Through Silicon Vias Using Liquid Metal Conductors For Reworkable Electronics

Abstract

The design and fabrication of liquid metal interconnects (vias) for reworkable 2.5D device integration is presented in this work. We discuss the implementation of a fully reworkable test module and a partially reworkable module using AL-X as bonding adhesive. The liquid metal under study is eutectic gallium indium (78.6% Gallium, 21.4% Indium) alloy with a melting temperature of approximately 15.7 C. The liquid metal is subsequently used to fill a silicon interposer with 200 m pitch hollow vias. Electrical contact is made to the liquid metal vias through the top and bottom with complementary daisy-chain metallization that provide insight into electrical shorts and opens. This liquid metal interconnect technology can be integrated with existing interposer technologies, including capacitors and traditional (solid metal) through-silicon vias (TSVs) as a via last process. DC and RF simulations are also presented to determine the performance of the liquid metal vias. Preliminary DC measurements under varying temperature were also performed which indicate the lowest operating temperature to be -13.15 C before electrical contact is lost. The highest temperature tested was 80 C with no apparent mechanical failures. The resistance of a transition with two liquid metal vias was determined to be 0.37 miliOhms at room temperature.