I recently read someone here mention that they used mineral spirits
(MS) to remove flux. Since I had some around I gave it a go. It
seemed to work about as fast as 91% IPA, but left less flux residue
spread around the board (i.e. none). I found a manufacturer's
reference to using mineral spirits in place of chlorinated hydrocarbon
solvents to remove non-corrosive solder flux from copper here:
http://www.fusion-inc.com/filler2.htm#anchor237100although, since it's paste solder they're talking about, I suspect
they're taking about using MS to remove flux from copper pipe joints.
I also found another site:
http://www.logwell.com/tech/servtips/cleaning.htmlwhich discussed a few of the substances they used in the cleaning of
electronics in general:
"Our work bench is also stocked with a MENDA dispenser full of
denatured alcohol. Denatured alcohol is ethanol with small amounts of
methanol or other denaturing agents added to render it unfit to drink.
... Denatured alcohol is very good for cleaning soldering flux; it is
now our favored circuit board cleaning agent since the demise of 1,1,1
(1,1,1 Trichloroethane a/k/a methyl chloroform)... Rubbing or
Isopropyl alcohol is a considerably less efficient cleaner and it
makes your shop smell like a doctor's office. Commonly available
"rubbing alcohol" is usually 70% isopropyl alcohol with the balance as
water. Anhydrous or 100% isopropyl alcohol is available and is
sometimes used as an industrial flux cleaner. Occasionally, a
stubborn stain will yield to one of the alcohols when all other
cleaning agents fail, but ordinarily they are mediocre performers.
Both denatured ethanol and isopropyl alcohol are generally safe on
plastics, but ethanol will mildly attack a few plastics."
About denaturing agents used in denatured alcohol:
"The completely denatured alcohol formulation used in the United
Kingdom contains (by volume) 89.66% ethanol, 9.46% methanol, 0.50%
pyridine, 0.38% naphtha, and is dyed purple with methyl violet."
Other "typical additives are methanol, isopropanol, methyl ethyl
ketone, methyl isobutyl ketone, denatonium benzoate, and even aviation
gasoline."