Solder materials are indispensable in the production and maintenance of the electronics industry. Generally speaking, commonly used solder materials include tin-lead alloy solder, antimony solder, cadmium solder, silver solder, and copper solder.
The wire solder used in standard soldering operations is called rosin-cored solder wire or solder wire. Flux is added to the solder. This flux is composed of rosin and a small amount of active agent.
Flux is mainly composed of active agent (rosin, organic halide, etc.), surfactant (mainly high-efficiency surfactant such as alkane or fluorocarbon) and solvent.
In addition to the above components, different additives are often added to the flux according to specific requirements, such as film formers, antioxidants, corrosion inhibitors, matting agents, flame retardants, thixotropic agents, etc.
Rosin is neutral, low corrosive, will not corrode circuit components and soldering iron tips, its melting point is 127°C, and its activity can last up to 315°C.
The optimal temperature of solder is within the active temperature range of rosin. The main function of rosin is to remove the oxide film on the surface of the solder and the welding plate, so that the metal surface can achieve the necessary cleanliness.
Rosin can prevent the surface from re-oxidizing during soldering, reduce the surface tension of the solder, and improve the soldering performance. Therefore, the quality of the rosin in the flux will directly affect the quality of electronic products.
Rosin is a transparent, brittle solid natural resin, which is a relatively complex mixture, consisting of resin acids (abietic acid, pimaric acid), a small amount of fatty acids, rosin anhydride and neutrals. .
The main component of rosin is resin acid, accounting for about 90%, the molecular formula is C 19 H 29 COOH, and the molecular weight is 302.46. Resin acid is the most representative rosin acid, which is an unsaturated acid, contains conjugated double bonds, strongly absorbs ultraviolet light, and can be auto-oxidized or induced post-oxidation in the air.
The appearance of rosin is light yellow to light brown, with vitreous luster, with turpentine smell, density 1.060~1.085g/cm 3 . . It is amorphous, has no melting point, softening point (ring and ball method) is 72-76°C, and boiling point is about 300°C (0.67kPa). . Glass transition temperature Tg 30～38℃.
In conclusion, the longer the time and the higher the temperature, the lower the acid value of rosin, which is not good for daily welding work.
