RF and mechanical characterization of flip-chip interconnects in CPW circuits with underfill

RF characterization of flip-chip interconnects in coplanar waveguide (CPW) circuits with underfill is reported. The scattering-parameters have been measured up to 40 GHz for GaAs CPW through-line chips flip-chip mounted on an alumina substrate with and without an underfill epoxy. A lumped-element model of flip-chip interconnect has been developed for flip-chip assemblies with and without epoxy. Fatigue life of flip-chip assemblies has been computed for different chip sizes and substrates. The results show feasibility of using underfill encapsulant in microwave/millimeter-wave frequency range.