What remains as residue on the board after the soldering process. Depending on the flux specification and the operating conditions of the electronic assembly, residue can be critical or benign. So called “No-Clean” Fluxes leave residue which are not corrosive, and may be left untreated. Other fluxes, which contain acids or chlorides, leave corrosive residues. These fluxes need to be completely removed after soldering during a cleaning cycle, to avoid corrosive damage in the future of the product.