Etchant

An etchant is a chemical agent used to remove material from a solid surface through a chemical reaction. Etchants are used to reveal microstructure, pattern surfaces, or strip coatings. They may operate by immersion, spraying, or, in some cases, electrochemical dissolution, and are often formulated to target a specific material or layer.

Etchants come in many forms, but most are liquids containing acids, bases, oxidizers, or complexing agents. Common bases include alkaline hydroxide solutions; common acids include nitric, phosphoric, and hydrofluoric acids. Buffered formulations control reaction rate and selectivity to minimize undercut and damage. Because many etchants are corrosive and toxic, handling requires appropriate safety measures and waste treatment.

Applications include electronics manufacturing, where etchants pattern copper or other metals; semiconductor device fabrication, where HF-based and buffered oxide etchants remove silicon dioxide; metallography, where etchants reveal grain structure and phases; and decorative metal etching for art and signage.

Common examples by material: copper — ferric chloride or cupric chloride in acid, and ammonium persulfate solutions; silicon dioxide — buffered oxide etch or HF-based solutions; steel — nitric acid in alcohol (Nital) or picric acid solutions; aluminum — phosphoric or related acid formulations.

Safety and environmental considerations are a key part of etchant use. Many formulations emit hazardous fumes, cause burns, or generate waste that must be neutralized and disposed of according to regulations.