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| I just got in a pound of 63/37 kester .025" solder |
Which type? 331 is conductive. As for the others, I'd only risk leaving type 245 flux on the board, as it's the no-clean type. The others
can usually be left on the board, but sometimes this causes problems. If you carbonize the flux, it will be conductive. If you trap dirt in the flux, it can be conductive.
Even subtler, the flux changes the dielectric constant between two solder points, thus changing the parasitic capacitance. I've had boards where this problem caused oscillation, which went away when I cleaned the board.
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| soaking the stuff you build in 99% isopropyl for about a half hour, then dab in between traces/components with a paintbrush (removing any remaining residue) and dry the board using a fan or something. I've heard this procedure recommended to clean off the flux & other surface contaminants. |
If you're using professional PCBs and you fill most or all of the holes, you don't need the soaking. Instead, pour a bit of the alcohol into a small dish, dip a stiff-bristled brush into it and scrub the solder side of the board, while trying to prevent the sullied alcohol from getting on the component side of the board. Then use compressed air to blow the sullied alcohol off the board. Repeat until done. I use a stiff-bristled toothbrush for this, but if you're paranoid about static you should use a hogs-hair brush, which you can get from electronics supply places. Mouser has them, in the part of the catalog where the solder and such are.
With perfboard and PCBs with lots of unfilled holes, you usually end up contaminating the component side of the board: sullied alcohol gets through the holes, evaporates and leaves behind a thin layer of flux. Then what you need to do is drench the board and either scrub at it or soak it so most of the alcohol stays liquid while you blow it off. If there isn't enough alcohol, it evaporates instead of rolling off the board, leaving behind the flux. Even when you drench or soak the board, you'll need to repeat the cleaning except on the smallest boards.
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| acetone will clean the flux residues |
Yes, and it will also eat some plastics. Acetone is a heavy hammer best left unwielded most of the time.
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Flux isn't a residue, it's "supposed" to be there. The unwanted white stuff left behind when you use impure alcohol is a residue.
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I tend to doubt that. Most of that 9% will be water, but a fraction of that fraction will be impurities. With 99% alcohol (which is usually 99.x% in fact, where x > 0) the fraction of a fraction is truly too small to worry about.
