The role of flux in PCBA patch soldering

inPCBA patch weldingIn the process, the flux itself is not involved in the formation of welded joints. But it will affect the welding speed and the quality of the solder joints. It is similar to a catalyst in a chemical reaction. Like catalysts that trigger and promote chemical reactions, but do not participate in the formation of chemical reaction products, the role of flux in the PCBA soldering process can be summarized as follows:

1. Remove the rust film on the metal surface of the welded components.

2. Prevent the secondary oxidation of the metal surface of the components during the heating process. When PCBA is soldered, the metal surface of the component must be heated to a temperature at which the solder can be wetted.As the temperature continues to rise, the re-oxidation of the metal surface will also intensify. Therefore, the flux must provide protection for the metal surface of the purified components at the soldering temperatureFloor. That is to say, the flux should form a thin film on the metal surface of the entire component to cover the metal and isolate it from the air, so as to prevent it from being heated during the welding process.The role of secondary oxidation.

3. Reduce the surface tension of liquid solder. The flux in the soldering area of ​​the PCBA patch can affect the surface energy balance by promoting solder overflow. reduceThe surface tension of liquid solder reduces the contact angle.

4. Heat transfer. Generally, there are many gaps between the soldered components and the PCB board at the joint. During the PCBA patch welding process, the air in these gaps plays a role of heat insulation, thereby guidingCause poor heat transfer. If these gaps are filled with flux, heat transfer can be accelerated and thermal equilibrium can be reached quickly.

5. Promote the overflow of liquid solder. In the process of PCBA patch soldering, after the preheated viscous flux comes into contact with the solder, the activity will increase sharply, the viscosity will drop sharply, and the welding metalThe surface forms a second diffuse flow, and quickly spreads out on the metal surface of the welded component. The flow force formed by the second flooding process of the flux is added to the liquidOn the solder, thereby dragging the overflow process of liquid metal.