Broadband characterization of 6G microelectronics packaging materials: EN-A1 alkali-free boroaluminasilicate glass substrates

With the commercial deployment of 5G and 6G wireless communication networks, high-frequency packaging is crucial to the stringent performance requirements of THz wireless components and integrated circuits (ICs). To date, owing to the high stability in service and manufacturing, tailorable coefficients of thermal expansion (CTE) matching to Si (3.8×10^-6/K versus 3.3×10^-6/K), as well as excellent scalability, glasses have attracted significant attention as a promising substrate material for packaging future-generation network systems. In this work, EN-A1 alkali-free boroaluminasilicate glass, a novel 6G microelectronic packaging material from Asahi Glass Corporation, is characterized by terahertz (THz) time-domain spectroscopy. A Fabry Pérot cancellation procedure and 5th-order polynomial curving fitting [1,2], are implemented prior to dielectric-parameter extraction to suppress oscillations that otherwise appear at frequencies ν<0.9 THz and smooth out fluctuations from noise. Frequency-dependent dielectric properties [refractive index n(ν), absorption coefficient α(ν), permittivity ε^′, and loss tangent tanδ(ν)] of EN-A1 glass are obtained from 200 GHz to 2.5 THz. We find that the value of the refractive index n(ν) decreases slightly from 2.466 at 200 GHz to 2.2 at 2.5 THz, the value of the absorption coefficient α(ν) increases dramatically from 5.68 cm^-1 at 200 GHz to 115.6 cm^-1 at 2.5 THz, the value of the permittivity ε^′ decreases from 6 at 200 GHz to 4.82 at 2.5 THz, and the value of the loss tangent tanδ increases from 0.048 at 200 GHz to 0.093 at 2.5 THz, respectively. Although dielectric characterization was carried out on ABF/EN-A1 glass/ABF stackups from 20 to 170 GHz in Ref. [3], we extend the work there by providing the first broadband material characterization of bare EN-A1 glass substrate from 200 GHz to 2.5 THz.