Printed circuit board manufacture
AssigneeEnthone Inc.
InventorsAndrew McIntosh Soutar, Peter Thomas McGrath
Life of this patent
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Abstract
A process used during manufacture of printed circuit boards comprises protecting metal pads and/or through-holes to provide a tarnish-resistant and solderable coating. In the method, the pads and/or through-holes are bright-etched, metal plated, preferably by an immersion process, and treated with a tarnish inhibitor. The tarnish inhibitor may be incorporated into the immersion plating bath. The metal plating is usually with silver or bismuth and the pads and/or through-holes comprise copper.
Claims31
A plating solution comprising:
- a solvent;
- metallic ions dissolved in the solvent;
- and
- a tarnish inhibitor in the solvent, the tarnish inhibitor characterized in that it does not cause the dissolved metallic ions to precipitate in the solution.
A silver-plating solution comprising:
- water;
- a source of silver ions dissolved in the water;
- and
- a tarnish inhibitor in the water at a concentration from 0.0001 to 5% by weight of the silver-plating solution, the tarnish inhibitor characterized in that it does not cause the dissolved silver ions to precipitate in the solution.
An aqueous plating composition suitable for forming an immersion plating of a first metal having a first electropositivity on a substrate formed of a second metal having a second electropositivity, the first electropositivity being greater than the second electropositivity, the composition comprising:
- ions of the first metal;
- a complexing agent for the ions of the first metal;
- and
- a tarnish inhibitor for the first metal, the composition being substantially free of any reducing agent for the ions of the first metal.
Dependencies are inferred from the claim text.