What are the types of flux

2021-09-08 00:00

Fluxes are classified according to their functions: hand dip soldering flux, wave soldering flux and stainless steel flux; the first two are familiar to the majority of users, here is the explanation of stainless steel flux, which is a chemical agent specially for stainless steel welding , general welding can only complete the welding of copper or tin surface, but stainless steel flux can complete the welding of copper, iron, galvanized sheet, nickel plating, various stainless steel, etc.; there are many types of flux, which can be roughly divided
into There are three series of organic, inorganic and resin.
Resin flux is usually extracted from the secretions of trees, which is a natural product and is not corrosive. Rosin is the representative of this type of flux, so it is also called rosin flux.
Since flux is usually matched with solder, it can be divided into soft solder and hard solder corresponding to solder.
Soft fluxes such as rosin, rosin mixed flux, solder paste and hydrochloric acid are commonly used in the assembly and maintenance of electronic products, and should be selected according to different welding workpieces in different occasions.
There are many kinds of fluxes, which can generally be divided into inorganic series, organic series and resin series. Inorganic series flux
Inorganic series flux has strong chemical action and very good fluxing performance, but it has a strong corrosion effect and belongs to acidic flux. Because it dissolves in water, it is also called water-soluble flux, which includes two types of inorganic acids and inorganic salts.
The main components of fluxes containing inorganic acids are hydrochloric acid, hydrofluoric acid, etc., and the main components of fluxes containing inorganic salts are zinc chloride, ammonium chloride, etc. They must be cleaned very strictly immediately after use, because any residual Halides on weldments can cause severe corrosion. This kind of flux is usually only used for soldering of non-electronic products, and it is strictly forbidden to use this kind of inorganic flux in the assembly of electronic equipment.
The fluxing effect of organic
organic series flux is between inorganic series flux and resin series flux, and it is also acidic and water-soluble flux. Water-soluble flux containing organic acids is based on lactic acid and citric acid. Since its soldering residue can remain on the soldered object for a period of time without serious corrosion, it can be used in the assembly of electronic equipment, but it is generally not used in In SMT solder paste, because it does not have the viscosity of rosin flux (to prevent the movement of SMT components).
Resin series
The proportion used in the soldering of electronic products is resin-type flux. Because it can only dissolve in organic solvents, it is also called organic solvent flux, and its main component is rosin. Rosin is inactive in solid state and active only in liquid state. Its melting point is 127°C and its activity can last up to 315°C. The soldering temperature is 240-250°C, so it is within the active temperature range of rosin, and its soldering residue does not have corrosion problems. These characteristics make rosin a non-corrosive flux and are widely used in the welding of electronic equipment .
For different application needs, rosin flux has three forms: liquid, paste and solid. Solid flux is suitable for soldering iron soldering, while liquid and pasty fluxes are suitable for wave soldering respectively.
In actual use, it is found that when rosin is a monomer, its chemical activity is weak, and it is often not sufficient to promote the wetting of solder. Therefore, it is necessary to add a small amount of activator to improve its activity. Rosin series flux is divided into four types according to the presence or absence of activators and the strength of chemical activity: non-activated rosin, weakly activated rosin, activated rosin and super-activated rosin, which are called R and RMA respectively in the American MIL standard. , RA, RSA, and the Japanese JIS standard is divided into AA (0.1wt% or less), A (0.1~0.5wt%), B (0.5~1.0wt%) three grades according to the chlorine content of the flux.
① Non-activated rosin (R): It is composed of pure rosin dissolved in a suitable solvent (such as isopropanol, ethanol, etc.), there is no active agent in it, and the ability to eliminate the oxide film is limited, so it is required to have very Good solderability. It is usually used in some circuits that absolutely do not allow the risk of corrosion in use, such as pacemakers implanted in the heart.
②Weakly activated rosin (RMA): The activators added to this type of flux include organic acids such as lactic acid, citric acid, and stearic acid, as well as basic organic compounds. After adding these weak active agents, wetting can be promoted, but the residue on the base material is still not corrosive, except for aviation and aerospace products with high reliability or surface mount products with fine pitch that need to be cleaned, general civil use Consumer products (such as tape recorders, televisions, etc.) do not need to have a cleaning process. When weakly activated rosin is used, there are also strict requirements on the weldability of the welded parts.
③Activated rosin (RA) and super-activated rosin (RSA): in the activated rosin flux, the strong activators added include basic organic compounds such as aniline hydrochloride and hydrazine hydrochloride. The activity of this flux is It has been significantly improved, but the corrosion of chloride ions in the residue after welding has become a problem that cannot be ignored, so it is generally rarely used in the assembly of electronic products. With the improvement of activators, activators that can decompose residues into non-corrosive substances at welding temperature have been developed, most of which are derivatives of organic compounds.

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