By preventing the formation of metal oxides, flux enables the solder to adhere to the clean metal surface, rather than forming beads, as it would on an oxidized surface. The role of flux is typically dual: dissolving the oxides already present on the metal surface, which facilitates wetting by molten metal, and acting as an oxygen barrier by coating the hot surface, preventing its oxidation.įor example, tin-lead solder attaches very well to copper, but poorly to the various oxides of copper, which form quickly at soldering temperatures. In high-temperature metal joining processes ( welding, brazing and soldering), flux is a substance that is nearly inert at room temperature, but which becomes strongly reducing at elevated temperatures, preventing oxidation of the base and filler materials. In some applications molten flux also serves as a heat-transfer medium, facilitating heating of the joint by the soldering tool or molten solder. įluxes are also used in foundries for removing impurities from molten nonferrous metals such as aluminium, or for adding desirable trace elements such as titanium.Īs cleaning agents, fluxes facilitate soldering, brazing, and welding by removing oxidation from the metals to be joined. These agents served various functions, the simplest being a reducing agent, which prevented oxides from forming on the surface of the molten metal, while others absorbed impurities into slag, which could be scraped off molten metal. Iron ore was also used as a flux in the smelting of copper. Some of the earliest known fluxes were sodium carbonate, potash, charcoal, coke, borax, lime, lead sulfide and certain minerals containing phosphorus. They are used in both extractive metallurgy and metal joining. Fluxes may have more than one function at a time. In metallurgy, a flux (from Latin fluxus 'flow') is a chemical cleaning agent, flowing agent, or purifying agent. Most soldering flux manufacturers and vendors also supply flux cleaners.Wire freshly coated with solder, held above molten rosin flux In case of fluxes that need cleaning after soldering, solvent cleaning or aqueous cleaners can be used. Soldering process ( Wave Soldering, Hand Soldering, SMT).Īfter the soldering process is over, it is important to clean the board to remove any unwanted flux residue that can affect the performance of the board and can even cause electrical short circuit.Density and type of Active and Passive Electronic Components to be soldered.Type of PCB (single-sided, double-sided, multilayer).Several factors determine the type of flux to be used during soldering: These are flux that doesn’t need any cleaning after soldering process.įlux Pen Choosing the Best Flux for Soldering However, they may be too aggressive, calling for extra precaution during cleaning of the PCB Assemblies to avoid flux contamination. They have good wetting action ( ability to remove oxides and prepare a clean surface for soldering). Water-soluble flux provides good soldering results because they have good flux activity. It is is primarily composed of organic materials other than rosin or resin. Water soluble flux is also known as organic acid ( OA) flux. Rosin Activated (RA) Flux: Type RA is most active of the rosin fluxes, and leaves the most residues after soldering.Rosin Mildly Activated (RMA) Flux: It has sufficient activator to clean the solder-coated or plated lands and component terminations or leads, thereby enabling the molten solder to wet these areas. It leaves virtually no residue after soldering. This type of flux is mostly used for surfaces that are clean.
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