brush in the 'dirty' IPA tub .Then do a final rinse in the fresh IPA tub. Rinse only though, don't scrub in the rinse bath or you will dislodge more flux hidden under ICs and create streaks again.Then immediately blow the PCB clean with compressed air before the IPA has a chance to evaporate and leave flux behind. (Be very careful with this step as you are aerosolizing a flammable liquid).After you're done with cleaning all the PCBs, make your clean IPA becomes the dirty IPA for next time.And when you next use it you pour some fresh IPA into the clean IPA tub.

author: jpanhalt
author_rank: Super Contributor
timestamp: November 08, 2023, 11:07:50 am
content: Quote from: bostonman on November 08, 2023, 01:59:28 amYou have to look at the chemicals involved, not what some marketing person calls it. For example, I have 2 types of brake cleaner on the shelf. One is virtually pure TCE (tetrachloroethylene/perchloroethylene/PERC) the other is labeled "non chlorinated" and has methanol, acetone, toluene, ethylbenzene (related to toluene) and various short-chain hydrocarbons. Those are quite different. PERC is relatively insoluble in water (0.015% or 0.15g/liter) ; acetone and methanol are miscible with water. There are both designed to remove oils. Neither is designed for flux; although, I suspect the non chlorinated version would be better.QuoteAlcohols show a striking difference in solvent properties when water is added. Absolute ethanol is great for fats; 95% is not so good As for your metal pan, IPA is not known to attack vigorously common cooking pans. Of course, magnesium and lithium are not used for cooking. Under some conditions, aluminum might react a tiny bit. I suspect your observation is simply related to removing some cooked on residues.Cellosolves are an ether and alcohol in the same molecule (e.g, alkoxy glycols). Alkoxy describes an ether linkage (R-O-R'); glycol describes a molecule with two hydroxy (alcohol) groups (e.g., ethylene glycol [https://en.wikipedia.org/wiki/Ethylene_glycol ]). Diethyl ether (a simple ether) is a good solvent for oils and some fats but not polymers.It's the combination of the two classes that gives cellosolves their unique solvent properties. That is, water soluble and dissolves oils, baked on oil, polymers (e.g, acrylic wax) and so forth. In their pure state, they attack paint and are used as paint solvents, but adding water diminishes that effect. The recipe I gave is the same composition as Kester's newer, water-based flux removers.I use it in an ultrasonic for 2 minutes, then rinse under running water, and another 2 minutes with DI/distilled water to get rid of any remaining salts.You are worried about the effect on plastic. That is hard to predict. Some solvents may not seem to attack the plastic right away, but months to years later cause crazing.And alternative is a kitchen dishwasher with common dish detergent. It is reported that name brand manufactures, e.g., Tektronix, used a dishwasher in its repair area.Lastly, just live with the white residue.

author: bostonman
author_rank: Super Contributor
timestamp: November 09, 2023, 03:38:37 am
content: Personally I think leaving white residue behind looks ugly, and, in high frequency circuits, thought it could cause issues.In any case, my feeling is simply that white residue gives the impression the job was done half fast. In almost all cases, anything I've fixed is something I care enough about to not experiment with and/or has components that may not be sealed along with mechanical plastic parts.My plan several months ago was to get some sort of pan, pour four or five bottles of IPA in it, leave the section of PCB with the flux residue soaking, and then clean with an acid brush. These are the steps I took at my old job and seemed to still have residue remaining. As a previous post suggested, I use one pan as the "dirty" IPA and a second pan with "clean" IPA. While this may work, it certain will eat up quite a bit of IPA bottles.The way I do it now, and maybe this is the issue: I keep a bottle of IPA (maybe 10-12oz bottle) nearby along with acid brushes and a tooth brush. Usually I turn the PCB sideways, scrub with the brush(s), dunk the brush in the IPA again, scrub more, and let air dry.I've planned to buy an air compressor just so I could blow off the alcohol as using a can of air seemed to have better results.One thing I don't understand is why the flux doesn't get burned off during soldering. It seems a dab of solder results in a puddle of flux many factors more than the dab of solder used.

