Soldering process requires clean surfaces so the base metal is well exposed to the molten solder. During soldering operation, fluxes does the following:

1.	Remove the oxide films on the base metal.
2.	Momentarily prevent further formation of oxide films.
3.	Lower the surface tension of the solder to promote wetting.

Fluxes need to be removed after the soldering process since they tend to be corrosive. If they are not properly cleaned, they will eventually corrode the metals being joined, leading to product failures. For environmental reasons, the least aggressive flux should be chosen to do the job.