High-CTE Na3P3O9 Ceramic with Excellent Dielectric Properties Significantly Mitigates Thermal Stress of Solder Joints...

Thermal cycling failure of solder joints in surface-mount passive components represents a core bottleneck limiting the reliability of next-generation high-frequency communication systems. Conventional microwave dielectric ceramics exhibit low coefficients of thermal expansion (CTE, 5-12 ppm/°C), causing severe thermal mismatch with commercial SAC305 lead-free solder (21.9 ppm/°C) and copper conductors, which generates enormous thermal stress and induces solder joint cracking during temperature cycling. Herein, we report an intrinsically high-CTE microwave dielectric ceramic Na3P3O9 with a CTE of 22.25 ppm/°C, matching almost perfectly with SAC305 solder. At its optimal sintering temperature of 610 °C, this material simultaneously possesses an ultralow permittivity (εr = 4.88) and ultralow dielectric loss (on the order of 10-4). The physical origins of its excellent comprehensive properties are elucidated via crystal structure analysis and chemical bond theory. Finite element simulations reveal that under the standard electronic packaging thermal cycling condition of -40 to 125 °C, the thermal stress of solder joints on Na3P3O9 is only 54% of that on commercial A6M and 30% of that on conventional alumina. A Ku-band broadband dielectric resonator antenna designed using this material achieves an impedance bandwidth of 3.1 GHz and an in-band total efficiency of >87.2%, fully covering the transmit and receive bands of fixed-satellite and broadcasting satellite services and enabling transmit-receive integration for low Earth orbit satellite terminals. This work provides a high-CTE dielectric material system for addressing the solder joint reliability issue in high-frequency passive components.