Vertical RF Transition with Mechanical Fit for Three-Dimensional Heterogeneous Integration

This paper presents the design, simulation and measurement of a vertical interconnect with mechanical fit for three-dimensional heterogeneous integration. The mechanical fit is a strategy employing interlocking SU-8 structures to transition between flip-chip style stacked chips through vertical CPW transmission lines. The mechanical fit is introduced in this paper to reduce flip-chip alignment difficulty and increase the reliability of the interconnects. This paper also describes a process for using pre-fabricated active ICs in a mechanical fit vertical configuration. Experimental results show excellent RF performance up to 50 GHz, with extremely low insertion loss (better than 0.25 dB at 40 GHz per transition). The transitions have been fabricated and tested for 380 m-thick silicon substrates with passive components and experiments are being conducted on active components.