Polymer-free all-glass millimeter-Wave antenna-in-package platform with vertical-transition-free aperture-coupled feeding at 28 GHz

This paper presents a glass-based antenna-in-package (AiP) platform for millimeter-wave (mmWave) integration and evaluates the platform through thermo-mechanical characterization, routing-loss test coupons, and a 28 GHz antenna demonstration. The platform is intentionally implemented as an all-glass stack rather than a glass-polymer hybrid because thermo-mechanical instability and cracking can arise in multilayer assemblies when constituent materials exhibit large coefficient of thermal expansion (CTE) mismatch. Polymers commonly used in packaging and redistribution structures exhibit thermal expansion rates of tens to hundreds of ppm/ \(^∘\) C, which is substantially higher than that of glass. Therefore, hybrid stacks can be more susceptible to thermal deformation and interfacial stress accumulation due to temperature changes. The proposed platform uses only glass layers to mitigate the CTE mismatch-driven deformation typical of hybrid stacks. In addition, a manufacturing-oriented through-glass via (TGV) formation and filling sequence is introduced to reduce seam-void tendency by controlling the plating boundary condition and encouraging directional copper growth. An aperture-coupled architecture with bottom layer routing is adopted so that feeding can be realized without dedicated via-fed radiator transitions. Radio-frequency (RF) viability is quantified through transmission line coupons and confirmed by measured reflection coefficient and radiation results from an aperture-coupled patch element and a 4 \(×\) 1 array at 28 GHz. The combined results demonstrate the structural and RF feasibility of the proposed glass-based platform for millimeter-wave AiP integration with reduced thermo-mechanical mismatch risk and low routing loss.