Synergistic enhancement of thermal stability and dielectric performance of BT resin composites via difunctional phthalonitrile monomers for high-frequency PCB substrates

The escalating demands of high-frequency communication necessitate printed circuit boards (PCB) with exceptional thermal stability and dielectric properties. This study introduces a novel strategy by incorporating two distinct phthalonitrile monomers into a bismaleimide-triazine (BT) resin matrix. At low temperatures, aminophthalonitrile initiates the ring-opening of benzoxazine units, generating catalytically active phenolic Mannich bridges. This reaction strategically modulates curing kinetics, resulting in a dielectrically stable, highly crosslinked network. Phthalonitrile-based clad copper laminates (PNCCLs), reinforced with silicon dioxide filler, were subsequently fabricated using a tailored molding process. The effects of post-curing temperature on heat resistance, mechanical properties, and dielectric performance were systematically investigated. The resulting PNCCLs exhibit a low coefficient of thermal expansion (19 ppm from 50 to 300 °C) and a glass transition temperature exceeding 300 °C. Crucially, the laminates demonstrate exceptional dielectric stability, and the dielectric constant (ε) and loss (tanδ) remain remarkably stable at 3.6 and 0.008 (10 GHz), respectively, across a wide operating temperature range from −50 to 150 °C. Extended into the terahertz regime, ε and tanδ values reach 2.6 and 0.15 at 3 THz. Detailed analysis correlates these frequency-dependent behaviors with molecular polarity and backbone rigidity, elucidating the dominant loss mechanisms in the THz domain. This integrated resin design and processing approach provides a scalable pathway for next-generation, high-performance PCBs for advanced communication systems.