The functions of flux in PCBA processing plants during wave soldering process

Wave soldering flux is the main electronic auxiliary material used in electronic assembly PCBA processing. Its quality directly determines the reliability of subsequent products. The following is a brief description of the function of flux in wave soldering.

1. Remove the rust film on the surface of the metal to be welded. The rust film on the surface of the metal to be welded is usually insoluble in any solution, but the rust chemically reacts with certain materials to form a compound soluble in the liquid blasting agent, thereby removing the rust film and purifying the surface of the metal to be welded. This chemical reaction can cause the flux and the rust film to form another compound dissolved in the flux or flux solvent, or it can be chemical reaction that reduces the metal rust film to a pure metal surface. The flux belonging to the first chemical reaction is mainly represented by a rosin-type flux, and as an example of the second chemical reaction, some are reducing gases. For example, oxygen can restore oxides on metal surfaces at high temperatures, producing water and restoring pure metal surfaces.

2.Prevent secondary oxidation of the metal to be welded during heating. During wave soldering, as the temperature increases, the reoxidation of the metal surface is aggravated. Therefore, the flux must provide protection for the cleaned metal surface, that is, the flux should form a film on the entire metal surface to wrap the metal. It is insulated from the air to prevent secondary oxidation of the metal to be welded during the heating of the solder.

3. Reduce the surface tension of the liquid solder. The flux during the soldering process can affect the energy balance of the surface in a manner that promotes the flow of the solder, reducing the surface tension of the liquid solder, and reduces the contact angle.

4. Heat transfer. There are generally many gaps in the welded joint portion, and the air in these gaps acts as a heat insulating during the welding process, resulting in poor heat transfer. If these gaps are filled with flux, the heat transfer can be accelerated and the speed of the heat can be reached.

5. Promoting the flow of liquid solder. After the preheated adhesive flux contacts the wave solder, the activity increases sharply, the viscosity drops sharply, and a second flow is formed on the surface of the metal to be welded, and is rapidly spread on the surface of the metal to be welded. The diffusing force formed by the secondary flow of the flux is added to the liquid solder, thereby dragging the flow process of the liquid metal.

The flux coating system applies the flux automatically and efficiently to the soldered surface of the PCB, using a flux to break the oxide layer and removing the loose oxide layer from the metal surface, allowing the solder to directly contact the base metal.