Etchers and etching machines remove material from the surface of a part using an acid or alkaline chemical solution. Etchers and etching machines, also known as chemical milling machines, use masking substances to protect some surface areas of the part, providing selective material removal or patterning. Etching is commonly used to create printed circuit boards, semiconductors, solar cells, micro-electro-mechanical (MEMS) devices, and a wide variety of custom components. Etchers and etching machines include a wide range of equipment to provide a variety of services, including metal etching, glass etching, and stone etching; wet, plasma, and ion etching; polymer etching; and electropolishing. Etchers and etching machines use a combination of corrosive media to chemically remove material and masking material to protect specific areas from the etchants. Examples of corrosive media include acids or pickles, corrosive salts such as ferric chloride, caustic or alkaline solutions, corrosive gas or plasma, and solvents. The type of corrosive and masking materials used depends upon the etching application. For example, to manufacture semiconductor wafers, operators use a light-sensitive masking material called a photoresist and a strong corrosive, such as hydrochloric acid, to etch the surface of the wafer. Photoresists are masks that become soluble or insoluble to the etchant based upon their exposure to light. These types of etchers and etching machines use wet etching processes, using liquid-based corrosives and etchants. Semiconductor manufacturers also use plasma etching to pattern wafers. Plasma etchers and etching machines use highly energetic gases in a pressurized environment, causing neutrally charged particles from the gases to react with the surface of the wafer. Other specialized etchers and etching machines include ion milling or sputter etching machines, which use ions of noble gases to knock atoms off the substrate. Reaction-ion and deep reaction-ion etchers and etching machines are used to create very deep and narrow features on the surface of the semiconductor wafer. There are other types of etchers and etching machines that clean parts and components, remove scale or oxides, and prepare surfaces for coating, metal deposition, or patterning. They are used to produce components for the electronics, optics, photonics, aerospace, automotive, and marine industries. Etchers and etching machines can machine patterns onto the surfaces of a wide variety of parts such as filters, screens, encoder discs, microheaters, and the lead frames used for semiconductors. Certain specialized etchers and etching machines perform photochemical or electrochemical etching or electropolishing of components. In electrochemical or electropolishing techniques, a current is applied to accelerate the material removal process. In photochemical etching, light cured masks are used to protect specific areas from the etch solution, allowing surface patterning. Photochemical etching is commonly used to fabricate thin gauge sheet metal parts such as seals and gaskets, microwave circuits, sensors, springs, fuel cell components, and even jewelry.