PRINTED CIRCUIT

electrical device in which the wiring and certain components consist of a thin coat of electrically conductive material applied in a pattern on an insulating substrate by any of several graphic art procedures. After World War II, printed circuits replaced conventional wiring in much electronic equipment, such as radio and television sets, computers and control equipment, and airborne and guided-missile electronic systems. They greatly reduced the size and weight of the equipment while improving reliability and uniformity over the hand-soldered circuits formerly used. Of the many techniques of manufacture, most involve photoetching or stencil etching. The insulating board is coated with copper and a protective film is deposited, photographically or by silk-screening, in the pattern desired for the circuit. The unprotected copper is then etched away either in an acid bath (for photographically deposited film) or by stencil-etching methods (for silk-screen film). The remaining conductive copper is left intact in the pattern of the circuit.