Performance characteristics of thin film multilayer interconnnects in the 1-10 GHz frequency range

Multichip packaging approaches that provide short chip-to-chip interconnects are required to utilize fully the high-speed potential of silicon ECL (emitter-coupled logic) and GaAs ICs. To maintain signal fidelity at gigahertz clock speeds, interconnects must be designed as impedance-controlled transmission lines with proper concern for discontinuities, crosstalk, and attenuation. At present, there is very little quantitative data for frequencies greater than 1 GHz on the effect of the typical elements encountered in hybrid and multichip packaging. Initial results from a program to develop much of this data are presented. The platform chosen to quantify high-frequency multichip packaging effects is a copper/polyimide-based thin-film multilayer (TFML) technology. Measurements of return loss, insertion loss, and characteristic impedance of interconnects of various lengths were made up to 9.045 GHz. Signal attenuation and crosstalk of 1- and 2-GHz digital signals were measured and simulated. In general, the loss and crosstalk values obtained were low enough to permit the transmission of gigahertz digital signals over typical interconnect lengths encountered in a multichip module.