IPA gets sticky?! - Page 1
Forum section: electronics / beginners

author: ppeterl
author_rank: Contributor
timestamp: June 28, 2019, 09:37:31 pm
content: So I soldered thishttps://www.muffsy.comkit together, and then I cleaned off the solder flux residue with IPA as usual. This time, however, the solder mask, or coating or whatever on the board got all sticky; it lost its glossy finish for a matte one and also got my fingerprints on it. I've noticed the same thing on some vintage circuit boards before as well.I searched this forum of course for an explanation but got no good hits. What is the recommended way to remove flux on this kind of boards?

author: cur8xgo
author_rank: Regular Contributor
timestamp: June 28, 2019, 09:42:06 pm
content: Quote from: ppeterl on June 28, 2019, 09:37:31 pmYou didnt clean it properly. Use more IPA, rinse well, use high percentage IPA, etc..etc..

author: floobydust
author_rank: Super Contributor
timestamp: June 29, 2019, 05:31:58 am
content: I have the same problem with some chinese made PC boards. IPA seems to attack the solder mask, it loses its shine and goes sticky and dull.OSH Park boards do this, very annoying. I think the solder mask is cheap and not compatible with IPA, even diluted with water.The solder mask seems to be only for water soluble flux.

author: tooki
author_rank: Super Contributor
timestamp: June 29, 2019, 10:52:18 am
content: My guess is that it’s also more likely to be flux residue than the solder mask itself softening. If you keep cleaning it, does it eventually get even softer, or does it reach a point where it dries glossy again, especially if you polish it dry with fresh IPA?

author: Paul Rose
author_rank: Regular Contributor
timestamp: June 29, 2019, 03:51:12 pm
content: Agree with cur8xgo and tooki.You are still dealing with flux, not softened solder mask.Soft stick residue with fingerprints, etc. is the flux partially dissolved and spread all over the board.More IPA, stronger IPA, use a brush. It will eventually come clean.

author: Paul Rose
author_rank: Regular Contributor
timestamp: June 29, 2019, 03:59:13 pm
content: I use just 91% because it is easy to get locally.I pour it into a flat bottomed container deep enough to get to the solder when I put the board flat into the container.I let is sit for a while, then use a toothbrush ( not your wife's) and scrub. I repeat this a few times.I use a second batch of IPA for final "rinse". Which is just repeating the process once more with fresher IPA.If I'm doing several boards, I use a second container for the "rinse".It takes some work, but the boards always come clean.

author: wraper
author_rank: Unknown
timestamp: June 29, 2019, 04:04:20 pm
content: Many people for some reason think that once you sprinkle PCB with IPA and brush it, flux will miraculously disappear into nowhere. While in reality it's just spreading flux over the board. To get flux off the board, you either need a lot of IPA to wash it away or use wipes which will absorb flux dissolved in IPA. Several cleaning passes are needed in any case.

author: ebastler
author_rank: Super Contributor
timestamp: June 29, 2019, 04:22:09 pm
content: Quote from: Paul Rose on June 29, 2019, 03:51:12 pmI agree that you are dealing with flux residue. But I don't agree with the "stronger IPA, use a brush". If the flux gets spread all over the board, as it has in your case, it has obviously been dissolved just nicely.What's missing is to remove the solvent/flux mixture from the board, rather than letting it evaporate and dry again. As wraper said, wipe it off, rinse, and repeat.

author: cur8xgo
author_rank: Regular Contributor
timestamp: June 29, 2019, 04:43:49 pm
content: I concur with the other responses here. I dont use IPA for flux cleaning unless I am working on such a small board that I can put alot of IPA on it and let it drip off with gravity. Just too much hassle to make an IPA bathtub for me anyway, although that is how I have seen professional assemblers clean boards and they come out spotless.You could always use something more aggressive. The electrical contact cleaner from the auto parts store is pressurized and really does a job. Good for small spot cleans near an edge.

author: Nerull
author_rank: Frequent Contributor
timestamp: June 29, 2019, 07:06:50 pm
content: Quote from: wraper on June 29, 2019, 04:04:20 pmIndeed, IPA is a *solvent*. It doesn't destroy flux, it dissolves it. And redeposits it when it dries. You have to get it off the board before this happens.

