Cleaning PCB

IPv6Freely

Active member
I finally bought some 99% IPA and used a (new) toothbrush to clean a PCB. Now it's sticky for some reason and the solder joints are dull, like they've been oxidized (I assume that's just the sticky residue, whatever it is).

What have I done wrong, here?
 

peccary

Well-known member
You're basically pushing the flux around unless you either let the alcohol run off the board, or if you use something to absorb the alcohol before it dries.

Kimwipes make for a suitable solution...or paper towels. Just make sure you get the lint off afterwords.

Happy scrubbing!

@Stickman393 is right. I should have mentioned: when I scrub with a toothbrush I am actually scrubbing a Kimwipe that is covering the board.
 

jubal81

Well-known member
I've dumped the alcohol into a Tupperware container and brushed the PCB while it's submerged. I've got a friend who even uses and ultrasonic cleaner, like what they advertise for cleaning jewelry.
 

IPv6Freely

Active member
I've dumped the alcohol into a Tupperware container and brushed the PCB while it's submerged. I've got a friend who even uses and ultrasonic cleaner, like what they advertise for cleaning jewelry.
Can you really just dunk an assembled PCB into a tub of alcohol like that?
 

bowanderror

Active member
With 99% IPA, I usually have to douse the board (or apply with toothbrush) & let it sit for a minute before I start scrubbing with a toothbrush. Then dry it off and FULLY clean the toothbrush with IPA. Now you should have the easy stuff off, so you can re-soak the toothbrush and go at it again, focussing on the built-up areas of flux. Repeat until clean and place in front of a fan to dry. The surface of your joints may look dull, but it won't affect the connectivity. Note that if you need to resolder something after cleaning, you may have to add extra flux to do it.

Some fluxes don't come off easily, even with 99% IPA, so I have moved mostly over to a dedicated spray flux cleaner. I've had good results with MG Chemical 4140 Flux Remover, but other dedicated sprays should work. It only takes me 2-3 passes with minimal scrubbing to remove even the toughest fluxes.
 

IPv6Freely

Active member
With 99% IPA, I usually have to douse the board (or apply with toothbrush) & let it sit for a minute before I start scrubbing with a toothbrush. Then dry it off and FULLY clean the toothbrush with IPA. Now you should have the easy stuff off, so you can re-soak the toothbrush and go at it again, focussing on the built-up areas of flux. Repeat until clean and place in front of a fan to dry. The surface of your joints may look dull, but it won't affect the connectivity. Note that if you need to resolder something after cleaning, you may have to add extra flux to do it.

Some fluxes don't come off easily, even with 99% IPA, so I have moved mostly over to a dedicated spray flux cleaner. I've had good results with MG Chemical 4140 Flux Remover, but other dedicated sprays should work. It only takes me 2-3 passes with minimal scrubbing to remove even the toughest fluxes.
Thank you! I had wondered if there was something better out there. I'll check it out!
 

mistersparkle

New member
I may get flamed for this, but I use spray brake cleaner to de-flux my PCBs. And even though the stuff I use is advertised as containing <10% VOCs, I realize it's still horribly wrong environmentally. But, I guarantee I clean waaay fewer PCBs in a year than my local auto mechanic cleans brake parts, not to mention that Isopropyl Alcohol isn't an entirely innocent solvent either. So, like everything else, use these chemicals responsibly and in moderation. And I will check out that MG 4140 when my brake cleaner runs out.....promise!
 

bowanderror

Active member
I've heard of people using brake cleaner, with mixed results. They are usually acetone and/or methanol, with a bit of toluene in there. Acetone will melt some plastics, so it may not be the best option, but methanol should work fine (although it's toxic, so keep it off your skin & work in a ventilated area).

I have seen a few brake cleaners that use tetrachloroethylene, which is HELLA toxic, so I would steer clear of those.

Brake cleaners that use naptha or petroleum distillates should be ok, but you might want to test it on plastics first.
 

IPv6Freely

Active member
Is the 4140A the same stuff, for the most part? It's readily available on Amazon, whereas the 4140 doesn't seem to be. I'm sure for my needs it's plenty either way. I guess I don't really NEED to clean any of it, but damn it looks so good when you do!
 

Feral Feline

Well-known member
What about good ol' contact cleaner?
No, not the stuff for your corrective-vision lenses, but spray-can contact cleaner for electronics (I just picked up a can).

I've been using alcohol and a toothbrush, but not pleased with the results.
 

danfrank

Well-known member
I have seen a few brake cleaners that use tetrachloroethylene, which is HELLA toxic, so I would steer clear of those.
Yeah, the "brake cleaners I've seen use chlorinated solvents which will eat through a lot of things used in electronics. A big No No...

Go to the hardware store and buy a can of acetone. Mix it 50/50 with your 99% isopropyl alcohol, the mixture will work much better than your 99 iso only. In fact, many flux cleaners are exactly that... Iso + acetone. Most plastics used in electronic components (polyethylene and polypropylene) aren't affected by acetone. Acrylics are affected though, so watch out with other plastics. Mixing it up yourself will save you money!!! Lol.
I wouldn't dunk the assembled board in a Tupperware of solvent either. Just use a polyethylene squirt bottle to squeeze the solution out plus a toothbrush ti "brush" the solvent and flux off.
 
  • Like
Reactions: fig

quality_jones

Well-known member
What about good ol' contact cleaner?
No, not the stuff for your corrective-vision lenses, but spray-can contact cleaner for electronics (I just picked up a can).

I've been using alcohol and a toothbrush, but not pleased with the results.
Yeah, once someone buys another pedal from me, a can of the WD-40 contact cleaner is at the top of my list. Well, that and it's time to re-do my potentiometer inventory.
 
Top