Liquid metal vertical interconnects for RF flip-chip assembly

This paper describes a new process for using room temperature liquid metals as the interconnect material for flip chip bonding. The proposed liquid metal interconnects are not susceptible to damage caused by thermo-mechanical stress and are therefore an attractive alternative to solid phase solder bumps. A new interconnect structure is presented involving a patterned underfill dielectric material to contain the liquid metal on the bottom carrier, and electroplated pins on the top chip to mate with the socket and make contact with the liquid metal. RF and DC measurements were performed on the liquid metal transition showing an insertion loss of <0.5dB up to 20 GHz.