Removing flux from a PCB... by placing the PCB into a pot of boiling water? - Page 1
Forum section: electronics / beginners

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: October 14, 2025, 01:06:36 am
content: Call me crazy but I'm considering throwing a PCB covered in flux into a pot with boiling water (dedicating the pot to just PCB cleaning), letting the PCB stay in the boiling water for a few minutes, tossing out the water, and then repeating the process again.Anyone tried this before?I know that I can't use this tactic on ultra-sensitive components (certain exposed sensors, diaphragms), but it should be mostly fine, right?I have an ultrasonic cleaner, various PCB cleaning brushes, used rubbing alcohol, ethanolamine, and various other tactics to try to remove flux, but boiling hot water has always seemed to work best for me.

author: Psi
author_rank: Super Contributor
timestamp: October 14, 2025, 01:32:40 am
content: I assume you are using water soluble flux?The main thing to be concerned about is getting all the water off the PCB while its still liquid, some of it will get trapped under ICs and leave behind salts/solids if you let it evaporate instead of removing it while it's still water.If using water I would use deionized water, not tap water, but the water wont stay deionized so I'm not sure how long it will last for multiple uses.

author: free_electron
author_rank: Super Contributor
timestamp: October 14, 2025, 02:14:45 am
content: works for water soluble flux. use distilled and deionized water , unless you want hard water spots everywhere

author: CaptainBucko
author_rank: Regular Contributor
timestamp: October 14, 2025, 02:27:41 am
content: I use PCB Cleaner designed for the job, about 150mls in a zip lock bag with the PCB. You lower that (with bag open) to remove air into your ultrasonic cleaner full of water, then seal it up when the air is expelled. 30 mins at 50 C, remove from bag, wash under hot fresh water (or distilled if you live in a hard water area) and dry at 50 c for 30 mins. I'm in a soft water area so I see no dried residue. I'm still using the same PCB cleaner for PCB #10 and I don't see any decrease in cleaning action.Your idea makes sense for water soluble flux, heat and ultrasonic will help. The PCB cleaner will do a better overall job, including oils and other contaminants. Since moving to the zip lock bag method, I waste so little cleaning chemical, it worth spending the extra to buy and use it as per above.

author: ejeffrey
author_rank: Super Contributor
timestamp: October 14, 2025, 02:56:43 am
content: A PCB safe detergent and agitation will definitely help a lot. I would expect that a simple hot water soak, even with boiling hot water to leave a lot of stuff behind.And yeah, rinse with RO/DI water to avoid leaving minerals behind while drying. Also try to blow as much of the rinse water away before it evaporates.

author: gamalot
author_rank: Super Contributor
timestamp: October 14, 2025, 08:00:56 am
content: Quote from: CaptainBucko on October 14, 2025, 02:27:41 amI clean PCBs pretty much the same way, but isopropyl alcohol instead of PCB cleaner.

author: jaykup
author_rank: Newbie
timestamp: October 14, 2025, 07:42:32 pm
content: Quote from: CaptainBucko on October 14, 2025, 02:27:41 amIs there any risk in cleaning PCBs with electrolytic or polymer capacitors on it using this method? I've always cleaned boards without them in the ultrasonic cleaner because I was worried about damaging the caps somehow, but I was never certain.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: October 17, 2025 01:28:54 pm
content: I would thoroughly blow off the water with compressed air, after rinsing for the final time. I have a large compressor that has a 30 gallon tank, at up to 150 PSI, (10.55 kg/cm²), so compressed air is not a problem for me. If plentiful compressed air is not available, you can used the canned compressed air,but you won't get the volume, or high enough pressure, but it's better than nothing. Also, a hair drierwould help by adding heat that won't harm anything. That's all I had to add.

author: Psi
author_rank: Super Contributor
timestamp: «Reply #8 on:Todayat 12:35:09 pm »
content: You can also buy those small handheld ducted fan blowers, like the wolfbox, if you want high speed air to replace canned air dusters and dont want to have a huge air compressor.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: «Reply #9 on:Todayat 01:09:50 pm »
content: Quote from: Psi onTodayat 12:35:09 pmOh Yeah, Psi, I forgot about those, they are handy. I have one, but use it in the vacuum mode, to clean crumbs off my keyboards, (no idea how they get there.