Flip-chip interconnects for frequencies up to W band

A flip-chip approach for millimetre-wave frequencies up to W band is presented. Key to high return loss at the interconnect is a small bump-pad area. This is accomplished by means of Au-electroplated bumps and thermocompression flip-chip bonding. The electrical characteristics of this mounting technique are verified by measurements on test structures. The frequency range of operation can be further extended by simple compensation structures at the interconnect. A return loss level beyond 20 dB up to 80 GHz is achieved along with excellent reproducibility