Chemical and electrolytic etching have been in use as the fundamental technology in all areas of applications in electronics, precision machinery, and printing industries. In some application areas etching has been found obsolete by the emergence of more advanced technologies, but etching still remains to be an important processing technology. Some examples are introduced below.

(1)Thin film etching for circuit forming

Electronic circuits used for computers and communications equipment are comprised of printed circuit boards with integrated circuits, resistors, and capacitors of microscopic sizes. Demands for increased density for the integrated circuits require these resistor and capacitor components to become smaller year after year. For case of resistors as an example, conventional wire wound construction where a fine resistance wire wrapped around a insulator has limitations for miniaturization. To overcome the limitations, the resistors are now produced by etching a thin resistance film material formed on a insulator surface, where the etching produces a resistance circuit pattern with a desired resistance value on the insulator substrate.

For the resistance material, nickel/chrome alloys and tantalum film are typically used. The etchants used are mixtures of nitric acid, hydrochloric acid, and water.

Conventionally, the thin films are formed by a vapor deposition method such as sputtering, but electroless nickel plating and other methods are becoming popular in order to reduce the production costs.

For the electroless nickel plating, there are Ni-B alloy and Ni-P alloy types. A plating solution that uses sodium borohydride as a nickel redox agent produces a nickel alloy containing boron B, and a solution using sodium hypophosphite produces a nickel alloy containing phosphorus P. These nickel alloy films Ni2P, Ni3P, Ni2B, and Ni3B require considerably strong etchants for the etching processes since there would be some remaining phosphorus and boron smuts that are hard to etch. Typically, a solution of sulfuric acid, nitric acid, and water (1:1:1) heated to 40~50 deg. C is used. Therefore, the resist material used for protection of non-etched areas must also withstand this etching solution.

(2)Photo-etching use in printing industry.

Printing is a technology to transfer ink images such as characters, graphics, and photographs on paper, metal, or plastic surfaces, and requires printing plates.

Historically, printing technology has advanced through woodblocks, lead movable type, lithography, copper intaglio, and has now evolved into the photomechanical processes in use today. There are some type setting techniques in use for character printing, but graphics and photograph printing all rely on photo-etching technology. This is a technique of producing printing plates by creating concave or convex images of photos and graphics on metal plates. By photo-printing the acid resistant images on metal plates, then an etching process used to produce these printing images. For relief printing, zinc, magnesium, and copper are used for the metal substrates. These metal contain special metal additives to promote printing precision enhancements by reducing the sizes of metal crystals. For the etchants, nitric acid, water solution of sulfuric acid + hydrochloric acid, and in case of copper plates ferric chloride are used.