1. Chemical Activity

1. The formation of a third substance through chemical interactions;

2. The oxide is directly peeled off by the flux;

3. The above two reactions coexist.

2. Thermal Stability

When the flux removes the oxide reaction, it must also form a protective film to prevent the surface of the solder from being oxidized again until it comes into contact with the solder. So the flux must be able to withstand high temperatures and will not decompose or evaporate at the temperature of the soldering operation. If it decomposes, it will form solvent insoluble substances that are difficult to clean with solvents. Pure rosin of W/W grade will decompose at around 280 degree , which should be paid special attention to.

3. Activity of flux at different temperatures

When the temperature is too high, its activity may also be reduced. For example, when rosin exceeds 600 ℉ (315 degree ), there is almost no reaction. This characteristic can also be used to purify the flux activity to prevent corrosion. However, special attention should be paid to the heating time and temperature in application to ensure activity purification.