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 mu m 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 m Omega to 275 m Omega. The average resistance of the fabricated Cu filled TGVs was 256 m Omega. 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.