Application of Flux in Wave Soldering in PCBA

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Wave soldering flux is a crucial electronic auxiliary material used in the assembly process of printed circuit boards (PCBA). The quality of the flux directly influences the reliability of the final product. Below is a brief overview of the role of flux in wave soldering.

1. Rust Film Removal: The flux effectively removes the rust film from the surface of the metal being soldered. This rust film is typically insoluble in most solutions; however, it can be eliminated through chemical reactions with specific materials, producing compounds that dissolve in the flux or its solvent. These reactions either create a solution with the rust film or reduce the rust to reveal a pure metal surface. Rosin-type flux is an example of the first type of reaction, while certain reducing gases exemplify the second. For instance, oxygen can reduce metal oxides at high temperatures, generating water and restoring the pure metal surface.

Application of Flux in Wave Soldering in PCBA

2. Prevention of Secondary Oxidation: During the wave soldering process, the metal surface can become re-oxidized as the temperature increases. Therefore, the flux must protect the cleaned metal surface by forming a film that wraps around the metal, isolating it from the air and preventing secondary oxidation during welding.

3. Reduction of Surface Tension in Liquid Solder: The flux plays a role in affecting the energy balance on the surface, promoting the flow of solder by reducing the surface tension of the liquid solder and decreasing the contact angle.

4. Heat Transfer: Gaps often exist in the welded joint, where air can act as an insulator, hindering heat transfer. Filling these gaps with flux can enhance heat transfer, allowing faster thermal balance during the welding process.

5. Promotion of Solder Overflow: Upon contact with the wave solder, the viscous flux dramatically increases in activity, leading to a significant drop in viscosity. This results in the formation of a second overflow of flux over the metal surface, which spreads rapidly. The overflow force generated during this process helps facilitate the flow of liquid solder.

By understanding these functions, it is clear that flux is essential for achieving effective and reliable wave soldering in electronic assemblies.

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