Novel Ba6Mg(11+x)F(34+2x) binary fluoride ceramics with excellent microwave/millimeter-wave dielectric properties for high-reliability packaging applications

Fluorides are promising low-permittivity microwave dielectric ceramics with exceptional dielectric properties. However, achieving optimal densification remains a challenge for most unary fluoride ceramics, and systematic studies on binary or polyfluoride ceramics are limited. In this study, novel non-stoichiometric Ba₆Mg_(11+x)F_(34+2x) (x = 0–0.5) binary fluoride ceramics were successfully prepared using the solid-state reaction method. The non-stoichiometric binary composition design enhanced the sintering behavior and effectively suppressed the formation of secondary phases, resulting in outstanding microwave dielectric properties. The optimal performance was achieved at x = 0.25 when sintered at 825°C, with ε_r = 8.2 ± 0.03, Qf = 77,700 ± 1100 GHz at 24 GHz, and τ_f = –83.95 ± 1.4 ppm/°C. Additionally, Ba₆Mg_(11+x)F_(34+2x) ceramics exhibited a reduced contact angle compared to unary fluorides and showed an excellent match in thermal expansion coefficient (17.6 ppm/°C) with copper electrodes, making them highly suitable for addressing thermal stress issues in integrated circuit packaging.