Many friends in the electronic soldering industry often confuse the concepts of flux, rosin and solder paste. In fact, the flux we usually say is a general term. In fact, rosin and solder paste are fluxes. Their use is Increase the reliability of soldering between the solder and the object to be welded during the soldering process. The main functions of the flux include wetting effect, removal of oxidation, auxiliary heat conduction, reduction of metal surface tension, and aesthetics of solder joints.

There are many kinds of fluxes on the market, which can be generally divided into the following three series:
(1) Inorganic series fluxes. In general, inorganic series fluxes have strong chemical action, and the welding performance is very good, but the corrosion effect is large and acidic. Flux. Because it is dissolved in water, it is also known as water-soluble flux, which includes inorganic acids and inorganic salts.
(2) Organic series flux (OA), the flux of organic series flux is between inorganic series flux and resin series flux. It is also acidic and water-soluble flux.
(3) Resin series fluxes, which are the most widely used in the soldering of electronic products, are resin-type fluxes. Since it can only be dissolved in organic solvents, it is also called organic solvent flux, and its main component is rosin. The main components of rosin are rosin acid and pimaric acid. Generally, it has a certain activity in neutral liquid rosin. It exhibits weak acid properties and reacts with metal surface oxides to form compounds such as rosin acid copper, which are suspended on the surface of the solder and used. It is non-corrosive and has strong insulation. Generally speaking, rosin is a commonly used flux.

Rosin is inactive in the solid state and is active only in liquid form. Its melting point is 127 ° C and its activity can last up to 315 ° C. The optimum temperature for soldering is 240 to 250 ° C, so it is in the active temperature range of rosin, and its welding residue does not have corrosion problems. These characteristics make rosin a non-corrosive flux and are widely used in electronic equipment. Welding. For different application needs, rosin flux has three forms: liquid, paste and solid. Solid flux is suitable for soldering iron, liquid and paste fluxes are suitable for wave soldering. In actual use, it has been found that when rosin is a monomer, the chemical activity is weak, and the wetting of the solder is often insufficient, so that a small amount of the active agent needs to be added to increase its activity.