When ferric chloride is used as the etchant, no metal parts other than titanium can be used in the etching equipment. The process can be done in open trays but is much more effective if the etchant (often ferric chloride) is sprayed onto the metal. The engraving is usually made in copper or brass. It is also the same method used for printed circuit boards. This is used for intaglio printing plates or for decorative purposes. One method of photoengraving produces a shallow depression in the metal. A similar process called photolithography is used to make integrated circuits. In these applications, it is properly called photochemical machining, but the terms photochemical milling, chemical milling and photoetching are sometimes used.
A very high degree of precision is possible. It can be used to make flat springs, levers, gears and other practical components that would otherwise be fabricated from sheet metal by cutting, drilling, jigsawing or stamping.
It is also used to make nameplates, commemorative plaques and other decorative engravings. The same procedure is used to make printed circuit boards, foil-stamping dies and embossing dies. Photogravure and screen printing are examples of such process. In the graphic arts, photoengraving is used to make printing plates for various printing processes, reproducing a wide variety of graphics such as lettering, line drawings and photographs. The remaining photoresist is usually removed after the operation is complete. A solvent is used to wash away the soft parts, laying bare the underlying material, which is then bathed in or sprayed with the acid or other etchant. Typically, the photoresist is hardened where it receives sufficient exposure to light, but some photoresists are initially hard and are then softened by exposure. Alternatively, a lens may be used to project an image directly onto it. It is then exposed to light-usually strong ultraviolet (UV) light-through a photographic, mechanically printed, or manually created image or pattern on transparent film. It may be a liquid applied by brushing, spraying, pouring or other means and then allowed to set, or it may come in sheet form and be applied by laminating. Normally applied to metal, it can also be used on glass, plastic and other materials.Ī photoresist is selected which is resistant to the particular acid or other etching compound to be used. Photoengraving is a process that uses a light-sensitive photoresist applied to the surface to be engraved to create a mask that shields some areas during a subsequent operation which etches, dissolves, or otherwise removes some or all of the material from the unshielded areas.
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