Precleaning of soldered circuit cards to prevent white residue.

摘要

Following soldering of electrical components on a circuit card in a soldering process that includes use of an aqueous-based flux, the circuit card, containing the soldered electrical components, is exposed to a dilute aqueous basic solution prior to a final hot water rinse. The dilute basic solution prevents the formation of a white residue commonly associated with the use of aqueous-based fluxes. For example, using a flux consisting essentially of an aqueous solution of citric acid, and rinsing in either an aqueous ammonia solution consisting essentially of about 20 to 250 ppm ammonium hydroxide or an aqueous solution of about 0.1 to 3 wt% sodium bicarbonate, prevents formation of the white residue.