Glass Core Substrates: From R&D breakthrough to platform technology

The semiconductor industry is entering a new era in which advanced packaging determines the pace of innovation as much as transistor scaling ever did. As compute engines for High-Performance Computing, AI, and communications technology grow in size and complexity, conventional organic laminates face limits in warpage, line/space miniaturization, and dielectric loss. Glass, long valued for optical properties, flatness and stability, is now stepping up as a core material in IC substrates. AT&S is one of the key innovators in the development of this new technology and pushes the boundaries of current packaging solutions with its European partners in the IPCEI ME/CT (Important Project of Common European Interest on Microelectronics/Communication Technology).

Multiple analyses converge on glass as a credible platform for advanced microchip packaging technologies like multi-die integration and co-packaged functions. Compared with organics, glass exhibits exceptionally low total thickness variation (TTV) and can achieve very low warp, while its dielectric properties reduce losses and crosstalk at high frequencies. These advantages are key for AI accelerators, datacenter networking, and 5G/6G infrastructure. AT&S has long been an active player in researching next-generation solutions for high frequency applications and High-Performance Computing (HPC) and is one of the few microelectronics companies that is already working on integrating glass technology into its manufacturing processes.

AT&S’s new Competence Center for R&D and IC Substrate Production in Leoben, Austria, which was supported by funding from the European Union’s IPCEI ME/CT, and several ongoing research initiatives within the company’s international manufacturing network have positioned AT&S at the forefront of advanced packaging research, with Glass Cores being a key focus. At the same time, the supply chain ecosystem’s readiness is increasing. Materials suppliers are maturing glass formulations and panel formats tailored to packaging, and device makers and substrate suppliers are piloting Glass Core substrates and interposers.

“We have been doing a lot of work on Glass Cores in recent years to explore its utility for manufacturing on bigger panels, integrating new functionality into our substrates, and providing new ways to handle applications that demand high currents or voltages. Our new Substrate Competence Center in Leoben will provide a significant boost for our glass program and we are already partnering with renowned semiconductor manufacturers to develop prototypes,” says Markus Leitgeb, Head of Research BU ME at AT&S.

Glass is different

Several properties make glass especially attractive for advanced packaging and high-bandwidth communication: Glass can be engineered with a thermal expansion coefficient close to silicon, reducing thermomechanical stress and warpage during assembly and thermal cycling. Prototypes demonstrate low warp and ultra‑smooth surfaces that benefit lithography and fine‑pitch bumping.

As a high-resistivity insulator with low loss tangent, glass preserves signal integrity at multi-GHz to mmWave frequencies and reduces parasitics in high-speed channels compared with organic dielectrics. This is why glass appears in roadmaps for RF, photonics, and high-bandwidth chiplets.
Unlike silicon interposers, glass can be formed in large panels that align with advanced packaging lines. One of the most exciting prospects for Glass Core substrates lies in copackaged optics, the integration of photonic components directly into the package. The material offers optical transparency, low surface roughness, and dimensional stability, making it an ideal medium for embedding optical interconnects alongside electrical redistribution layers, dramatically reducing latency and power consumption in datacenter and AI systems.

How a Glass Core substrate is built

Turning a sheet of glass into an advanced substrate requires precision micromachining. Through-glass vias (TGVs) provide vertical power and signal paths. Metallization can involve full copper fill or sidewall plating with dielectric infill, each with distinct stress and reliability tradeoffs. Industrial demonstrations show strong progress on via quality, strength, and reliability under thermal cycling. On one or both sides of the glass, copper routing is patterned on build-up layers using semi-additive processes to achieve fine line/space and high density fanout.

Where glass will matter

AI and High-Performance Computing accelerators need large IC substrates, vast pin counts, low-loss links, and clean power delivery. This is an ideal fit for glass’s flatness, fine-structuring potential, and excellent electrical properties. Early industry demonstrations of Glass Cores and interposers have specifically targeted multi-die GPUs/CPUs and memory-rich systems.

High Frequency/mmWave technologies and photonics also stand to benefit. Glass offers low losses and optical transparency, enabling cleaner radio frequency frontends and potential electrooptic integration at the package level. Vendors have documented low warp, high insulation resistance, and hermetic TGVs for rugged environments. These are perfect ingredients for automotive radar, communications infrastructure, and sensor modules. Finally, panel-level integration for large form factors aligns with the industry’s migration to square panels to improve throughput and yield for big, chiplet-heavy assemblies.

The hard parts

AT&S is currently tackling several hurdles to real-world deployment. As glass gets thinner for advanced packages, fracture mechanics and edge strength become critical; new tooling and process controls are required along the entire line. Moving to large, flat panels stresses handling and inspection systems. Bringing glass to volume requires either retrofitting existing lines or investing in new equipment. While multiple glass suppliers can deliver tailored formulations and structured panels, end-to-end readiness, from via formation to redistribution layers, bonding, testing, and reliability standards, must mature. The intellectual property landscape also tells a story: patenting has accelerated since 2020, with intense activity from device makers and materials companies. This is a signal of both promise and competition.

Advantage AT&S

AT&S is one of the world’s leading manufacturers of high‑performance IC substrates, supplying top compute customers around the world from its manufacturing and research hubs in Europe and Asia. Our substrates power data‑center processors and accelerators today, and that system‑level experience feeds directly into our glass programs with customers seeking even higher bandwidth density and package sizes. The combination of R&D, advanced manufacturing, and customer collaboration allows us to explore glass as an evolution of our existing platform, bringing fine‑line process control, panel experience, and reliability engineering to a new core material.

Our new Competence Center for R&D and IC Substrate Production in Leoben, together with our high-volume sites, provides a path from pilot builds to industrialization as glass matures. Glass core substrates are not a marketing flourish, they are a serious technical answer to the needs of AI/HPC, High Frequency Transmission, and photonics at package scales. AT&S is ready to help customers design, prototype, and scale the glass-based systems that will power the next decade of compute.