author: JFJ
author_rank: Regular Contributor
timestamp: June 29, 2019, 09:42:08 pm
content: There's an old, but useful, article about PCB rework, repair and cleaning in the July-October 1982 issue of Hewlett-Packard's Bench Briefs:http://hparchive.com/Bench_Briefs/HP-Bench-Briefs-1982-07-10.pdfThe case for not removing flux is argued on page 9. While advice on how to remove flux (when you must) begins on page 10.

author: GreyWoolfe
author_rank: Unknown
timestamp: June 29, 2019, 10:26:06 pm
content: Wet Kim-wipes with 91% or higher IPA and scrub with toothbrush. Repeat until flux is gone. No stickies or white residue.

author: cur8xgo
author_rank: Regular Contributor
timestamp: June 29, 2019, 11:15:57 pm
content: Quote from: GreyWoolfe on June 29, 2019, 10:26:06 pmYa I've seen pros do exactly this as well

author: Psi
author_rank: Super Contributor
timestamp: June 29, 2019, 11:49:01 pm
content: Yep, pretty much what others have said.iso does clean flux of PCBs quite well but you have to keep few things in mind.- Needs to be pure iso, ~97+%- When the iso evaporates off your board the flux dissolved in that iso will return its flux to the board. So don't let it evaporate! To dry the board hit it with compressed air to blow off this iso before it evaporates. (Note: iso fumes are flammable!)- iso cannot hold a lot of flux dissolved in it, it gets saturated very quickly. If your tray of PCB cleaning iso already contains lots of flux in it you will never be able to clean your board very well because you are always putting 'dirty' iso back onto the board.- You need to scrub the boards to get the hard flux deposits.To clean a PCB properly using iso you need two separate iso wash baths/trays and an air compressorA) For the 1st bath use a brush and scrub the board down with iso, Try to keep the iso flowing over the board as you scrub.This stage gets into the cracks and dissolve the hard depositions of flux into solution. (If you don't scrub all the hard flux off the board in this step then your board will not come out nice and clean at the end)B) Remove the board from the wash and give it a spray with the air compressor to remove all the iso on the board.(This step is optional you can just move straight to the 2nd bath but you will contaminate your good iso bath with dirty iso much faster if you do.C) Now move to the 2nd bath, this one needs to be in good clean iso otherwise it wont work so well.Put the pcb into the iso and give it a good shake, let the clean iso flow over the board. You are trying to clean off the flux residue that is just sitting on the pcb surface so you don't need to scrub it. This stage gets rid of the white streaking and stickiness. You can use a very mild brush if you want but don't hard scrub it or you will release flux you may have missed in step 1 and this will make your job harder.D) Remove the PCB and dry it with the air compressor again.(I use 100psi and the iso leaps off the pcb drying it instantlybut again, iso fumes are flammable and air compressors have motor which can make sparks, so don't do this next to the air compressor !You will find this process works really well initially but you will have to keep replacing the 2nd iso bath with new stuff after a few boards.The 1st iso bath can get quite dirty and still work ok, so, to save on iso, when the 2nd bath gets too dirty make that become the 1st bath and pour a new clean 2nd bath.This is one reason why iso is not very good at PCB washing, it works well but is very quickly saturated with flux and you need new stuff.It's quite wasteful.You can get much better liquids to clean flux before they need to be replaced but they are quite expensive.

author: floobydust
author_rank: Super Contributor
timestamp: June 30, 2019, 12:29:11 am
content: Note- soldermask contact time for pure IPA is 2 minutes, and up to 15 minutes for 75% IPA. Don't soak a board in it for a long time.IPA is a solvent that attacks solder mask, that has nothing to do with flux.

author: GreyWoolfe
author_rank: Unknown
timestamp: July 01, 2019, 01:13:00 am
content: Quote from: cur8xgo on June 29, 2019, 11:15:57 pmJust standing on the shoulders of giants.

author: BravoV
author_rank: Super Contributor
timestamp: July 01, 2019, 03:42:13 am
content: My favorite IPA container, with small & sharp tip and controlled spraying, stolen from wifey's spare blank ketchup container.Works all the time as I can flush a particular tight spot with small brush action, until all the flux residues gone, no hazy film left, leaving a clean & shiny board surface. :-Random image from Google.