Design and Analysis of a Multi-Stage LTCC Transition for GaN Flip-Chip Interconnect to SMA Edge Launch in C-Band SiP

This paper presents a multi-stage, low-loss transition for routing GaN flip-chip signals to an SMA edgelaunch connector, realized using Low Temperature Co-Fired Ceramic (LTCC) technology for System-in-Package (SiP) integration. Built on a five-layer LTCC substrate, the design manages a 389 μ m flip-chip pad pitch and utilizes varied tape thicknesses to optimize vertical routing and a constant 50 Ohm impedance. The three-section interconnect comprises a BGA-tomicrostrip (MS) connection, a vertical MS transition, and a MS-to-SMA interface. Although optimized for the C-band (5 to 6 GHz), the design achieves exceptional broadband performance. Simulation confirms an insertion loss of less than 0.4 dB across the entire DC to 10 GHz bandwidth. Within the target 5 to 6 GHz range, insertion loss is better than 0.25 dB and return loss is better than 20 dB. This LTCC solution offers an efficient, high-density, minimal-loss route for high-speed GaN signals.