The solvent of choice

This paper outlines the current position of water based no‐clean liquid fluxes for wave soldering. The primary differences between these and “traditional” alcohol based liquid fluxes are explored using wetting balance methods. Reduced wetting capability (of the flux onto the PCB) can be addressed by using various surfactant additives; improved solderability is due to enhanced acid activator dissociation resulting from increased solvent polarity. Regarding implementation in a production environment, there is only minor impact. A slightly increased preheat capability is required, and foam application demands tight control of the feed gas flow rate. More generally, in addition to the “headline” environmental benefit of reduced VOC emissions, water based liquid fluxes confer significant handling advantages, for example zero flammability and low odour/evaporation at room temperature. Against this background, it is suggested that water based liquid fluxes will become ever more popular.