Fabrication and Characterization of Through-Glass Vias by the ECDM Process

Fabrication and characterization of electrodeposited copper filled through-glass vias (TGV) are demonstrated on full-scale fused silica wafer for the first time by a simple combination of electrochemical discharge machining and bottom-up copper electrodeposition. Due to lower cost and easy availability, stainless steel was chosen as tool electrode. Wire-EDM was used to create customized multi-tip tool electrodes that were used to create through-holes in a 520 μm thick fused silica substrate in less than 10 min. The average tool wear ratio was measured to be around 16. Due to the non-conductive nature of fused silica, these through-holes did not require any insulation and barrier layer and were filled with electrodeposited copper. I-V measurements of the TGVs showed a linear ohmic behavior. The Kelvin resistances of the fabricated TGVs were measured to be ranging from 242 mΩ to 275 mΩ. The average resistance of the fabricated Cu filled TGVs was 256 mΩ. The variation in the TGV resistance was less than ±8%. Due to its simplicity, this technique can be used in the fabrication of the integrated radio-frequency (RF) passive devices such as inductors and 3D packaging applications.