Optimised Hot-Via Transition with 20 dB Return Loss for MMIC Packaging from DC to 110 GHz

A hot-via transition from a monolithic microwave integrated circuit (MMIC) to a printed circuit board (PCB) has been developed with a measured back-to-back insertion loss less than 0.88 dB and return loss higher than 20 dB from dc to 110 GHz. Two techniques are proposed to extend the maximum operating frequency of the microstrip to grounded coplanar waveguide (GCPW) transition. An oversized microstrip line is used on the MMIC to increase capacitance, and a critical return path via in the PCB is positioned near the edge of the hot-via gap to lower inductance. Both techniques improve the maximum operating frequency to 110 GHz for a transition with return loss better than 20 dB and insertion loss of 0.39 dB. To the authors' best knowledge, this MMIC packaging technique demonstrates the highest bandwidth achieved for a dc connected hot-via transition with less than 1 dB back-to-back insertion loss.

I. Introduction

The performance of integrated circuits at millimetre-wave frequencies such as E-band (60–90 GHz) and W-band (75–110 GHz) can be severely impacted by the quality of the interconnect between the die and its package environment. There are many important considerations required in the design of microwave interconnects. Primary design goals are minimisation of insertion loss and impedance mismatch. Insertion loss between an amplifier and antenna impacts directly on system performance metrics. For example, increased bit-error-rates in communication links and reduced dynamic range in radar applications. Impedance mismatch presented to the MMIC results in unwanted load-pull effects on active devices that deteriorate power, linearity and noise figure. Other goals include robustness to manufacturing tolerances, long-term reliability and reduced manufacturing costs.