An etching solution has been developed for use in removal of silver plating from polymer-based (including composite-material) structural components, the surfaces of which are intended to serve as mirrors and waveguide structures. Such structures are often plated with aluminum, copper, and silver to impart the reflectivity and electrical conductivity required of mirror and waveguide surfaces. It is sometimes necessary to remove the plating in preparation for reworking mirror or waveguide hardware. The present etching solution satisfies a need for an effective, fast-acting, nonoxidizing plating-removal solution that does not destroy the underlying polymeric or composite material.
The present solution is a modified version of a previously developed and widely used copper chloride etching solution. During use of the previously developed solution, the plating is attacked by nonoxidizing chloride ions. The previously developed solution works well in removing most metals but is not suitable for use on silver because it leaves an insoluble silver chloride residue.
The present solution is a bright green liquid that consists of deionized water containing 5 percent by weight of cuprous chloride and 20 percent by weight (saturation concentration) of ammonium chloride. The addition of the ammonium ions prevents the formation of an insoluble silver chloride residue. Instead, ammonium ions form a complex soluble salt with silver; namely, silver ammonium chloride [Ag(NH3)2Cl]. A silver-plated polymeric or composite-material surface can be cleaned of all silver by immersion in this solution for as little time as 10 seconds. The solution also readily attacks most other metals -- especially aluminum.
This work was done by Paul B. Willis of Caltech for NASA's Jet Propulsion Laboratory.