Many instruction booklets for domestic electronic equipment say do
not use cleaning solvents such as alcohol.
Is this advice given simply because they are trying to prevent
possible marking of the plastic casing?
Or can domestic cleaning solvents actually damage the electronics
inside in some way?
Alcohol isn't a solvent as it relates to the components on a Circuit
Card Assembly (CCA), per se (it will solve fluxes). They are talking
about reactive solvents like lacquer thinner, or benzene, or toluene,
or other petroleum based solvents. Any of those in the family that
would melt plastic parts. Another thing a solvent can and does do is
get into the vents of an EL cap and screw them up. One has to watch
for that as well.
If you have a bare CCA in your hands (mind proper ESD procedures)
you can heat up some alcohol (90% or better) in a microwave and wash
the board down, Or immerse it, then blow it off with air and you
should see no residuals. You should also bake it out at 60C for a
bit.
Most modern assembly facilities these days use "water soluble"
fluxes, and if you have a good oven that has good temp control, you
can wash a CCA with water (not if it has transformers on it) and then
bake it out for an hour at 60C to dry the CCA and the PCB itself out.
The alcohol is what I use as it "dries" a lot easier, and requires
much less baking time (15-30min). The reason I use it hot is so it
doesn't attract water so much. Hot air gun even works if you are
careful with it.
I wouldn't use any cleaners on an assemble product that has plastic
housings, or places that can trap liquids.
I disassemble if I want PCB assembly level cleaning.