Flux by functional classification: hand-dip soldering flux, wave soldering flux and stainless steel flux.
Stainless steel flux is a special chemical agent for stainless steel welding, the general flux can only be completed on the copper or tin surface welding, but stainless steel flux can be completed on copper, iron, galvanized plate, nickel and other types of metal welding; many kinds of flux, can be divided into organic, inorganic and resin three series.
1, Inorganic: Inorganic series of flux chemical effect is strong, welding performance is very good, but the corrosive effect is high, belong to acid flux.
Because it dissolves in water, it is also called water-soluble flux, which includes inorganic acids and inorganic salts.
Contains inorganic acid flux is the main component of hydrochloric acid, hydrofluoric acid, etc., containing inorganic salts of the main ingredient is zinc chloride, ammonium chloride and so on, they must be immediately after the use of very strict cleaning, because any residue in the welded parts of the halide will cause serious corrosion.
Inorganic series of flux is usually only used in the welding of non-electronic products, in the installation of electronic equipment is prohibited in the use of such inorganic series of flux.
The soldering function of the organic series flux is between the inorganic series flux and the resin series flux, it also belongs to acidic, water-soluble flux.
The water-soluble flux containing organic acids is based on lactic acid and citric acid, as its welding residues can be retained for a period of time without serious corrosion.
Therefore, it can be used in the installation of electronic equipment, but usually not in SMT solder paste, because it does not have the viscosity of rosin flux.
3, Resin: The largest proportion of the use of electronic products in welding is resin-type flux.
Because it can only dissolve in organic solvents, it is also known as organic solvent flux, the main ingredient is rosin. Rosin is inactive in solid state, only active when liquid, its melting point is 127℃ activity can continue to 315 ℃.
Solder welding is the best temperature of 240-250 ℃, so it is in the active temperature range of rosin, and its welding residue does not exist corrosion problems, these characteristics make rosin is not corrosive flux and is widely used in electronic equipment welding.
Rosin Flux has three forms of liquid, paste and solid state, the solid flux is suitable for soldering iron, liquid and paste flux is suitable for wave soldering.
When Rosin is monomer, the chemical activity is weaker and the wetting of the solder is often insufficient, so a small amount of active agent needs to be added in order to improve its activity. The flux of Rosin series is based on the strength of additive and chemical activity, it is divided into four kinds of inactive rosin, weakly active rosin, active rosin and super Active Rosin, the American Mil standard is called R, RMA, RA, RSA respectively, but JIS standard is divided into AA, A, according to the chlorine content of flux.
A, inactive rosin:
It is composed of pure rosin dissolved in a suitable solvent, where there is no active agent, the ability to eliminate the oxide film is limited, so it is required to have a very good weldability.
Commonly used in some use of the circuit is absolutely not allowed to exist corrosive hazards, such as implanted heart pacemaker.
B, weakly reactive rosin: The active agents added to this flux include lactic acid, citric acid, stearic acids and other organic and salt based organic compounds.
The addition of these weak active agents, can promote wetting, but the residue on the base material is still not corrosive, in addition to the high reliability of aviation, aerospace products or fine spacing surface installation products need to be cleaned, usually civilian consumer products do not need to set up cleaning procedures.
C, active rosin and super active Rosin:
In the active rosin flux, the addition of strong active agent hydrochloride, hydrazine hydrochloride and other salt-based organic compounds, this flux is significantly increased the activity, but the welding residue in the corrosion of chlorine ions become a problem that can not be ignored. With the improvement of the active agent, the active agent which can decompose residue into non corrosive substance at the welding temperature is developed, most of which are the derivatives of organic compounds.