author: Ian.M
author_rank: Super Contributor
timestamp: November 09, 2023, 05:48:28 am
content: That's seriously sub-optimal as IPA is hygroscopic, so if exposed to the air for an extended period, dilutes itself with the moisture in the air and as the water content increases, it passes a threshold and tends to drop the dissolved rosin out of solution leaving whitish gooey residue.By all means, pre-soak in your tray of used IPA to soften the deposits, but to actually wash them off you need fresh dry IPA applied by spray or brush, sufficient to run off the edge of the board into your catch tray, + usually a fair bit of scrubbing. After the final IPA rinse put the board on edge on kitchen towel to let as much as possible run off and to blot the edge to prevent droplets forming and drying to leave sticky patches.Also, to keep it as dry as possible, try to avoid opening your stock IPA bottle frequently by dispensing into a smaller well stoppered container for bench use, no more than can be used in a couple of weeks, and keep the bench container tightly stoppered when not in use.Ionic residue (metal salts from flux action) can also leave white deposits, and the water in somewhat dilute IPA helps remove them but if the IPA is wet enough to precipitate rosin, it cant get to the metal salts embedded in the rosin.

author: jpanhalt
author_rank: Super Contributor
timestamp: November 09, 2023, 05:49:47 am
content: Have your not seen the Kester paper on white residue?https://www.kester.com/Portals/0/Documents/FAQs/White_Residue.pdfAlso look up the SDS for Kester 5768 and its other water-based flux cleaner.You say you don't want to experiment with the meaningful boards, yet that is exactly what you are doing. You have tried IPA. It didn't work. So, now you seem to want to keep trying insignificant variations until it works. Never say never.Kester is a pretty well known name in the business. It has already researched the subject. Its discussion of the problem makes sense, and my personal experience is consistent with that. My usual method until I switched was absolute ethanol with or without a little acetone. I tried IPA and found absolute ethanol faster and better.On a recent PCB with a TQFP 44 chip, I could not get the residue completely off. Board didn't look bad, but between the pins there was the precipitate. So I tried the Kester formula, and it was like magic. The attached picture was taken about a year later so there is some dust and lint on the board. As for how to dry the board? When taken out of the wash bath and rinsed with water, the board was effectively dry. Solder resist is also water resist. It is quite hydrophobic when clean.IPA is miscible with water. Why do you need an air compressor to blow it off? If it is clean, it should just evaporate without leaving a residue. If it is not clean, then get some that is. Lack of an air compressor is not the problem. Have you considered a water rinse to remove slightly contaminated IPA?Anyway, you seem to ask questions for information, then argue against any suggestion that is contrary to your original plans. I have given you the best advice I can and will be moving on. BTW, soaking in IPA may not be the best thing long term for some plastics. It may remove plasticizers without causing any immediate effect, but long term, the plastic may show crazing or be more brittle.

author: Ian.M
author_rank: Super Contributor
timestamp: November 09, 2023, 05:54:55 am
content: Chemtronics' notes on the subject are also worth a read:https://www.chemtronics.com/the-dreaded-white-residues-why-they-form-what-to-do-about-them

author: zapta
author_rank: Super Contributor
timestamp: November 09, 2023, 08:21:50 pm
content: I use isopropyl with a brush and cleanroom micro fiber wiperss to lift the dirt. (Kimwipes are terrible for this application, making the entire board wipe).https://www.aliexpress.us/item/3256805873860950.htmlIf I have larger cleanup jobs or multiple boards, I use an ultrasound cleaner, Branson EC Formulated Cleaning Concentrate and distilled water, and the result are great. You can find instructions on youtube, e.g. make sure to degass the solution.https://www.amazon.com/gp/product/B071FBGMLC?th=1Another option is to just use white PCBs. ;-)

author: zapta
author_rank: Super Contributor
timestamp: November 09, 2023, 08:26:18 pm
content: Quote from: bostonman on November 09, 2023, 03:38:37 amI got this one for the same exact purpose. It's mains operated, very powerful, and does a great job. There are many others, including rechargeable battery operated.https://www.amazon.com/gp/product/B0BN16MWVS

author: bill_c
author_rank: Regular Contributor
timestamp: November 09, 2023, 09:56:07 pm
content: Cold ultrasonic and / or isopropyl alcohol usually leaves white residue for me, hot ultrasonic and denatured alcohol solved it for me. I do like the floor stripper idea though.

