What are the functions of soldering iron flux
1. Chemical Activity
To achieve a good solder joint, the object to be soldered must have a completely oxide-free surface. However, once the metal is exposed to the air, it will form an oxide layer. The oxide layer cannot be cleaned with traditional solvents, and must rely on flux to chemically interact with the oxide layer.
After the flux removes the oxide layer, the surface of the object to be soldered can be soldered and bonded.
Several chemical reactions between flux and oxides:
(1) Interaction chemical interaction to form a third substance;
(2) The oxide is directly stripped by the flux;
(3) The above two reactions coexist.
Rosin flux removes the oxide layer, which is the first reaction. The main components of rosin are abietic acid and isomeric diterpene acids. When the flux is heated, it reacts with copper oxide to form copper rosin ( Copper abiet) is a green transparent substance, which is easily dissolved into the unreacted rosin and removed together with the rosin. Even if there is residue, it will not corrode the metal surface.
The reaction of oxides exposed to hydrogen is a typical second reaction. At high temperatures, hydrogen and oxygen react to form water, reducing oxides. This method is often used in the welding of semiconductor parts.
Almost all organic or inorganic acids can remove oxides, but most of them cannot be used for soldering.
2. Thermal Stability
When the flux removes the oxide reaction, it must also form a protective film to prevent the surface of the soldered object from re-oxidizing until it contacts the solder.
Therefore, the flux must be able to withstand high temperature, and it will not decompose or evaporate at the temperature of soldering operation. If it decomposes, it will form solvent insoluble matter, which is difficult to clean with solvents. W/W grade pure rosin will decompose at about 280 °C. Should require special attention.
3. Flux activity at different temperatures
A good flux not only has good thermal stability, but must also maintain good activity at different temperatures.
The function of flux is to remove oxides, and generally the effect is better at a certain temperature, such as RA flux, unless the temperature reaches a certain level, chloride ions will not be decomposed to remove oxides, of course, this temperature must be within the soldering process. temperature range.
When the temperature is too high, its activity may be reduced. For example, rosin has almost no reaction when it exceeds 600°F (315°C). Using this feature, the activity of the flux is purified to prevent corrosion, but pay attention to the heating time in the application and temperature to ensure activity purification.
