Scientific principle of rosin as flux

1. Because rosin contains organic acids such as rosin acid, in order to achieve a good solder joint, the welded object must have a completely oxide-free surface, but once the metal is exposed to the air, it will generate an oxide layer, which cannot be cleaned by traditional solvents. At this time, it is up to the flux to react with the oxide layer. After removing the oxide layer with flux, the clean surface of the object to be welded can be combined with solder;

2. There are several chemical reactions between flux and oxide: the third substance is formed by chemical action, and the oxide is directly stripped by flux, or the above two reactions exist at the same time. Rosin flux removes oxide layer, which is the first reaction. Rosin is mainly composed of rosin acid and isomeric diterpenoid acid. The flux reacts with copper oxide after heating to produce copper rosin, which is a green and transparent substance. It is easily dissolved in unreacted rosin and removed together with rosin, even if there is residue. It will not corrode the metal surface. Besides removing oxide layer, rosin has other important functions: preventing oxidation. After melting, it floats on the solder surface to form an isolation layer, thus preventing the solder surface from being oxidized, reducing the surface tension, increasing the fluidity of the solder and helping the solder to wet the weldment.