Thin Glass Handling Solutions for Microelectronics Packaging

Glass substrates with fine-pitch through-glass via (TGV) technology gives an attractive approach to wafer level packaging and systems integration. Glass can be made in very thin sheets (<100 um thick) which aids in integration and eliminates the need for back-grinding operations. Electrical and physical properties of glass have many attractive attributes such as low RF loss, the ability to adjust thermal expansion properties, and low roughness with excellent flatness to achieve fine L/S. Furthermore, glass can be fabricated in panel format to reduce manufacturing costs. The biggest challenge to adopting glass as a packaging substrate has been the existence of gaps in the supply chain, caused primarily by the difficulty in handling large, thin glass substrates using standard automation and processing equipment. This paper presents a temporary bonding technology that allows the thin glass substrates to be processed in a semiconductor fab environment without the need to modify existing equipment.

Substrate Effects in GaN-on-Silicon RF Device Technology

The influence of the semiconducting Si substrate on the performance of GaN-on-Si RF technology is reviewed. Firstly, the formation of a parasitic conduction channel at the substrate-epitaxy interface is discussed in terms of its physical mechanism and its influence on RF loss, followed by schemes to minimize this effect. Secondly, it is shown that the presence of the parallel channel serves to backbias the III-nitride epitaxial stack and lead to current collapse even on the highly-resistive Si substrates used for RF device fabrication, analogous to GaN-on-doped Si power devices. Strategies to mitigate this issue are also presented and critically compared. Thirdly, thermal generation of carriers in Si at elevated operating temperatures leading to increased substrate loss is quantified, also followed by a discussion of possible techniques to reduce its influence on RF loss.