To get a solid solder joint, it is necessary to remove the oxide film from the soldered surfaces and protect the metal from further oxidation during soldering. For this purpose there fluxes, which are usually multicomponent systems performing multiple functions. This surface cleaning, oxide removal, improved spreading of the solder and, as a consequence, increase the strength and density of connections.
Conventionally fluxes can be divided into orzhavlyayuschie and neorzhavlyayuschie (corrosive and noncorrosive, neutral), ie those that require rinsing after soldering good solder joint and those that do not, and even orzhavlyayut soldering can further protect it from corrosion. Moreover, fluxing agents conventionally divided into active and passive. Active fluxes contain in their composition substances which are actively interact with the metal surface is acid (salicylic, citric, phosphoric, etc.), zinc chloride, ammonium chloride, hydrochlorides of certain organic compounds, organic amines, glycerol. Passive (or weakly active) fluxes, is rosin, which is a mixture of organic acids, paraffin, mineral, vegetable and animal oils, fatty to-you. They removed the thin and unstable oxide film and contribute to the spreading of the solder.
With active solder fluxes from solid metal oxide film in most cases the active fluxes - orzhavlyayuschie. When soldering of printed circuit boards has a residual resistance value of flux, so even for a neutral, non-corrosive flux residue remover may be required.