Characterization and lumped circuit model of ultra-wideband flip-chip transitions (Dc - 110 GHz) for wafer-scale packaging

An ultra-wideband flip-chip transition is proposed for wafer level packaging applications. The locally matched flip-chip scheme has an air cavity underneath a flip-chip die and local trenches in the flip-chip bond pad area to provide matching. The measured response up to 110 GHz has a return loss below 20 dB across 96% of the band and has an insertion loss improvement of 2.2 dB at 110 GHz. The design approach is simple and requires no additional space. Also presented is lumped element circuit model for the transition region of conventional and locally matched flip-chip interconnect.