Glass Core Substrates for High-Density Chiplet Integration

The increasing performance demands of AI computing systems, particularly those leveraging chiplet based architectures, necessitate advanced substrate technologies capable of supporting high bandwidth, compact form factors, and efficient power delivery. A critical enabler in this context is the substrate's ability to maintain high interconnect density with minimal signal loss and mechanical distortion. Conventional organic core substrates, while mature and widely adopted, encounter fundamental limitations when scaling to fine-pitch interconnects with structure widths in the single-digit micrometer range. These constraints hinder their suitability for next-generation chiplet systems requiring seamless inter-die connectivity and ultra-low-loss signal transmission. Glass core substrates present a compelling alternative, offering superior dimensional stability, low dielectric loss, and the potential for multiple sub-micrometer redistribution layers. This presentation outlines the process flow for fabricating glass core substrates, emphasizing key steps such as via formation, metallization, and RDL formation. A comparative study will be presented to delineate the threshold at which organic substrates become geometrically and electrically inadequate, necessitating a transition to glass. Activities and results from the Glass Panel Technology Group (GPTG), coordinated by Fraunhofer IZM, are discussed, including preliminary reliability testing and comparative studies on the geometrical stability of glass versus organic substrate cores.