Vertical RF Transition With Mechanical Fit for 3-D Heterogeneous Integration

This paper presents the design, simulation, and measurement of a vertical RF interconnect with mechanical fit for 3-D heterogeneous integration. The mechanical fit is a flip-chip strategy employing interlocking SU-8, an ultra-thick photoresist, structures to prevent misalignment during assembly and increase the reliability of the interconnects. To determine the electromagnetic characteristics, such as insertion loss and the coupling between face-to-face chips, different test structures were fabricated and measured. Experimental results show excellent RF performance up to 110 GHz with low insertion loss (better than 0.1 dB per transition at 40 GHz).