Hi Mike,

That is the new (10 years old - new) almost environmentally correct
solder flux. It is citrus based (IIRC) and is meant to be washed off
the board with hot water and detergent. Do that and it is the simplest
stuff to use.

I don't use it, though, because its fumes stink so bad that I am sure
they must be bad for me. So I continue to use rosin core solder, and
then use isopropyl alcohol to remove the flux.

You shouldn't leave flux on any solder joint. If you are steadfastly
determined to do so anyway, there are several fluxes available in the
Kester solder line that leave a very minimal amount of residue.

-Chuck Harris

Mike Knudsen wrote:
I just received the following from a friend who has been building electronic
circuits for his home pipe organ (talk about boat anchors). He got shorts in a
solid state circuit, so imagine what the new solder he describes would do in
high-impedance tube gear!

Apparently some solder makers are using a new "organic" flux that cleans off PC
boards easier, but is conductive. I quote:

At the point that I had completed 5 of these, I ran out of my usual spool of
Kester solder and began using another (spool of Kester solder). I recall that
the odor of the melting flux was strange and different than that of the older
spool.

Now I discover that the flux residue on the new spool is CONDUCTIVE! It's easy
to discern the difference between the old and the new: the earlier "rosin"
material was yellowish and hard, and when you picked at the edges of it, it
would break off in hard granules. The new residue is clear and soft, about the
consistency of ear wax. (The label on the spool says that the flux is
"Organic," so perhaps it *is* ear wax.)
(end quote)
--Mike K.

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