Definition

Etching removes unwanted copper using chemical solutions (etchants), leaving the protected circuit pattern. Common etchants include cupric chloride and alkaline ammonia. The process is either subtractive (start with full copper, etch away unwanted areas) or semi-additive (start with thin copper, pattern plate, flash etch). Etch factor describes the ratio of vertical to lateral etching; more lateral etch (undercut) limits fine-feature resolution. Spray etching provides better control than immersion. Etchant chemistry affects speed, copper recovery, and environmental impact.