Large-body-sized Glass-based Active Interposer for High-Performance Computing

This paper presents a next generation glass-based active interposer with 2 micron polymer RDL. Passive 2.5D interposers have become a mainstream solution to address the bandwidth demands of high-performance computing (HPC) applications. However, such passive interposers face challenges in meeting future performance, cost and reliability needs and active interposers have been studied recently as a means of scaling interposer performance. Given the ability to grow CMOS on Silicon more readily, only Silicon has been studied as substrate core for active interposers. However, for large body sizes, Silicon is not cost effective and interconnects tend to be lossy over long distances. Glass has been explored as a passive interposer core previously, and glass-based panel embedding (GPE) solutions have also been developed for fanout applications. This work uses GPE technology to demonstrate a glass-based active interposer substrate with potential for large-body-sized packages. The key challenge, however, in achieving a wiring density of over 250 IO/mm is the surface non-coplanarities associated with cavities in glass substrates. This paper describes the fabrication process for a Glass-based active interposer with dies embedded in glass cavities, and a systematic parametric process optimization to improve the surface planarity to demonstrate 2 micron L/S RDL on die-embedded glass substrates.