Electrochemical Micromachining

Abstract

The application of ultrashort voltage pulses between a tool electrode and a workpiece in an electrochemical environment allows the three-dimensional machining of conducting materials with submicrometer precision. The principle is based on the finite time constant for double-layer charging, which varies linearly with the local separation between the electrodes. During nanosecond pulses, the electrochemical reactions are confined to electrode regions in close proximity. This technique was used for local etching of copper and silicon as well as for local copper deposition.

Electrochemical Micromachining of Stainless Steel by Ultrashort Voltage Pulses

“…In particular the distance between the electrodes up to which the electrochemical reactions take place with a significant rate of removal of material, which is equivalent to the spatial resolution of the method, is expected to vary linearly with the pulse duration. This has been previously demonstrated for the machining of Cu [27] and is shown in the following within a slightly different experiment for the machining of stainless steel. For this purpose a cylindrical tool electrode was positioned 0.5 µm in front of the stainless steel surface.…”

“…In principle further reduction of the pulse duration is expected to lead to further improvement of the machining precision. Considering the high electrolyte concentrations employed for stainless steel, the ion concentration in the small gap between the electrodes allows for charging of the double layer down to gap widths even below 10 nm [27]. With pulses in the 100 ps range, such machining resolutions seem to be within reach.…”

“…The high frequency cell current and the pulse shape at the tool electrode were monitored with a real-time oscilloscope. Amplitude and shape of the cell current transient reflect directly the charging behavior of the double layer, i.e., the actual distance between tool and workpiece [27], and were used to in-situ check the machining process.…”

“…Recently we introduced a different approach, where electrochemical reactions are spatially confined with down to nanometer precision through the application of ultrashort voltage pulses [27,28]. This technique may help to bridge the gap between the versatility of the 'top down' and the precision of the 'bottom up' methods for three dimensional electrochemical microstructures.…”

“…As described in detail in Ref. [27] and Section 4, assuming typical DL capacitance and specific electrolyte resistance, pulses of a couple of 10 ns duration confine the charging of the DL to areas on the electrode surfaces, where the distance between the tool and the workpiece electrode amounts to less than a few micrometers. We achieved a machining precision of about 200 nm for the etching of stainless steel by 5 ns pulses as discussed later.…”