The Kester 959 is a no-clean, non-corrosive liquid flux that is designed for the wave soldering of conventional and surface mount circuit board assemblies. 959 was developed to minimize the formation of micro-solder balls during wave soldering operations. 959 leaves evenly distributed residues for the best cosmetic appearance. - This flux contains a small percentage of rosin (1%), which improves solderability, heat stability and surface insulation resistance. 959 offers the best wetting and the shiniest solder joints of any no-clean, solvent-based chemistry.