author: bostonman
author_rank: Super Contributor
timestamp: November 10, 2023, 03:28:49 am
content: QuoteDidn't think I was "arguing". I was simply elaborating on the processes I've tried and asking any similar suggestions to further explain since part of the steps were similar steps I took.From what I can tell, many cleaning variations exist and I need to re-read the suggestions in greater detail along with reading the links provided.If I felt the need to argue with advice, I wouldn't ask for advice in the first place. I'm somewhat active on here, and have had some great help with my projects. White residue has annoyed me, and I wanted to emphasize that some of the boards I've worked on aren't simply components, but an assortment of hardware and components I question whether they are safe to drown in cleaning solvent.

author: smh
author_rank: Newbie
timestamp: November 12, 2023, 03:16:08 am
content: Out of interest, are you trying to remove the white residue because it aesthetically doesnt look very nice, or does it have an adverse affect on the pcb/components? (or both!?)

author: bostonman
author_rank: Super Contributor
timestamp: November 12, 2023, 03:43:07 pm
content: A combination of both along with having not known what the white residue could do to components over time.From this thread, it seems the white residue won't do much harm, however, I believe at high frequencies (which I haven't had any to repair recently) could cause impedance issues.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: November 15, 2023, 02:05:20 am
content: From what i discovered on youtube, cleaning a stain is a two part process.I think you have only done one part.1. Dissolve the white residue.2. Remove the dissolved stuff from the pcb.I do step 1. by cleaning and dissolving the residue with IPA and a toothbrush.Then for step 2.Flood the still wet pcb with IPA via a pump atomiser.Keep pumping for a while, keeping a steady flow of liquid running off the edge of the board.Sometimes i may use IPA mixed with water, not sure why.

author: bostonman
author_rank: Super Contributor
timestamp: November 22, 2023, 03:51:24 am
content: I had some time and reread this thread along with the links.A few questions.Some suggestions were warm soapy water. I know water eventually evaporates, but I want to confirm that (literally) warm water from the faucet along with a mix of (assuming) Dawn dish soap. This is safe for things like surface mount ICs where the water may seep underneath the IC and take long to evaporate?If this method works, it's a great suggestion and a cheap solution; but the drawback I'd assume is the wait time for drying before power can be applied to the board; unless I use a mini oven to dry the board (but then I run into issues with any plastic pieces on the board).Ultrasonic (one person suggested warm ultrasonic) seems really cool, but can/will this loosen components and/or possibly crack any mechanical parts? I don't know anything about ultrasonic cleaning or "heated" ultrasonic, but I think being able to use such a unit to clean boards would be cool.I do like those air blower guns and plan to purchase one on (Black) Friday. This certainly beats a compressor, but a bit of a concern for old boards where weak solder joints may result in components blowing off (I'm just thinking out loud as I've given thought to using air in the past).Finally, Flux Off seems like a good solution. A bit expensive, but well worth the cost if it cleans the flux - I may also add this to my list of stuff to buy on Black Friday.

author: CurtisSeizert
author_rank: Regular Contributor
timestamp: November 22, 2023, 05:08:29 am
content: In my experience, the solution to this is not so much in the cleaner as it is in the choice of solder paste. The residue from "no clean" type solder paste is difficult to get off. I have switched to using water washable solder paste, and it's not an issue anymore. For flux I use RMA. Both residues are easily removable with IPA, just a little brushing and rinsing required. To get the IPA out from under IC packages, etc., I use a battery powered duster for cleaning keyboards, etc. that I got on Amazon for $50 or so. For fA circuits, I would probably spring for HPLC IPA, but "ACS grade" from Amazon is fine at the single digit pA level. Perhaps there will be a Black Friday deal. I need to restock. Post cleaning, I usually bake between 75 and 125 C for an hour, but sometimes I don't bother if I am reworking a prototype. The ADA4530-1 datasheet has some information about solder pastes and cleaning.I am an organic chemist by training, and I have no problem using more aggressive solvents, but they all present a waste disposal concern. This may be no problem if you are a company and you have a contract with another company who will take the stuff away, but in my house, my preference is to avoid generating hazardous waste streams where possible. I do use the various canned flux removers if I am in a hurry and don't feel like cleaning the whole board. The hygroscopicity of IPA is not a real concern if you're turning it over and closing it when not in use. It forms a good azeotrope with water, so the liquid phase left behind as it dries will decrease in moisture content. This is a property I have exploited many times as a chemist to reduce the moisture content of non-volatile products. If you are going to use an aqueous cleaning solution, I would wash with DI water and rinse with IPA.If for some reason you are in a situation where you have every available solvent and need to clean a stubborn organic residue off, THF is unbeatable. It is the source of that distinctive smell in the purple PVC primer, and it will go through 6 mil nitrile gloves in about 3 seconds.

