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Thermal Characteristic and Performance of the Glass Interposer with TGV (Through-Glass Via)
Keywords: Glass interposer, Through glass via (TGV), Thermal Characteristics
Through-silicon via (TSV) technology for 3D IC has drawn significant attention in recent years. But, in another technology development front, the through-glass via (TGV), as also gained strong interest because of its pros and cons compared with the TSV. Although glass substrate may not be used for fabricating active devices like in silicon wafer, it may be a very good candidate to be used as an interposer because of its low manufacturing cost, good high-frequency performance, and small CTE mismatch. Nevertheless, one major drawback of TGV for feasibility is its thermal properties. Compared with TSV, the thermal conductivity of glass (k~1.38W/m.K) is much lower than that of silicon (k~148W/m.K); and the gap is about two magnitude orders. The quite low thermal conductivity of glass seems to make a big thermal issue for the TGV uses in 3D IC SiP integration. However, we argued the glass interposer with TGV is still feasible to the 3D IC SiP integration, because the very low thermal conductivity of glass should not be reflected to damage the thermal performance of the 3D IC SiP with TGV interposer. Theoretically, the interposer in 3D IC SiP just plays a role for heat transportation, and not for heat dissipation. In other words, the most heat of the chips would be directly dissipated to ambient via heat spreader, heat sink, or by exposing to ambient, and not via interposer. Therefore, we argued the glass interposer with TGV would not damage the thermal performance of a 3D IC SiP significantly compared to that of the SiP with a TSV silicon interposer. In this study, we used simulation to analyze the thermal characteristics of a TGV structure and a whole 3D IC SiP system. Also, the simulations would compare the single via thermal behaviors between TGV and TSV; and the 3D system thermal performance with TGV and TSV interposers. For via structure, the analysis show that a TGV and a TSV structure have a totally different trend of planar thermal conductivity (kxy): as density of through via (Dvia/P) increases, the kxy of TGV increases, but that of TSV decreases. As for the vertical thermal conductivity (kz), both TGV and TSV structures have obvious rising trends with increasing Dvia/P. For the thermal performance of 3D IC SiP system, we used a equivalent model to instead of a detailed model for simplification. The via structures of 30μm in diameter and 60μm in pitch are adopted in the case studies. The results show the thermal performance of the 3D IC system with TGV is slight worse than that of the system with TSV, but the both performances are nearly equal. The evaluations demonstrate the ultra-low thermal conductivity should not be reflected to damage the thermal performance of a 3D IC SiP with TGV interposer, and prove the feasibility of the glass interposer for the electronics applications.
Heng-Chieh Chien, Principal Engineer
Industrial Technology Research Institute
Hsinchu, Taiwan

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