Kester R520A is a lead-free, organic acid, water-soluble solder paste formula specifically designed for use with the higher temperature Pb-Free alternative soldering alloys such as Sn96.5Ag3.0Cu0.5 (SAC Alloys). The solder paste exhibits long stencil life and tack time, while still delivering exceptional solderability to a wide variety of metallic substrates. R520A was formulated to release consistently from the stencil for those critical fine pitch applications (0.5 mm/20 mils) with anti-slump characteristics and preferred solder deposit definition. The activator package in this formula is extremely aggressive, providing superior wetting to OSP coated and Immersion Gold over Electroless Nickel (ENIG) boards. R520A is an extremely stable water-soluble formula.