Design of Coaxial TGV Substrates; Enhancing RF Via to Via Isolation

Abstract

Enhanced electronic substrate design objectives for higher frequency products (5G telecom systems) can now be achieved with the use of novel coaxial-thru-via configurations in glass (TGVs). When compared with standard pillar filled thru-vias in glass, coaxial-thru-vias exhibit greater than 40dB improvement in via-to-via crosstalk isolation and 0.5dB improvement in insertion loss both at 30 GHz. Coaxial-Thru-Vias provide precise unadjusted 50 Ohm impedance matching device designs at the 5G product frequencies. The coaxial dielectric core chemistry is modifiable to tune electrical parameters to meet specific design requirements. This paper summarizes all designs, simulations, and modeling performed to date. The superior properties of coaxial vias in glass and fused silica over standard pillar vias are documented and captured in sweeps to 100 GHz. Via and pitch dimensions of 100/200 and 50/100 um have been assessed. Manufacturing methods have been demonstrated using thick film conductor materials in prototype designs. Coaxial vias can optionally be fabricated as dual-purpose configurations reducing thru-via count requirements, substrate footprints, and package/module costs.