Method for etching thin foils by electrochemical machining to produce

Abstract

A process for etching a thin film or foil of an electrically conductive resistive material, preferably an alloy predominantly comprising nickel and chromium, by electrolytic etching under conditions of electrochemical machining above Jacquet's plateau on the I.V. characteristic curve. The process is particularly suitable for manufacturing a planar electrical resistor having a high stability, a low temperature coefficient, and a high ohmic value despite the relatively low resistivity of the film or foil. The anode surface polarization is maintained substantially constant over the surface of the foil or film by removing the by-products of the etching process, i.e., gases, viscous layers and other impurities, by mechanical effects such as an electrolytic flow or mechanical vibration, or both together. These mechanical effects are carefully balanced against the applied potential values such that the rate of formation of the layers and gases at the anode is equal to their rate of removal. Moreover, the anode electrical resistance is kept at a negligible value independent of the progress of the attack, by securing the film or foil to a thick layer of a conductor such as copper, whereby the evolution of potential drop across the foil, due to the electrical current flow, is kept at a negligibly small level. Under these conditions, a quasi-uniform etching is obtained all over the foil or film surface. The operating parameters of the process are also described as well as the advantages of the resistor produced according to the process of the invention.