Smitty Two writes:

Yeah, I disagree with many on that score. I still maintain that the
difference in ease and quality of soldering with and without the
addition of a drop of auxiliary flux is generally pretty astounding.

I've found it depends a lot on how clean the surfaces being soldered
are. Soldering relatively new components onto a circuit board that has
been pretinned, or is *freshly* cleaned bare copper, needs nothing more
than flux-cored solder most of the time.

On the other hand, equipment that's a couple of decades old has oxidized
surfaces everywhere, and a bunch of mechanical cleaning plus extra flux
is often needed to get a good joint. I have a bottle of rosin flux
dissolved in alcohol that I paint on as needed. You can also get flux
in little pens with felt tips that look like magic markers.

Dave