Electrochimica Acta 49 (2004) 3997–4003 Spark assisted chemical engraving in the light of electrochemistry V. Fascio ∗ , R. Wüthrich, H. Bleuler Laboratoire de systèmes robotiques, EPFL, CH-1015 Lausanne, Switzerland Received 16 October 2003; received in revised form 21 December 2003; accepted 21 December 2003 Available online 5 June 2004 Abstract A novel technology for glass microstructuration called spark assisted chemical engraving (SACE) is presented. This technology is based on electrochemical discharge phenomena. Beyond a critical voltage, electrical discharges occur through the gas film around the electrode and the glass machining is possible. The SACE process is similar to the electrode effects. SACE has been analysed using an electrochemical approach (U–I plots), the experimental results clarify the onset of the discharge activity. Additionally, two theoretical models of the SACE phenomenon were introduced. Firstly a model, based on percolation theory, is briefly described and predicts the critical parameters (voltage and current). Secondly a method to estimate the spark’s characteristics (amplitude and duration) is presented and with the help of these data the machining depth was estimated by a numerical simulation. Finally, some glass microstructuring examples are presented to show the potential of this technology. © 2004 Elsevier Ltd. All rights reserved. Keywords: Spark assisted chemical engraving (SACE); Electrode effects; Percolation theory; Glass microstructuration 1. Introduction Since a decade, “lab-on-chip” devices and other minia- turised systems have known a great increase in the field of chemical analysis due to their economical interest. More re- cently the development of microreactors and micropumps, made of glass, have been achieved with the use of several materials processing techniques like HF etching [1], sand- blasting or laser machining. These technologies have limi- tations such as cost and machining time. Thus all these new products need new structuring technologies. Among the ex- isting technologies, electrochemical methods are emerging as cost-effective alternatives for the micro- and nanoma- chining of metallic parts. Indeed electrochemical machining (ECM) was developed in the late 50s and is now widely used in heavy industries such as aerospace for shaping oper- ations [2]. For the micro and nanostructuring, the promising electrochemical micromachining (EMM) was recently in- troduced by Ertl and co-workers [3] and allows high aspect ratio structures machining with submicron resolution [4]. The drawback for an extensive use of glass in microde- vices is its limited 3D structuring possibilities. In this paper, ∗ Corresponding author. Fax: +41-21-693-38-66. E-mail address: valia.fascio@a3.epfl.ch (V. Fascio). we discuss an original machining technology based on elec- trochemical phenomena: spark assisted chemical engraving (SACE). SACE was presented for the first time in 1968 by Kurafuji as electrical discharges [5] and allows glass ma- chining. Few literature is currently available on SACE and several names are given to describe SACE such as electro- chemical discharge machining [6], spark assisted etching [7] or electrochemical spark machining [8]. The main contribu- tions to the SACE research come from Asia (India, Japan) and Switzerland [6–9]. SACE can be described as follows. The sample to be machined is dipped in an electrolyte, typically sodium hy- droxide (Fig. 1). A constant DC voltage is applied between the machining-tool or tool-electrode (cathode) and the counter-electrode (anode). The counter electrode is a flat plate with a much larger surface than the tool surface (about a factor 100). When the applied voltage is below a critical voltage of about 25V, electrolysis occurs. Hydrogen gas bubbles are formed at the tool-electrode and oxygen bubbles at the counter electrode. As voltage is increased, current density rapidly increases too. The density and the mean radius of the bubbles increase and bubbles finally coalesce into a gas film around the tool-electrode. Light emission is observed in the gas film where electrical discharges occur between the tool and the surrounding electrolyte as can be 0013-4686/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2003.12.062