The Capabilities of Spark-Assisted Chemical Engraving: A Review

Abstract

Brittle non-conductive materials, like glass and ceramics, are becoming ever more significant with the rising demand for fabricating micro-devices with special micro-features. Spark-Assisted Chemical Engraving (SACE), a novel micromachining technology, has offered good machining capabilities for glass and ceramic materials in basic machining operations like drilling, milling, cutting, die sinking, and others. This paper presents a review about SACE technology. It highlights the process fundamentals of operation and the key machining parameters that control it which are mainly related to the electrolyte, tool-electrode, and machining voltage. It provides information about the gas film that forms around the tool during the process and the parameters that enhance its stability, which play a key role in enhancing the machining outcome. This work also presents the capabilities and limitations of SACE through comparing it with other existing micro-drilling and micromachining technologies. Information was collected regarding micro-channel machining capabilities for SACE and other techniques that fall under four major glass micromachining categories—mainly thermal, chemical, mechanical, and hybrid. Based on this, a figure that presents the capabilities of such technologies from the perspective of the machining speed (lateral) and resulting micro-channel geometry (aspect ratio) was plotted. For both drilling and micro-channel machining, SACE showed to be a promising technique compared to others as it requires relatively cheap set-up, results in high aspect ratio structures (above 10), and takes a relatively short machining time. This technique shows its suitability for rapid prototyping of glass micro-parts and devices. The paper also addresses the topic of surface functionalization, specifically the surface texturing done during SACE and other glass micromachining technologies. Through tuning machining parameters, like the electrolyte viscosity, tool–substrate gap, tool travel speed, and machining voltage, SACE shows a promising and unique potential in controlling the surface properties and surface texture while machining.