Glass in Electronic Packaging and Integration: High Q Inductances for 2.35 GHz Impedance Matching in 0.05 mm Thin Glass Substrates

This work demonstrates 50 μm (2.0 mil) thin SCHOTT glass AF32eco as a RF substrate. Superior electrical performance and miniaturized component or package size in both vertical and lateral dimensions compared to traditional components and two-dimensional (2D) packages are shown to be feasible with the 3D fabrication approach with such thin glass. Vias with a diameter of 50μm are made at SCHOTT using laser structuring. Either sides of the glass substrates are coated with a thin layer of a polymer dielectric. The through-holes are re-opened and metallization processes are performed to simultaneously create a thick copper metallization on both surfaces as well as on the vias to make them conducting. The metallization is structured with semi-additive patterning using photolithography and etching to obtain solenoid inductors for matching networks of filter elements. The magnetic field of the components is mainly parallel to the glass substrate. Inductances with 1.7 nH and 1.9 nH are designed and fabricated using different structures for shielding. The performance metrics of the demonstrated glass-integrated passive devices (IPDs) and modules were characterized. Excellent correlation between modeling and measured results were observed. Characterization of the inductances revealed quality factors (Q-values) of 60 and more at 2.35 GHz. The Q-values of the inductances are confirmed by three independent measurement methods and correspond well to field simulation results. The basic building blocks demonstrated in this paper can lead to a new generation of ultra-thin 3D RF modules with substrate-embedded matching networks and filters, superior performance and lower cost compared to laminate and FO-WLP based approaches.