Machining of High-Aspect-Ratio Microelectrodes Using Micro-Electrical Discharge Machining-Based Self-Drilled Holes Technique

Micro Electrical Discharge Machining (micro-EDM) has the advantage of being a non-contact machining technique that allows it to machine high aspect ratio micro features in difficult-to-cut materials. The objective of this study was to explore the machining of highest possible aspect ratio microelectrodes using micro-EDM and determine the most suitable techniques, materials, and machining parameters to produce consistent, high-quality microelectrodes with smallest possible diameter and largest possible aspect ratios. Microelectrodes were fabricated using the self-drilled holes technique in which a hole is drilled in a piece of plate metal under conventional polarity (workpiece positive, tool negative), and then, the polarity is reversed to make the tool positive, thereby making it the “workpiece” and allowing the micro-EDM process to remove material from it. The electrode is then moved slightly off-center relative to the previously drilled hole, and the edge being fed into the plate is removed. This reduces the diameter of the electrode, and the process can be repeated until the electrode has reached the desired diameter and length. It was found that the self-drilled hole technique is capable of repeatedly producing electrodes with less than 50-micron diameter at the base, less than 20-micron diameter at the tip, and over 5 mm length which constitutes in aspect ratios of over 100. Using this method, it was possible to produce an electrode with tip diameter of 7.054 µm, base diameter of 73.64 µm, average diameter of 40.35 µm, length of 5.265 mm, and aspect ratio of 130, making it one of the highest aspect ratio electrodes reported in the literature using the micro-EDM based in-situ electrode fabrication techniques. Finally, the application of the fabricated high-aspect-ratio microelectrodes was demonstrated by successfully machining high-aspect-ratio micro-holes in a silicon wafer.