author: bostonman
author_rank: Super Contributor
timestamp: November 23, 2023, 12:21:12 am
content: I agree that solder paste and flux is probably the start and a good one makes cleaner easier.QuoteI think this summarized what I've seen best and explains quite a bit. Often times I've soaked the area with IPA, brushed and brushed, and thought, this is it, the board should be clean. Later I look, and the board looks horrible.I plan to buy a can of flux off, but will also work on some methods listed.Most likely much of this is my fault because I had a similar issue with paint brushes recently. I used oil based paint, and, to clean the brushes, I was told to use paint thinner. Well, I poured paint thinner in a pan, put the brush in it, pressed the bristles, turned, etc... The next day the bristles were still moist, the day after the bristles were hard.I thought it was just them being dried, so I manually bent them until they soften and used the brush again. Used the same cleaning method, and the same issue occurred. Eventually I returned to the store to discuss the issue and was told to use one "dirty" pan and one "clean pan", so I bought a new brush. I told the guy I'll buy a fresh can of paint thinner and he said the one I have will be perfectly fine.Afterwards, I did the method he described, and I still have the same issue happening with the bristles. So it's obvious I'm not following the methods correctly and probably why my PCBs get white stuff when they dry.Is an ultrasonic cleaner safe for boards or can it cause the components to vibrate lose from the solder connection? I think having an ultrasonic cleaner would be pretty cool, but not sure if it's worth it.

author: CurtisSeizert
author_rank: Regular Contributor
timestamp: November 23, 2023, 04:58:48 pm
content: Quote from: bostonman on November 23, 2023, 12:21:12 amWater absorption from bulk IPA is an unlikely root cause because the effect is likely to be minimal. Even in a PE bottle, I would be surprised to see moisture content rise 1% over 12 months. It is routine (if not best-practice) to put a feed line in a ventilated IPA bottle on an HPLC system and leave it there for months at a time (especially in academic labs). This is a system where moisture ingress into the IPA would cause drift in the results over the lifetime of the bottle, but I haven't seen this causing issues. I use the same IPA over and over for a pre-clean of boards right after they cool from being reflowed, and I haven't seen a case where this seems to be happening. It is possible that it happens to some extent while drying the boards, but you can fix this by rinsing the board with fresh IPA before blowing it off. This sort of moisture ingress is a problem mostly either when you are dealing with things that are much more sensitive to moisture (i.e., smaller effects matter) or when you are using solvents with a high vapor pressure because the surface of the solvent is cooling from evaporation and creating areas of high local relative humidity near the surface of the liquid.I have seen the same effect you describe with no-clean paste/flux and IPA, and I think it is more likely that under IPA the residue becomes transparent the way that salt crystals become transparent when you drop them in water. I had originally thought that this was from the residue dissolving and those places being rinsed insufficiently, so I cleaned some specific areas between the leads on an SO8 package with a dental pick and cleaned the board again in IPA. The places I had cleaned stayed clean, and the others stayed dirty. Sonication in IPA at up to 40 C, even with long exposure times (1 h) did not solve the problem for me. Most packages are OK with sonication, but best practices are to avoid sonicating quartz crystals. There were two solutions that did an OK job with no-clean flux that I found. One was using a flux remover from Chemtronics that seems to have been discontinued (probably due to VOC regulations, I think it used something halogenated from them smell), but they have other products that are targeted at no-clean flux. For me, this took multiple cycles and a lot of brushing. The other was to boil boards in IPA for about 10 minutes. I would not recommend the latter as it presents a fire hazard, but it was pretty clear that the flux residue is minimally soluble in IPA because even at boiling it tended to flake off and sink to the bottom without going into solution.I believe you will find if you switch to water washable paste and flux that this is not an issue anymore and all the more extreme solutions are unnecessary. I banged my head against the wall with this for some time and have spent too many hours trying to clean flux residue just to find out that "no-clean" means "don't clean". With no-clean paste, you may be able to avoid white residue by curing in the oven at 150 C for some time after reflow, but I haven't tried this. Also, last I checked, Amazon only has no-clean paste in stock, and you'll have to go to a proper distributor to get water washable stuff. If you're on Amazon, though, you may invest $30 in a Peltier fridge to put your solder paste in. It'll get you down to about 6 C and extend the life of your solder paste.The leaded paste I use is SMD4300AX250T5 and the lead-free is SMD4300SNL250T5. I have had good results with both cleaning with a brush in room temperature IPA.

