Solder Flux Manufacturer Explains the Function of Solder Flux

Solder flux is typically a mixture with rosin as the primary component and serves as an auxiliary material that ensures the soldering process proceeds smoothly. Soldering is a key manufacturing process for electronic components, and flux is the supplementary material used during soldering. Its main functions are to remove oxides from the surfaces of both the solder and the base metal, thereby achieving the required level of surface cleanliness; to prevent re-oxidation of the surfaces during soldering; to reduce the surface tension of the solder; and to enhance soldering performance. The quality of the flux directly affects the quality of electronic products. The following section, provided by a flux manufacturer, explains the specific roles and functions of solder flux.

I. What Do Solder Flux Manufacturers Say About the Role of Solder Flux?

The primary active ingredient in flux is rosin, which begins to decompose at around 260°C when exposed to tin; therefore, the solder bath temperature should not be set too high. Flux is a chemical substance that facilitates soldering and serves as an indispensable auxiliary material in soldering operations, playing a critically important role.

1. Folding and dissolving the oxide film on the weld bead

The surface of the base metal in atmospheric soldering is invariably covered by an oxide film with a thickness of approximately 2 × 10⁻¹⁰ to 2 × 10⁻⁸ meters. During soldering, this oxide film prevents the solder from wetting the base metal, thereby hindering the soldering process. To address this, a flux is applied to the surface of the base metal to reduce and remove the oxides, effectively eliminating the oxide film.

2. Folded Welding Base Material

The base material requires heating during the soldering process, and at elevated temperatures the metal surface oxidizes more rapidly; therefore, a liquid flux that coats the surfaces of both the base material and the solder can prevent oxidation.

3. Folding Brazing and Soldering Tension

The surface of the brazed joint exhibits a certain degree of surface tension, much like raindrops on a lotus leaf. This surface tension causes the molten solder to immediately form spherical droplets. Because of this surface tension, the molten solder cannot spread and wet the base metal surface effectively, thereby hindering proper wetting. However, when flux covers the surface of the molten solder, it reduces the surface tension of the liquid solder, significantly enhancing its wettability.

4. Foldable Protective Welding Masterbatch

The materials being welded have their original surface oxide layer compromised during the welding process. A high-quality flux, once the weld is completed, promptly resumes its function of protecting the base material. It efficiently transfers heat from the soldering iron to the solder and the solder’s surface. Moreover, an appropriately selected flux can produce aesthetically pleasing solder joints.

Second, solder flux manufacturers share the properties of solder flux.

1. The flux must have an appropriate operating temperature range. It should become active before the solder melts, remove oxide films during the soldering process, and reduce the surface tension of the molten solder. The melting point of the flux should be lower than that of the solder, but the difference should not be too great.

2. The flux must exhibit good thermal stability, with a typical thermal stability temperature of at least 100°C.

3. The density of the flux must be lower than that of the liquid solder, so that the flux can spread evenly over the brazed metal surface, forming a thin film that covers both the solder and the base metal, effectively isolating them from the atmosphere and promoting wetting of the base metal by the solder.

Summary by solder flux manufacturers: Residues from the flux must be non-corrosive and easy to clean; they must not release toxic or harmful gases. The flux must meet electronic-industry standards for water-soluble resistance and insulation resistance, exhibit no moisture absorption, and inhibit mold growth. It should also demonstrate chemical stability and be easy to store.