What is Flux?
Flux aids in soldering and desoldering processes by removing oxide films which form on the surface of metals being soldered. It increases the wetting ability of the solder, causing it to flow more uniformly over surfaces without balling-up (dewetting).
Flux is an essential material that aids in soldering and de-soldering processes by eliminating oxide films that form on the surface of metals being soldered. It increases the wetting ability of the solder and helps it flow uniformly over surfaces without balling-up. This article examines different types of fluxes available in the market and options for flux removal.
Rosin (type R) Flux
The oldest and most basic type of soldering flux is the natural rosin derived from pine tar resin. Pine tar resin is dissolved in solvent and then distilled to yield the clear, water-white rosin used in soldering flux. When used in this manner without the addition of acid activators, it is referred to as type R rosin flux. Activated fluxes can be either mildly activated or type RMA (rosin – mildly activated) or RA (rosin -activated), which are used to dissolve heavier oxide films, particularly those produced at higher soldering temperatures required for lead-free solder alloys. Activators commonly used include organic acids, halogenated (containing chlorine or bromine) compounds, amides, and monobasic and dibasic organic salts. However, these activators are corrosive and must be removed from the circuit board to ensure long-term reliability.
No-clean fluxes were developed to assist circuit board manufacturers in avoiding the time and expense of cleaning the board after soldering. They leave a smaller amount of residue than the conventional R type flux, which usually does not interfere with the operation of the board or cause long-term corrosion-related failures. They can be either made with natural rosin or contain synthetic resins, which impart the same desirable properties to the flux as the natural rosin product. However, the residues left by a no-clean flux may be sticky and attract dust or otherwise detract from the appearance of the circuit board, requiring removal (cleaning) to meet appearance or operation standards.
Water Soluble (Aqueous) Flux
Water-soluble fluxes are usually made with water-soluble resins, and their residues should be removed using a water rinse. Some water-soluble fluxes are water-based solutions, eliminating the need for using an alcohol-based flux solution. This helps reduce VOC emissions for board manufacturers operating under strict environmental regulations. Acid activators used in water-soluble fluxes include organic acids, halogenated (containing chlorine or bromine) compounds, amides, and monobasic and dibasic organic salts. However, these activators are corrosive and must be removed from the circuit board to ensure long-term reliability.
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