Process for silver plating in printed circuit board manufacture

摘要

In PCB manufacture, the pads and/or through-holes of a bare board are protected prior to mounting of other components by a silver plating process. The silver plate is applied from a plating composition by a replacement process in which silver ions oxidized copper and deposit a layer of silver at the surface. In the aqueous plating composition the silver ions are maintained in solution by the incorporation of a multidentate complexing agent. The compositions may contain a silver tarnish inhibitor and are free of reducing agent capable of reducing silver ions to silver metal, halide ions and substantially free of non-aqueous solvent. Surface mounted components can be soldered direct to the silver coated contact using any commercially available solder. Silver does not deposit onto solder mask, but only onto metal which is less electropositive than silver.;REEXAMINATION RESULTS;The questions raised in reexamination proceedings Nos. 90/012,336 and 90/009,934, filed Jun. 4, 2012 and Aug. 3, 2011 respectively, have been considered, and the results thereof are reflected in this reissue patent which constitutes the reexamination certificate required by 35 U.S.C. 307 as provided in 37 CFR 1.570(e) for ex parte reexaminations, and/or the reexamination certificate required by 35 U.S.C. 316 as provided in 37 CFR 1.997(e) for inter partes reexaminations.

主权项

1. A process for forming a silver coating on a surface of a first metal having a first electropositivity less than an electropositivity of silver, the process comprising a step of:
(a) contacting the surface of the first metal with an aqueous composition comprising silver ions and a complexing agent that is a multidentate ligand, the aqueous composition having a pH of from 2 to 12, to form a coating of silver on the surface of the first metal, wherein the aqueous composition is free of ammonium ions, thiosulphate ions and combinations thereof, said surface of said first metal having conductive metal pads, conductive metal through-holes or a combination thereof of a bare board, and in which the substrate includes non-metallic areas which remain uncoated in the process.