One could use solder with the more modern "no-wash" fluxes, and use a
flux pen for additional purposes, like fluxing the IC leads and pads first.
If one does that, use isopropyl alcohol ~75% (balance is water) for
wash as follows:
1) Soak for 0.5 hr, rinse and soak again, then final rinse. Air or oven dry.
2) Rinse and use artist short-hair brush to remove flux; repeat at least
3 times, then two final rinses. Air or oven dry.
WARNING! WARNING! DANGER! DANGER!
I have learned the hard way: never use a "no-wash" flux and then expose
the PCB to any kind of solvent. "no-wash" fluxes contain basically a
plastic that is supposed to trap the ionic stuf that is in the flux. If
you expose the board to a solvent, the plastic stuff partly loses its grip
on the ions and they head straight for the most sensitive circuit on the
PCB. The remaining plasic stuff then serves to hold the ions exactly
where they cause the most trouble.
The company that I use to do coating and potting strongly recomends that
easily washed fluxes be used. Next on their list is the stuff that takes
fair amounts of non-polar solvent. For the "no-wash" stuff they suggest
you send it somewhere else to be cleaned.
That being said, i have yet to find a relatively safe solvent for
rosin; isopropyl soak method removes most, but not all of it.
There is evil smelling stuff called "ensolve" that works but you can't buy
it in the hardware store.
Some people claim to have luck with switching back and forth between
mineral spirits and water based cleaners. The mineral spirits lifts the
non-polar stuff to let the water at the ionic stuff. The water gets the
ionic stuff away so the mineral spirits can get to the next bit of
non-polar.
