What exactly is Solder Flux?

[Picoflyer]

Hi everyone,
I am a newbie when it comes to soldering and was wondering: What exactly is 'Solder flux' and what is it used for?
Thanks
Dan

[slipstick]

Searching on Google for "Solder Flux" will find you an amazing amount of information. E.g. "The purpose of flux is to clean surfaces that are going to be joined together to enhance wetting by solder in the molten state. To accomplish this the flux must be able to deoxidize metal surfaces at high temperatures without decomposing."

The complete articale is at http://www.finishing.com/Library/flux.html

But most of the time the flux is simply contained within the solder we use. When you see "rosin-core" solder (almost all solder used for electronics) the rosin core is the flux. No extra flux is needed.

Steve

[KillerWatt]

It's like a "touch" of the magic harmless "stuff" that makes the difference between the metallic parts that you want pefectly soldered and stuck together or the solder just "beading-up" like water on an oilled surface and the parts never get soldered together......Just use a touch of the "correct" type flux in the "just right" ammount, and all the good things happen.......... kw

[Andy W]

Essentially, acid, which cleans the parts ready to take solder rather well..
..a

[vintage1]

Not always acid at all.

Totally depends on what surface contamination you are removing...

[Andy W]

"essentially"..
..a

[50+AirYears]

If you ever made the mistake of using an acid flux to solder electronic components, you would realize that there is a difference between acid fluxes and rosin fluxes. The action of a rosin or no-clean flux is more like a detergent that lifts the oxides and other contaminants from the metal surfaces.
Acid fluxes are ok for sheet metal work or plumbing, but are death to electronics. The best fluxes for electronics are either a good RMA or No-Clean flux. No-Clean seems sometimes to work best if you wet the joint to be soldered with a little Isopropyl Alcohol first.
Almost any of the electronics grade solders will have the flux inside the wire looking solder.