Conductive Cu Paste as a Via Filling Material for Through Glass Via (TGV)

Yoshinori Ejiri, Masumi Sakamoto, Chiaki Shimizu, Naoyuki Kikuchi, Futoshi Oikawa, Masayoshi Nishimoto, Seiji Kai, Hiroshi Uragami
Resonac Co., Ltd.
Ibaraki, Japan

We developed a Cu paste that can be used as a filling material for a through-glass via (TGV). A TGV substrate can be filled with Cu paste without voids by using the vacuum-press method. A Cu film with the lowest volume resistivity of approximately 3.5 μΩ･cm was obtained at 350 °C or higher in a hydrogen atmosphere. Daisy chain samples were prepared using TGV substrates filled with Cu paste, and reliability tests were conducted.

The resistance changes of the daisy chain samples after the reliability tests [thermal cycle test (TCT) (-55/125 °C, 1000 cycles), high temperature storage test (HTST) (150 °C-1000 h, 260 °C-10 h), un-bias high accelerated stress test (HAST), pressure cooker test (PCT), and reflow cycle test (max. temp: 265 °C, 10 times, N2)] were within 3% of the initial value. Following electrolytic Cu plating, cracks occurred around the glass via. In contrast, the Cu paste was able to suppress the cracks in the via. The Young’s modulus of the sintered Cu paste was approximately 30 GPa, which is less than half of the Young’s modulus of the electrolytic Cu plating. The simulation results revealed that the low Young’s modulus of the Cu paste suppressed the cracks at the edge of the Cu terminal and on the inner glass wall of the via. We found that the Cu paste can be applied to TGV substrates as a filling material.

We have developed a Cu paste that can be used as a filling material for TGVs. The following key conclusions were drawn.

1. The film with the lowest volume resistivity of approximately 3.5 μΩ･cm was obtained at 350 °C or higher in the hydrogen atmosphere.
2. A TGV substrate can be filled with Cu paste without voids by using the vacuum-press method.
3. The rate of change in the conductive resistance of the substrate was found to be within 3% of the initial value after the reliability test.
4. We infer that the smaller difference in the CTE between glass and Cu is an important factor in preventing the generation of glass cracks.
5. The simulation results revealed that the low Young’s modulus of the Cu paste suppressed the cracks at the edge of the Cu terminal and on the inner wall of the via.