Effective soldering requires that metal surfaces are clean of passivating surface chemical layers. The flux must have the right chemistry to destroy surface passivation layers. Fluxes for soldering electronic PCBs require several features 1.To remove the passivation layers, make the metal surfaces active and wettable by the molten solder alloy.2.To protect cleaned surfaces with a layer of some substance, usually rosin, to prevent contact with air prior to application of the molten solder.3.To promote wetting of the surfaces to be joined by controlling the surface forces which determine the wetting process.4.To provide the right rheology for excellent paste printability, tack and slump characteristics.
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Although, the first function is the main one, for the PCB manufacturer good results can not be obtained if the flux does not perform the other functions satisfactorily. To be commercially viable, a flux must have all the properties that allow it to be used in common PCB manufacturing operations such as SMT. The properties that control requirements (1) to (4) above include chemical activity, activation temperature or window, thermal stability, surface tension, wetting power, rheology, print performance (for SMT), toxicity and nature/amount of residues. Oxford Solders range of fluxes and pastes are engineered with a deep knowledge of flux and paste chemistry and physics to fulfil all the necessary requirements for excellent performance in PCB manufacturing (SEE SOLDER PASTE ARTICLE ON THIS WEB SITE - UNDER LITERATURE).
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