Electronics > Beginners
isopropanol question
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David Hess:
Isopropanol has the virtues of being inexpensive and readily available and safe but by itself is not a very good flux solvent.
ebastler:
But even the best solvent does not make the flux evaporate or otherwise dematerialize. The actual problem which the OP has encountered will remain the same: You have to get that solvent/flux mixture off the board, by wiping it off and/or rinsing.
bob91343:
I keep going back to 1,1,1 trichlorethylene.  That stuff dissolves everything you want to dissolve and doesn't seem to harm anything nor leave residue.

Unfortunately it's classified as hazardous and is thus hard to obtain.  I am lucky enough to have stockpiled a lifetime supply for myself.

Anyway it's better than anything else I have encountered.  I use a toothbrush on boards.  I drip it through pots and switches.  It does the job.

Like any other chemical, always test it on a tiny corner somewhere just in case the stuff could cause problems.
IanB:
Let's try an analogy. If you were to wet your hands then apply soap and rub to clean the dirt off, but then simply stopped and let your hands dry without rinsing, what would happen? You would end up with dirty, sticky hands. What do you actually do? You rinse your hands under clean running water before drying them.

To successfully complete a cleaning process, you have to rinse thoroughly after cleaning to wash the dirt away.

Same with cleaning a circuit board. You can apply solvent and rub with a soft brush to loosen the flux and dissolve it in the solvent, but the next step is you have to remove the flux that you have cleaned off. To do that, you have to rinse the board thoroughly in clean solvent to wash away the residue.

If you get an ugly white film on the board it means you haven't washed away the flux, you have simply moved it around a bit and let it dry on the board.
ejeffrey:
I'm not sure the propanol is actually dissolving the flux at all.  That looks like it softened the flux which then got spread around by the polishing cloth.

Either way, a pretty standard procedure is to use an appropriate flux cleaner, using plenty of it and some scrubbing to get all the flux off the board.  Then without letting it dry, rinse with DI water and blow off with filtered compressed air.  That will avoid the solvent from drying and redepositing the flux residue back on the board.

Organic solvents like isopropanol are often pretty dirty straight from the bottle.  Pour some "clean" iso on a clean piece of glass and let it dry to see.  That is why you want to rinse with DI water.  Even the DI water will have some dissolved contaminants but it doesn't dry as fast as alcohol so it is easier to blow it off.

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