Solder Flux is a chemical cleaning agent used when soldering electronic components onto printed circuit boards. It is used in both manual hand-soldering as well as the different automated soldering processes used by PCB supplier China.

Printed Circuit boards produced by PCB supplier China usually have copper traces which can oxidize when exposed to air or get contaminated while handling the board. This can prevent the formation of good solder joints. In order to remove this contamination and avoid oxidization, it is crucial that the board is cleaned with flux prior to soldering. Flux can be used to clean and remove these oxides and other impurities from the board.

Physically, Solder flux can be solid, semi-solid, or a liquid. It is usually available as a paste in jars/tin/cans. It is also available as a liquid in bottles. Flux-pens are generally used to apply flux when hand soldering.

Most often, a solder flux is available as an adhesive-like chemical compound nature and is responsible for holding the components in place until the reflow process. The flux also protects the metal surfaces from re-oxidation during soldering. The flux contains additives to improve the flow characteristics of the molten solder and thus helps in wetting of the board.