Through-holes micromachining of alumina using a combined pulse-feed approach in ECDM.

Micromachining of alumina has gained a lot of interest due to unique combinations of electrical resistivity and good thermal conductivity, thus being a potential substrate for microsystems packaging in high-power electronics. Creating multiple through-holes simultaneously in alumina is difficult due to its hard and brittle nature. In this article, the formation of multiple through-holes in a 425 µm thick alumina substrate is demonstrated for the first time using the combined pulse-feed approach of the ECDM process with multi-tip array tool to improve productivity. Initial experiments are conducted with a single-tip electrode to understand the effect of duty factor, pulse frequency, and feed rate. A combined pulse-feed approach is adopted to create deep microholes (>600 µm). Later, multiple through-holes are formed using 3 × 3 multi-tip array tool to achieve an average etch rate of 24 µm/min using the combined pulse-feed approach. A duty factor of 70% and a pulse frequency of 20 kHz are suggested for stable electrochemical discharge. A low feed rate (<1 µm/s) is recommended to avoid physical contact between the tool and workpiece. These multiple through-holes can be filled with electroplated copper to form 3D interconnects for upcoming radio-frequency MEMS applications. [ABSTRACT FROM AUTHOR]