Ultra wide-band, low Loss RF substrate with high-density DC routing supporting 5G/6G flip-chip RFICs

This paper presents the development of a substrate/interposer technology that is capable of supporting DC signal line routing down to <1mil trace and space densities, but also supports wideband, high-frequency and industry leading low loss RF routing from to beyond 175GHz. Building off of the proven performance and reliability of the PolyStrata® technology enabled air-coax routing, this paper discusses the development and addition of a redistribution technology that enables multilayer, high density DC signal routing at any point during the PolyStrata® process. This enhances the Polystrata® offering to a truly integrated substrate manufacturing process supporting high density interconnect requirement of flip-chip RF ICs as well as low loss high performance RF routing. The paper describes the design and fabrication of a demonstration part designed to accept a D-Band Flip-Chip RFIC. The chip side interconnects are 50um diameter copper pillar with solder cap, at 100um pitch with over 200 interconnects on a die. Multiple connections were required from 10Ghz to 175GHz as well has 30+ DC signal lines. The design can support this level of interconnect density and act as an interposer for next level interconnect to a printed circuit board. DC lines were routed out to a 400um pitch while RF interconnects can support transitions to micro-strip or strip-line PCB routing technology or waveguide, for easy and low loss interconnect to the next level system. An added benefit of being integrated into the PolyStrata® process is that high-performance passive components can be monolithically integrated into the interposer, and the demonstration vehicle implements a mmWave pass-band filter as well.