Millimeter-wave coplanar strip (CPS) line flip chip packaging on PCBs

In this paper, we studied coplanar strip (CPS) transmission lines on PCBs in millimeter-wave in terms of attenuation constant with different configurations. The purpose for CPS lines is to facilitate flip-chip packaging of future MMIC chips on the PCBs. Attenuation constant is 0.8dB/cm at 30GHz on RT/Duroid 6010. We analyzed the attenuation coefficient of CPS lines based on geometrical configuration to achieve an optimum design on PCBs. An application of coplanar strip transmission lines in microwave flip-chip configurations implemented with solder bumps is presented. We have shown that return loss, S₁₁ (dB) is higher than 20 dB up to 50 GHz for the flip-chip configuration using coplanar strip lines. To improve performance further, the solder bumps have to be designed as an integral part of the transmission line. The attenuation coefficient of different types of transmission lines with 50 Ohm characteristic impedance, such as microstrip lines, and coplanar strip lines on the PCBs, were calculated up to 50 GHz and compared. In order to have low attenuation constant using CPS lines, not only are design parameters such as dielectric constant, electrodes´ widths for signal and ground lines important, effect of backside metallization also has to be understood. Also we present a new method to reach optimum design through the analysis of flip chip interconnection.