Anyone cleaning the flux off using an ultrasonic cleaner?


  • Hero Member

    I saw a youtube video where the guy was cleaning the flux off his boards using an inexpensive ultrasonic cleaner and denatured alcohol. Seemed to work for him. Amazon price for an ultrasonic cleaner is around $30.

    I've seen others where they just use water in their ultrasonic cleaner and then rinse off with something else to displace the water.

    Heating the solution to 50 or 60C is alleged to help, but apparently cleaning at room temperature will also work. Not sure. Anyone here doing it have an opinion?



  • @NeverDie I just use isopropyl alcohol and a paint brush! Cheap and effective.



  • I own a regular household ultrasonic cleaner. 50W, 46 kHz, without manual heating control. I've tried cleaning a PCB once with distilled water, but it wasn't very promising. Not all of the flux came off and the board was still sticky after blowing it dry with compressed air. Then again, I'm using rather tacky homemade flux made of rosin, isopropyl and a bit of glycerin.

    Anyway, I wouldn't want to use large amounts of alcohol or similar volatile solvents in a semi-open device, that also heats up when in use. That just sounds like a fire hazard waiting to happen, since it evaporates rather quickly and the flash point is below room temperature (e.g. isopropyl is somewhere between 10 - 15°C). With enough vapours in the air, a spark (static discharge?) near the cleaner might be sufficient for a neat little explosion, in a worst case scenario. Industrial ultrasonic cleaners might have some kind of safety features to reduce the risk of explosions and / or fires, I guess. I'd rather try a less dangerous, commercial ultrasonic cleaning solution for electronics, but I have no suggestions for that.

    Since I'm not dealing with large amounts of PCBs that need to be cleaned, I stick with isopropyl and a tooth brush, like skywatch.


  • Hero Member

    @BearWithBeard said in Anyone cleaning the flux off using an ultrasonic cleaner?:

    isopropyl and a tooth brush,

    Exactly what I've been using to date, and then blowing it dry with compressed air afterward. It works, but for some reason I hate doing it, so I was looking into whether there's some easier way.



  • I get what you mean. It's dumb labour, messy, splatters everywhere.

    I guess, since isopropyl alcohol is a good flux solvent on its own, pouring some in a small sealable container, in which you can then barely submerge a PCB for a few minutes, should work aswell. Maybe even agitating it a little bit. Similar to how people etch PCBs in ferric chloride.


  • Hero Member

    @BearWithBeard Many if not most of the ultrasonic cleaners have lids on them, so that puts a limit to how much solvent evaporates (due to vapor pressure). Thinking about it now, I'd wadger the explosive potential is quite limited. For sure you'd want a lid that doesn't lock tightly closed, so if it were to blow-up, it would just blow the lid off/open, not create shrapnel. I suppose a hinged lid would be best so it doesn't go flying. For that reason, I think the risk is probably low.

    Denatured alcohol is cheaper than iso, so presumably it wouldn't cost much to submerge a pcb in it. I can't say that I've tried it though. Any reason it wouldn't work just as well as iso?



  • @BearWithBeard I do the 2 container method for cleaning pcbs with isopropyl. First container is the "dirty" one which gets the pcbs first and they soak for a couple minutes. Then each pcb gets the electric toothbrush treatment above the dirty container and then they go for a rinse in the "clean" container. Once the clean container starts to soil it becomes the dirty container and the old dirty container is cleaned and fresh isopropyl is added. Just like washing dishes. I actually worked for a place that used a standard dishwasher to clean (large) pcbs. It worked surprisingly well.


  • Hero Member

    I guess there's something wrong with denatured alcohol. Otherwise, I'm sure everyone would be using it instead.

    Buying 99% ISA in 12 bottle quantities from amazon would save over the one at a time approach, so maybe I'll go that route.



  • @NeverDie Well, I have safety concerns because of the relatively large amounts of liquid that are needed. IIRC, my ultrasonic cleaner requires to be at least half-full, which is a little more than 250ml, or one bottle of isopropanol. And after the 5 minute bath, what do you do with it? Dumping it seems wasteful, transfering it back into a bottle is inconvenient and again, potentially dangerous, depending on the environment. Leaving it in the cleaner for the next use? Nah, I'm not risking it. It might be fine 99% of the time you use it, but you also wouldn't make a narrow cut on a table saw without a push stick, would you?

    What I think could be a good compromise, is filling the ultrasonic cleaner with water and place the PCB in a zip bag filled with enough solvent to submerge it, squeezing the air out and then place that bag in the cleaner. Like sous-vide cooking. It provides isolation and the solvent, of which is much less required, can be handled separately in a save location.

    Oh, and regarding isopropanol vs ethanol: Here in Germany, I can get a liter of 99% isopropanol for about 3 EUR. That's not really much more than 96% denatured ethanol. With ethanol however, I found that it tends to leave some sort of film on the PCB, which has a kind of dull and blochy appearance. Not the uniform, shiny finish you would like to see after cleaning. Also, while making my own flux, I found that pure rosin dissolved better in isopropanol than in ethanol. And while some of the rosin in ethanol started to crystallize after a few weeks, the isopropanol-based flux is still completely liquid after over a year.



  • to reduce evaporation i saw a guy doing the following method. he fills the container with regular water up to middle mark and then gets some fridge ziplock bags fills them with cleaning solution or just IPA puts the pcbs in the bag locks them and tosses bag into the water filled ultrasonic cleaner. when it finished just takes out the pcbs and locks the bags again for later use until the solution or alcohol is not usable. sounds very practical but i dont have experience with it.



  • @NeverDie Here in Canada we can buy 99% ISA from our local pharmacy for a couple bucks a bottle so that's why I normally go that route. Question, have you tried the actually flux cleaner like this before?


  • Hero Member

    @Jon-Raymond No, I haven't tried that one. Looks pretty toxic, though I imagine it works a treat. Is that what you use? I've only used IPA with a toothbrush. I started off using 99% IPA from aerosol cans but later migrated to the pharmacy stuff because of cost.

    Here pharmacies sell 91% and 70% IPA because they have more disinfection power than the 99% (due to longer dwell time).



  • @NeverDie Before when I used SN63/PB37 Rosin Core I needed to mix a solution of IPA and Acetone to clean the flux residue off. IPA alone wouldn't do it. I have since switched to using SN63/PB37 "No Clean" solder for all through hole parts and have found using only IPA does a good job of cleaning.

    You're right about the toxicity of the commercial (and home made products). Whenever possible I do all my board cleaning under a fume hood that I also use when reflowing boards. It's a simple enclosure with an exhaust fan that vents outside.


  • Hero Member

    @Jon-Raymond Acetone has a tendency to dissolve many plastics, so I'm not sure how compatible it is with IC packaging and such. Unless maybe they're made from polypropylene? I just don't know.

    I've read that brake cleaner (the kind containing Tetrachloroethylene ) can be quite effective as a flux remover. It's also cheap, which is why some people use it. However, without a hood such as you have, it can be quite bad for you biologically. That's why I thought perhaps using an ultrasonic cleaner with less toxic (but comparatively less effective) flux cleaners is better for my environment.



  • @NeverDie IC encapsulation is almost always a thermoset polymer as they need to withstand the reflow process. The added benefit of this is that they are not dissoluble by acetone. I wish they were as it would make de-encapsulating IC so much easier. I generally have to use an acid to de-encapsulate. I haven't tried brake clean but would think it would work well.


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