What is the use of FLUX when we solder?

To remove oxides / sulphides etc from the surfaces being soldered.

Graham

It combines with the surface oxide and excludes atmospheric oxygen from making more oxide.

This allows the liquid metal (solder) to contact solid metal without oxides being between them, which would inhibit their forming a thin intermetalic layer that connects them together.

Cleans the base metal(s) of the joint, both physically (floats crud away) and chemically (eats various things that would keep the solder form sticking), and prevents post-cleaning formation of an oxide layer that would keep the solder from sticking.

And most importantly, it gives you that wonderful "I'VE been SOLDERING!" scent.....:-)

Bob M.

Yeah, there is that factor, now that you mention it :)

"WAZ" wrote in news:1156269086.214924.162280 @b28g2000cwb.googlegroups.com:

IME, it has a tendency to warm parts through faster so you have to apply the soldering iron for less time to make a joint. It seems I sometimes get better joints when I use flux. (I'm not doing PC boards here, it's soldering wires to model railroad rail.)

It's also useful for "recharging" desoldering braid.

Puckdropper

That's because it aids the 'wetting' of the components that in turn leads to better thermal transfer.

Graham

Don't notice that at all with a Metcal.

GG