Photoetching

Photoetching, also known as photochemical machining (PCM) or photochemical milling, is a subtractive metal fabrication process that uses light to pattern a photosensitive resist on a metal sheet, allowing chemical etchants to remove unprotected regions and leave a finished part.

Process: The metal surface is cleaned and coated with light-sensitive resist. After drying, a photographic mask is applied and ultraviolet light exposes the resist in the desired pattern. The resist is developed to reveal the metal areas to be etched; a post-exposure bake may increase resist resistance. The sheet is immersed in an etchant chosen for the metal, and the exposed areas are dissolved away. Finally the remaining resist is stripped and the part is finished.

Materials and etchants: Common materials include copper, brass, nickel, stainless steel, aluminum, and foil. Etchants vary by material: copper etching typically uses ferric chloride or ammonium persulfate; other metals require different chemistries such as cupric chloride or nitric acid mixtures. The process can be performed with wet chemistry in open tanks or in controlled automation, and thicknesses range from a few micrometres to several tenths of a millimetre.

Characteristics: Photoetching is capable of producing complex, precise shapes with minimal tooling and fast turnaround, but etching is generally isotropic, causing undercut beneath the resist. This introduces challenges for tight tolerances and thick sections; compensation and masking strategies are used to achieve desired features.

Applications: Used for prototyping and low-to-mid-volume production of flat metal parts such as stencils, electrical components, PCB copper features, micro-mechanisms, aerospace shims, and decorative or jewelry parts.

Safety and environment: Involves caustic, corrosive chemicals and waste treatment; proper ventilation, handling, and disposal are required.