Photo etching, or photo engraving, is a chemical milling process used to fabricate thin gauge precision metal parts. It uses a photoresist material instead of tape or elastomer for masking purposes. The process of photo etching can be used on virtually any commercial metal, including aluminum, copper, molybdenum, steel, and brass, but it is limited to a thickness range from .001” to 0.080” for maximum effectiveness.
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Process of Photo Etching
The photo etching process begins with the treatment of whatever part or sheet that is intended for etching. The part or sheet requiring acid etching is cleaned thoroughly and coated, or laminated, with a UV-sensitive photoresist. This is then developed through strategic exposure to light. The photoresist develops and hardens in the desired pattern or shape. The chemical reagent is then applied to the entire part. It can be applied using spray nozzles to further the efficiency of the process. The chemical washes away the unexposed masking layer, allowing contact with the parts of the metal part that are to be etched. The developed and hardened areas of the photoresist, however, protect certain areas of the metal part from corroding. The most common chemical used in the process of photo chemical milling is ferric chloride dissolved in hydrochloric acid. The etchant is left on the metal part for as long as is required to achieve the desired depth of cut, and then it is stripped off together with the remaining developed photoresist to reveal the etched part. The part can be re-cleaned and polished, and any irregularities can be burnished until the part is completely finished.
Benefits of Photo Etching
Parts manufactured with photo etching can be sized from .020” in diameter to 24” x 60”. The benefits of photo etching compared to standard chemical milling or manual engraving are substantial. The photoresist works a dual purpose of both protecting the metal where it is not to be etched, but also revealing the area to be exposed. This feature saves time in the manufacturing process. Chemical milling requires parts of the masking to be cut and removed, which can be a tricky process and can result in material wastage if not properly implemented. With photo engraving, or etching, the surface merely needs to be exposed to a pattern of targeted light and then exposed to the chemical reagent and rinsed. Tooling costs and maintenance remain relatively low, and processing times for completed parts are quick. Photo etching allows for photos or much more complex images to be engraved rather inexpensively, and it is often the only method that allows for very intricate designs to be etched in metal sheets, and parts or components machined using this method typically have very high tolerances and precise shapes. Photo etching can be a cost-effective and time saving alternative for many applications instead of laser or water-jet cutting, stamping, or wire electrical discharge machining.