Flux is used to prevent oxidation of the base and filler materials while soldering, as well as remove oxidation from the metals that will be joined. Flux also helps to wet the parts of the materials that are being joined together. During the soldering process, excess flux may form a blob at the location of the joint. Since most flux absorbs moisture and also chemicals, the soldered joints can become corrosive. You will need to clean the excess flux to prevent this from happening.
Things You'll Need
Wipe of the excess flux from the soldered joint with a piece of paper towel. Mix 1 tbsp. of baking soda with enough warm water to make a paste.
Apply the baking soda paste to the flux using an old toothbrush. The baking soda will act as a neutralizing agent.
Wipe away the baking soda and the dissolved flux from the soldered joint with a damp cloth, the let it air dry thoroughly.