What is Photochemical Milling?
Photochemical milling, also known as “chemical milling” is a process for producing usually small flat parts from metal foils. The process has these steps: • 1. Pre-clean foil in preparation for photoresist application • 2. Apply photoresist, usually dryfilm, may be liquid • 3. Image photoresist • 4. Develop, usually using 1% Sodium or Potassium Carbonate solution • 5. Etch, most commonly using Ferric Chloride solution • 6. Strip Photoresist. Ferric Chloride is most often used, (if using Cupric Chloride etch, go here) and may be the least understood step in this process. Ferric Chloride will etch most metals, and is quite inexpensive, and fast, so it is the preferred etchant, but control of the chemistry of the etchant is crucial to consistent performance, and it is not an easily controlled chemical. The active content of the Ferric Chloride, is easily controlled, but is not the most important component of the etch. Ferric Chloride must have some amount of free Hydrochloric (also known