author: tooki
author_rank: Super Contributor
timestamp: December 01, 2023, 01:52:58 pm
content: Quote from: bostonman on November 07, 2023, 02:55:37 pmFirst of all, it's important to distinguish between sticky residue and white residue, because they're very different things. (They can occur alongside each other but are not the same thing.)Sticky residue is, plain and simply, leftover flux. Thin layers of it dry glossy.White residue is the result of chemical reactions in the flux during soldering, producing ionic contaminants that are not solvent-soluble. (This is oversimplified, the Chemtronics document linked above goes into more detail.)Sticky or glossy residue is removed by simply cleaning longer. If you're submerging the boards, let them dwell longer. I sometimes just wet the board in solvent, and place it into a ziploc bag together with a paper towel soaked in the same solvent. This prevents the solvent from just drying off right away.White residues won't go away anywhere near as easily, because the entire problem is that they aren't soluble in the solvent being used.Regardless, what seems missing from all of your cleaning regimens is actuallyremovingthe residue-laden solvent. It sounds like you think solvents destroy the residues, but all they do is mobilize them. If you use solvent to dissolve the residues, but just brush them around the board, they're not actually gone, they'll just be spread out once dry. Similarly (and reiterated in your paintbrush story) soaking in solvent simply dilutes the residues, but whatever solvent is left on the board (or brush) still contains residues. You have to remove the residue-laden solvent if you want to remove the residues. Otherwise you're just moving them around and redepositing them elsewhere.(This reminds me of people who mop their floors in a single pass, without going back with clean water and a well-squeezed mop afterwards. Sure, the mop has picked up some of the dirt into the bucket, but you're also leaving behind a film of dirty water everywhere. Unless you actually lift that dirty water away, you're depositing dirt and soap everywhere.)I have mostly moved away from cleaning PCBs by drenching with copious amounts of solvent. Instead, I use a brush dipped in solvent to scrub an area of the board, then use this brush (the "dirty" brush) to mop up the residue with a kimwipe (or other lint-free wipe). Stubborn areas may require this step to be repeated. Do this for the entire board until there is very little residue. If you have an air compressor, blow out underneath chips, too.Then take a fresh wipe, lay it onto the board, and take a second brush (your "clean" one) dipped in clean solvent to mop it clean. In essence, think of how you use Windex and paper towels to polish a window. The "clean" brush's purpose is really just to let you manipulate the wipe, since our fingers are much too fat to be of use.If, after all this, your board exhibits sticky or glossy residue, then your cleaning was simply incomplete and needs to be redone. But if it exhibits white residue (and no sticky/glossy residue) after drying for a few hours, then you need to find a different solvent.

