These fluxes contain. Dissolved in the rosin, a small proportion of complex substances €œactivators€. The properties of the substances have been carefully chosen so that, on raising the flux to the soldering temperature, a small controlled quantity of a special reagent is liberated. This dissolves away the metal oxides and so promotes the flow of molten solder over the clean metal surface. Most of the reagent is either destroyed by combination with the metal oxide, or by the soldering heat. Any small quantity remaining in the flux is rendered innocuous by a re-combing with the activator, and so the flux residue is, like pure rosin, non-corrosive, hard, non-sticky and impervious to moisture.
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