Precision Etching of Thick-Film Circuits of Aluminum and Aluminum-0.1 Wt% Copper

摘要

In certain high-current applications the resistance of the aluminum conductors is an important design parameter. Such a case is the aluminum exploding-bridge used in some nuclear detonators. The resistance of the network must be accurately known so that the individual bridge will receive the proper firing current. Vapor-deposited, thick aluminum films (0.011 mm) are often used to produce the necessary circuitry. These films are suitably masked and etched to make the conductors. Conventional etching methods for aluminum or aluminum-0.1 wt percent copper do not yield conductors with a well-defined, reproducible cross section. This results in unacceptable variations in electrical resistance. For this application, we have developed a new etching solution that contains 25 to 50 vol percent polyphosphoric acid, 75 to 50 vol percent orthophosphoric acid, and 10 to 30 g/l ferric chloride. Etching may be done at 55 to 65 exp 0 C, but for precision etching the temperature should be controlled to +-1 exp 0 C. The solution is useful for dip etching of aluminum circuits. The paper describes some limited production experience with this etch. (ERA citation 03:050663)