Study on Reduction of Local Transmission Loss Caused by Glass Cloth in High-Frequency Substrates

Recently, data centers have faced a major challenge due to the rapid growth of data volume. In particular, high-speed signal processing is essential in network switches, underscoring the critical need to develop substrate materials suitable for next-generation high-frequency applications. Although it has long been recognized that glass cloth within substrates can introduce additional transmission losses, a further issue has recently been identified: a localized transmission loss (dip) and its higher-order dips. In this paper, we demonstrate that this phenomenon also occurs in the latest high-frequency substrates. Through theoretical calculations, electromagnetic field simulations, and experimental measurements, we clarify the mechanism responsible for dip formation, propose methods for its suppression, and suggest strategies to prevent the phenomenon entirely.