I'm resurrecting an old thread that I originally started.
Recently I repaired a vintage Commodore mouse with plastic mechanical parts. Due to the plastic and age, I was reluctant to use anything but Isopropyl alcohol. As usual, I grabbed a brush (tooth brush this time), dipped it in the Isopropyl alcohol, and scrubbed all the flux. After drying, not only was the section I brushed white with flux residue, but spread to other areas.
I repeated the wash and got it cleaner, however, some was still sticky. The only thing that seemed to work was using a can of air to wash off the alcohol and dry it quicker.
If I remember correctly, back at my old job I'd leave a PCB submerged in alcohol, scrub it clean, and would still see white residue after it dried.
My assumption would be the Isopropyl alcohol is strong enough that it deludes the flux, scrubbing it clears it away, more fresh alcohol, eats the remaining, and then another dose of alcohol, and it dries clean.
This doesn't seem to be the case. My confusion is what am I doing wrong, and, also, I'd like to put a few bottles of Isopropyl alcohol in a metal pan to wash boards in the future but sometimes the alcohol mixes with the metal and causes the alcohol to become mixed with metal tarnish residue.
Does anyone have recommendations for a pan and ways to stop my boards from remaining white/sticky?
First of all, it's important to distinguish between sticky residue and white residue, because they're very different things. (They can occur alongside each other but are not the same thing.)
Sticky residue is, plain and simply, leftover flux. Thin layers of it dry glossy.
White residue is the result of chemical reactions in the flux during soldering, producing ionic contaminants that are not solvent-soluble. (This is oversimplified, the Chemtronics document linked above goes into more detail.)
Sticky or glossy residue is removed by simply cleaning longer. If you're submerging the boards, let them dwell longer. I sometimes just wet the board in solvent, and place it into a ziploc bag together with a paper towel soaked in the same solvent. This prevents the solvent from just drying off right away.
White residues won't go away anywhere near as easily, because the entire problem is that they aren't soluble in the solvent being used.
Regardless, what seems missing from all of your cleaning regimens is actually
removing the residue-laden solvent. It sounds like you think solvents destroy the residues, but all they do is mobilize them. If you use solvent to dissolve the residues, but just brush them around the board, they're not actually gone, they'll just be spread out once dry. Similarly (and reiterated in your paintbrush story) soaking in solvent simply dilutes the residues, but whatever solvent is left on the board (or brush) still contains residues. You have to remove the residue-laden solvent if you want to remove the residues. Otherwise you're just moving them around and redepositing them elsewhere.
(This reminds me of people who mop their floors in a single pass, without going back with clean water and a well-squeezed mop afterwards. Sure, the mop has picked up some of the dirt into the bucket, but you're also leaving behind a film of dirty water everywhere. Unless you actually lift that dirty water away, you're depositing dirt and soap everywhere.)
I have mostly moved away from cleaning PCBs by drenching with copious amounts of solvent. Instead, I use a brush dipped in solvent to scrub an area of the board, then use this brush (the "dirty" brush) to mop up the residue with a kimwipe (or other lint-free wipe). Stubborn areas may require this step to be repeated. Do this for the entire board until there is very little residue. If you have an air compressor, blow out underneath chips, too.
Then take a fresh wipe, lay it onto the board, and take a second brush (your "clean" one) dipped in clean solvent to mop it clean. In essence, think of how you use Windex and paper towels to polish a window. The "clean" brush's purpose is really just to let you manipulate the wipe, since our fingers are much too fat to be of use.
If, after all this, your board exhibits sticky or glossy residue, then your cleaning was simply incomplete and needs to be redone. But if it exhibits white residue (and no sticky/glossy residue) after drying for a few hours, then you need to find a different solvent.