Pilot trials of immersion silver deposition using a choline chloride based ionic liquid

Purpose - The purpose of this paper is to present the optimisation of protocols for the immersion coating of silver onto copper-track printed circuit board (PCB) assemblies, using a novel class of ionic liquid and to show the implementation of the scale up process. Design/methodology/approach - Various conditions (temperatures and silver concentrations) are studied individually under laboratory conditions and then optimised for a pilot scale demonstrator line that is used to process British Standard test coupons. Findings - The use of these novel liquids for the immersion coating of silver produces silver dip coatings that are bright and even and which give solderability that is as good as the commercial aqueous, nitric acid based, electroless process without any solder-mask interface etching. Research limitations/implications - The combined technology has been optimised for an immersion silver coating line. Further development work should be undertaken to tailor the technology for gold immersion coating of PCB assemblies. Originality/value - The paper details a process in which no solder-mask interface etching is observed; that does not require the use of strong inorganic acids or expensive catalysts to sustain deposition and which does not appear to be light sensitive in contrast to other processes.