Without soldering flux, electronic equipment would be much more expensive to build.
Soldering and brazing are processes for bonding two or more pieces of heated metal together with a molten filler metal that forms an extremely strong bond. Flux is a chemical cleaner applied to the surfaces being soldered or brazed to remove all traces of oxidation from the heated workpieces and the molten filler metal. Otherwise, the oxides would block heat flow, producing a weak joint. Different types of flux exist for different joining jobs.
Inorganic Acid Flux
Inorganic acid flux is a blend of hydrochloric acid, zinc chloride and ammonium chloride. This type of flux is extremely active, used to solder copper, brass and stainless steel with a tin-lead alloy in household and commercial plumbing and in industrial applications. Acid flux requires thorough post-soldering cleanup of the joint to remove corrosive residue that could eventually weaken the joint. Acid flux comes as paste or liquid, or in acid-core solder that combines solder and flux in one. It cannot be used for electrical or electronic assembly work.
Rosin Flux
Rosin flux incorporates acidic compounds derived from conifer tree rosin, mixed with solvents. Rosin fluxes are used with tin-lead solder alloy for soldering electronic components because they don't leave corrosive residues. They do, however, leave behind a sticky residue that will attract moisture and dirt. The residue must be cleaned off with liquid solvents like trichloroethane. Rosin flux comes in paste or liquid or in rosin-core solder that combines flux and solder.
Organic Acid Flux
Since the 1940s, electronics assembly has increasingly turned to organic acid fluxes, developed by the Batelle Memorial Institute, for use with tin-lead solder. Organic acid fluxes are a blend of acids carried in alcohol or water without rosin, inorganic compounds or solvents. These fluxes have only about a third the solid matter of traditional acid or rosin flux. Sold only in liquid form, organic acid flux is used when rosin flux isn't active enough. Depending on formulation, organic acid fluxes either leave no residue or their residue washes away with water. Most liquid fluxes for electronic assembly are organic acid types.
Brazing Flux
Brazing is similar to soldering except it requires temperatures roughly double those needed for soldering. Brazing uses brass or alloys of nickel or silver as the bonding metal. Brazing also requires a flux that is extremely different from the fluxes used for soldering. Brazing flux is made up of potassium, boron, fluorine and sodium compounds, including potassium tetraborate, boric acid, potassium pentaborate, potassium biflouride, sodium dodecyl sulfate and boron, mixed with water as the carrier. Like soldering flux, brazing flux chemically cleans oxides from the metals to be joined.
Tags: acid fluxes, with tin-lead, Acid flux, comes paste, comes paste liquid, electronic assembly
