High-Performance Millimeter-Wave SOP Technology with Flip-Chip Interconnection

In this paper, we demonstrate the development of the system-on-package (SOP) technology using the SNU´s deposited multi-chip module (MCM-D) technology for compact and high-performance millimeter-wave (mm-wave) modules. A distinctive feature of our MCM-D technology is the existence of Si-bumps and ground-bumps. The Si-bumps having a low coefficient of thermal expansion (CTE) and a high thermal conductivity can solve thermal and thermo-mechanical problems of the flip-chip structure. And the ground-bumps can make easy ground connection without deep-via process. From thermal analysis using a three-dimensional (3-D) finite element method (FEM) simulator, we confirmed that the proposed substrate has the significantly improved thermal performance. And the integrated passives such as the SiN_x capacitor, the NiCr resistor, and the broadside Lange coupler were fabricated and characterized for SOP technology. Especially port terminator was optimized to provide a good match so that the reflection of microwave power is minimized. The flip-chip transition between the thin-film microstrip (TFMS) line and the coplanar waveguide (CPW) line on the flipped chip is also optimized for mm-wave range. As an illustration of this implementation methodology, a W-band transmitter was realized on the SNU´s MCM-D substrate by means of the flip-chip technology. And the MCM-D substrate was fabricated for a mm-wave power amplifier (PA) module.