Why Should We Clean Boards From Flux?

I’ve wondered the same thing. From what I was able to find in discussions here, it sounds like rosin flux residue from rosin core solder is probably not terminally corrosive and is mostly an aesthetic concern. If you’re adding additional flux (like maybe for smd stuff?) that might be different depending on what you’re using.

All that said, I did buy some mg chemicals flux remover liquid (not the heavy duty one) and some fancy esd safe brushes, and I cleaned my first board the other day. It looks nice at least!
 
I think flux residue can oxidize with time, turn into some brownish rusty aeras on the pcb, maybe able to create shorts, and damage the pcb traces.

The oxidization process can be a critical issue after decades or only a few years, depending on how much care we give to the circuit, like where is it stored, etc.

Might also vary according to the flux brands and qualities.

I'd say that cleaning is the kind of details that will help maintaining the pcb in good shape, and increase the circuit's lifetime.

Never did it, though it's certainly something that I should consider for all my builds someday.

I don't use flux, but I suspect there is always a bit of flux on most pcb, as finish treatment for a smoother soldering process ?
 
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I think flux residue can oxidize with time, turn into some brownish rusty aeras on the pcb, maybe able to create shorts, and damage the pcb traces.

The oxidization process can be a critical issue after decades or only a few years, depending on how much care we give to the circuit, like where is it stored, etc.

Might also vary according to the flux brands and qualities.

I'd say that cleaning is the kind of details that will help maintaining the pcb in good shape, and increase the circuit's lifetime.

Never did it, though it's certainly something that I should consider for all my builds someday.

I don't use flux, but I suspect there is always a bit of flux on most pcb, as finish treatment for a smoother soldering process ?
There is a flux core in most solder
 
You can always go with no clean flux! Hurry, one left at this price.... I got two pounds, works.
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Check your solder's datasheet. Some are no-clean and cleaning is either optional or impossible based on the type and others require cleaning like Kester 331, which should be rinsed within 48 hours.
This is really interesting!
Here is an excerpt from the solder I use "44" flux datasheet.

For Kester 63/37 24-6337-0027
 

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IMO: Cleaning flux off a board is merely a neatness thing. The only real problem with flux on the board is that it can accumulate dirt, dust & other detritus to a point where it can become corrosive or shorting things where it shouldn't. But that usually only happens on circuit exposed to the air. In an enclosure, there is low risk of such accumulation. Flux, by itself is not corrosive or conductive. It depends entirely on the datasheet for the flux so involved.
 
This is really interesting!
Here is an excerpt from the solder I use "44" flux datasheet.

For Kester 63/37 24-6337-0027
I'm not sure I use that exact solder, but I use Kester no-clean, and I never had much luck with IPA (which seems to be most people's goto), and maybe this is why. I usually use some version of WD40 contact cleaner (nothing like normal WD40) with a toothbrush and paper towel and it works great.
 
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