author: tooki
author_rank: Super Contributor
timestamp: December 01, 2023, 02:22:29 pm
content: Quote from: bostonman on November 12, 2023, 03:43:07 pmRead the Chemtronics link again; depending on which type of white residue it is, it can lead to galvanic corrosion and dendrite growth.Quote from: bostonman on November 22, 2023, 03:51:24 amYes and no. Hot tap water is fine as tour wash water, but not as the final rinse. You should rinse with distilled/deionized (DI) water, and ideally follow with an IPA rinse to help the DI water dry quickly. Use your compressed air to help blow it out from under chips and connectors and stuff.Water-soluble fluxes should be fine with no detergent at all, or dish liquid if you want. But non-water-soluble fluxes are untouched by dish liquid. You need a proper saponifying PCB cleaner (like Safewash) or equivalent "hack" (like Zep floor stripper, which apparently is chemically practically identical). I wouldn't be surprised if some household cleaners worked, too, but I don't have any suggestions.Unfortunately, Electrolube just discontinued Safewash in the aerosol can. Now you have to buy canisters of it.Quote from: bostonman on November 22, 2023, 03:51:24 amLoosen components?!? Maybe if you left a board in for hours and hours instead of the 3-5 minutes it should take. Ultrasonic PCB cleaning isn't a hack, it's a well-established process for which there exist dedicated chemicals and machines. The well-known restrictions are quartz crystals, as well as any components that cannot be submerged, like many types of sensors and switches. If you go ultrasonic, check the component datasheets to make absolutely sure they don't prohibit ultrasonic cleaning! (Some parts, like many environmental sensors, do not allow cleaning of any type because any liquid ingress will kill it. Some are OK with careful manual cleaning with the sensor hole taped over, others not even that. You have to check datasheets and application notes.)Pro tip for ultrasonic: to avoid having to fill the entire machine with your solvent (which is dangerous to do with flammable solvents like IPA), fill it with water, and then put your PCB into a small container (for example, a beaker) filled with your solvent, and place that into the ultrasonic bath. You can also use ziploc bags to the same effect. (Some recommend double-bagging.)Quote from: bostonman on November 22, 2023, 03:51:24 amI am decidedly on "team commercial flux remover", rather than IPA. While IPA is cheaper, it's simply not as good as the blends of solvents used in commercial flux removers. That means you can get away with using far less of it, and it takes less time. To me that's well worth the $10-15 per can. Especially if done using the "mopping" method above, rather than flooding/submerging, since you need far less solvent.Another electronics technician in another department at work (whom I used to work with) swears by Safewash, so now that the aerosol cans aren't sold anymore, he's ordered a canister and is going to share some with me.Hopefully I can get an ultrasonic cleaner to use it in. I also have wondered if it's feasible to use it in one of the labware dishwashers in the chemistry labs. (That is another established, accepted PCB cleaning method.) I just don't know whether those labware dishwashers allow disabling the automatic detergent dispensing to let you manually use a different cleaner. I have also been considering switching to water-washable flux, but I need to do some testing to ensure it's safe in the long run. And of course I wouldn't use it for stranded wire at all, since there's no way to clean it.

author: bostonman
author_rank: Super Contributor
timestamp: December 01, 2023, 02:51:51 pm
content: QuoteI was thinking of a somewhat recent board I repaired (over the course of several months) for my Agilent oscilloscope. I found the solder for the components to be weak.In fact, I had to replace a ZIF connector on this board and the pins nearly pulled off the solder. The connector was in a tight location and I was shocked to find how easy it was to remove. I don't remember the degree of how easy the pins removed from the solder, but I began questioning the entire board at that point.Also, on a side note, this board had RF covers over the four channels. The covers easily came off, however, there were tiny metal clips that the RF cover (shield) went into. The acid brush kept getting stuck in these clips, and that caused lots of issues with trying to clean the board properly; especially since two chips required hot air and it had lots of flux in the area.QuoteGood to know. Unfortunately most of any work is repairing, so I end up with a mix of components and/or components that don't have a part number on them, however, obviously this is worth keeping in mind. I knew crystals would certainly be dangerous to put in ultrasonic.

author: uer166
author_rank: Super Contributor
timestamp: December 03, 2023, 09:20:19 pm
content: I've been washing PCBs in my dishwasher with Alconox with much greater success than using solvent here or there. They require a baking process afterwards, but come out absolutely clean.