Metallic coatings are stripped when parts are rejected after plating because of one or more of the following defects: 1. lack of deposit uniformity; 2. discoloration; 3. roughness; 4. lack of adhesion; 5. poor coverage; or 6. insufficient thickness. If the parts are valuable, reclamation via stripping and replating is feasible. Precious metals such as rhodium, gold, and silver are so valuable that even small quantities are worth reclaiming. In the printed circuit board industry, metallic resists such as tin or tin-lead are selectively stripped from contact tabs. The stripping should be done with as much care and planning as was required for the original plating process. Acids used in stripper formulations must be sufficiently strong to remove the deposit being stripped, yet should not appreciably attack the base metal. The chemical activity of a specific acid can usually be suppressed by limiting the water content in a system. This is accomplished by either using concentrated acids such as sulfuric, acetic, or phosphoric, which contain little water, or by adding organics such as glycerine to the acids instead of water. Chelating agents, which are specific for the metal being stripped, may be added to a stripping solution to prevent redeposition of the metal being stripped by immersion.
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