Flux breaks down metal oxides in the workpiece and at the same time prevents new oxides from forming during the subsequent heating, as oxygen is prevented from accessing the surface of the workpiece. In addition, flux reduces the surface tension of the solder used, so that a better flowability is achieved and thus a better bond to the workpiece. Finally, the flux shows when the workpiece is ready for soldering, namely when the flux is watery and clear, and at the same time the workpiece has the desired temperature. Most of the fluxes used for soldering are highly aggressive. It is therefore important that residues of the flux are carefully removed after soldering.
