Coaxial transitions for CPW-to-CPW flip chip interconnects

A novel coaxial transition for CPW-to-CPW flip chip interconnect is presented and experimentally demonstrated. To realise the coaxial transition on the CPW circuit, benzocyclobutene was used as the interlayer dielectric between the vertical coaxial transition and the CPW circuit. The coaxial interconnect structure was successfully fabricated and RF characterised to 67GHz. The structure showed excellent interconnect performance from DC up to 55GHz with low return loss below 20dB and low insertion loss less than 0.5dB even when the underfill was applied to the structure.