Machining Processes - Photo Chemical Machining, Chemical Milling

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Photo Chemical Machining (also known as PCM or photo resist etching) is a chemical machining process whereby a photoresist ‘mask’ is applied to the surface of a part, often by printing. The mask protects the desired areas of the material to be kept. The material is then exposed to chemical baths, laser or light sources to etch away the material that has not been covered by the mask.

The broad term of etching covers a variety of machining methods. Photoresist etching applied no cutting or heating stresses to the part and can be used to perform machining on a microscopic scale, or to machine sensitive materials to which no stresses or heat affected zone is to be imparted..

The most common form of etching is used to cut profiles and shapes from thin sheet materials. Very finely detailed and intricate parts can be easily machined from sheet materials to a high degree of accuracy.

Another common application for photoresist etching is the production of printed circuit boards for the electronics industry. A blank PCB has the desired circuit tracks masked off and the unwanted material is etched away.

Chemical milling is also used to machine high strength components such as aerospace engine turbine blades as the chemical milling process imparts no cutting stresses o the material.

A slightly different form of photoresist etching often called photo-lithography is to be commonly found in the field of silicon wafer and MEMS structure manufacturing. The manufacturing process for building a silicon structure involves the alternating coating of silicon and metal films onto the surface of the wafer. After each layer, the surface is masked and the undesired material removed by chemical of laser etching. By continually applying a new layers of material and support material and etching off the unwanted material, microscopic structures can be built up to become silicon chips and MEMS structures.