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soldering flux[′säd·ə·riŋ ‚fləks]
a nonmetallic substance used to remove oxide film from solder and the surface of the material being soldered; this prevents the formation of oxide during soldering and also reduces the surface tension of the solder. Fluxes may be powders, pastes, or water, alcohol, or glycerine solutions. Their effect appears only within a certain temperature range. Some fluxes can be used successfully in soldering a variety of materials, whereas others have highly specialized purposes. The most universal fluxes for the high-temperature soldering of steels and copper alloys are those based on Na2B4O7 and H3BO3; for low-temperature soldering, the most universal flux is based on ZnCl2. A flux that is widely used in soldering aluminum alloys contains 8 percent ZnCl2, 10 percent NaF, 32 percent LiCl, and 50 percent KC1.