Electrochemical discharge machining of a high-precision micro-holes array in a glass wafer using a damping and confinement technique

Abstract

Due to the unstable gas film, it is still a big challenge to achieve high repeatability and quality in electrochemical discharge machining (ECDM) of micro-hole arrays in glass. Based on our previous research on ECDM in micro channels, the present work uses a non-Newtonian fluid electrolyte (non-NTF electrolyte) in ECDM to further achieve a high uniform precision and quality micro-holes array in glass through the damping and confinement effect. The results revealed that an average entrance diameter of 343.8 ± 3.47 μm (mean ± standard deviation) and average heat-affected zone (HAZ) width of 18.01 ± 1.52 μm were successfully fabricated in a 300-μm-thick glass wafer. As compared to the conventional KOH electrolyte, the entrance overcut and the HAZ width of micro-holes were reduced by 43.84 %, and 64.81 %, respectively, while the repeatability improved by 67.92 %. The non-NTF electrolyte concentration and the tool rotation speed were also found to play a significant role in the damping and confinement effect, significantly affecting the geometrical properties of the micro-holes. Furthermore, the micro-holes array was filled with copper to form through glass vias (TGVs), and a standard deviation of the Kelvin resistance of TGVs was only 5.35 mΩ, further demonstrating an excellent repeatability and localization of ECDM micro-holes using a non-NTF electrolyte. The results illustrate that employing a non-NTF electrolyte is a simple way to increase the stability of the gas film and to improve the repeatability and localization of ECDM micro-holes.