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IPA gets sticky?!

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JFJ:
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.pdf

The case for not removing flux is argued on page 9. While advice on how to remove flux (when you must) begins on page 10.

GreyWoolfe:
Wet Kim-wipes with 91% or higher IPA and scrub with toothbrush.  Repeat until flux is gone.  No stickies or white residue.

cur8xgo:

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

--- End quote ---

Ya I've seen pros do exactly this as well

Psi:
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 compressor

A) 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 instantly :)  but 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.

floobydust:
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.

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