Glass micro-machining by glow discharge electrolysis
Beside silicon, glass is the most important material used in the constantly growing field of micro-devices. Several applications need glass because of its unique properties: chemical resistance, transparency, low electrical and thermal conductivity, and biocompatibility. Some of these devices are: micro-accelerometers, micro-reactors, micro-pumps, and medical devices. The limiting factor for increasing the usage of glass in micro-devices is its limited structuring possibility. Chemical etching technologies (such as with hydrogen fluoride) are well established, but remain too slow and expensive for many industrial applications. Other technologies are available, such as laser machining or mechanical machining (ultra-sonic or powder blasting). Both are hampered by the difficulty in obtaining good surface quality and the potential for structural damage. In general, high aspect-ratio structures are a challenging problem. A possible answer is Spark Assisted Chemical Engraving (SACE).
SACE, also known in the literature as Electro Chemical Discharge Machining, or ECDM (not to be confused with Electro Discharge Machining and Electro Chemical Machining for Conductive Materials, two processes that are also referred to as ECDM in combination), is based on electrochemical discharges. The principle is simple: the work-sample and two electrodes are dipped into an electrolyte (typically aqueous NaOH). The cathode is used as a tool. When applying a voltage higher than a critical value (typically 30V) a gas film around the tool is formed by coalescence of the bubbles growing on its surface. Electrochemical discharges occur between the tool and the electrolyte. The heat generated locally promotes etching of the work-sample. SACE needs neither clean-room facilities nor mask fabrication, unlike most micro-machining technologies.
Today, one-dimensional SACE drilling is well characterized in open loop operation. However, no control strategy has been reported. Developing feedback strategies would open new possibilities for SACE machining, helping to overcome its main limitations.
The aim of the proposed project is to develop drilling strategies based on force-feedback control.
