What are the functions of soldering iron flux?
Flux (FLUX) means "Flow in Soldering" in Latin. During the welding operation, the flux is like a flowing elf, which plays a role in accelerating the welding action.
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 regenerate an oxide layer. The oxide layer cannot be cleaned with traditional solvents and must rely on flux to interact with the oxide layer.
After the flux removes the oxide layer, the clean surface of the object to be soldered can be soldered.
Several chemical reactions between flux and oxides:
(1) Chemical interactions form a third substance;
(2) The oxide is directly stripped off by the flux;
(3) The above two reactions coexist.
The 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 and transparent substance that easily dissolves into unreacted rosin and is removed together with the rosin. Even if there is any 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 commonly used in the welding of semiconductor parts.
Almost all organic or inorganic acids can remove oxides, but most cannot be used for soldering.
2. Thermal Stability
When the flux removes oxides, it must also form a protective film to prevent the surface of the soldered object from being oxidized again until it contacts the solder.
Therefore, the flux must be able to withstand high temperatures and will not decompose or evaporate at the temperature of soldering operations. If it decomposes, it will form solvent-insoluble matter, which is difficult to clean with solvents. W/W grade pure rosin will decompose at around 280°C. Should require special attention.
3. Flux activity at different temperatures
A good flux not only has good thermal stability, but also must maintain good activity at different temperatures.
The function of flux is to remove oxides. Generally, the effect is better at a certain temperature. For example, RA flux. Unless the temperature reaches a certain level, chloride ions will not be desorbed to clean the oxides. Of course, this temperature must be at the temperature of the soldering operation. within the temperature range.
When the temperature is too high, its activity may be reduced. For example, rosin has almost no reaction when it exceeds 600℉ (315℃). This characteristic is used to purify the flux activity to prevent corrosion, but pay attention to the heating time in application. and temperature to ensure active purification.
The above introduces the function of flux and some precautions when using flux. I hope it will be helpful to everyone.
