EGaIn–Metal Interfacing for Liquid Metal Circuitry and Microelectronics Integration

Abstract Eutectic gallium–indium (EGaIn) has attracted significant attention in recent years for its use in soft and stretchable electronics. However, advances in scalable fabrication approaches and effective electromechanical interfaces between liquid metal (LM) traces and microelectronics are still needed to create functional soft and stretchable electronics. In this study, EGaIn–metal interfacing for the effective integration of surface‐mount microelectronics with LM interconnects is investigated. The electrical interconnects are produced by creating copper patterns on a soft‐elastomer substrate, and subsequently exposing the substrate to EGaIn, which selectively wets the Cu traces. To create strong electromechanical connection between EGaIn and microelectronics, the terminals of the LM‐coated traces are “soldered” to the metal pins of the packaged microelectronic circuits using a novel HCl‐vapor treatment. In combination, the fabrication and microelectronics‐interfacing approaches enable creating stretchable circuits composed of LM wiring and packaged microelectronics. It is found that the HCl‐vapor treatment significantly improves electrical conductivity at the LM–pin interface while enhancing the strain limit of the soft circuits and the reproducibility of the interface. The applicability of this approach in creating soft‐matter circuits is demonstrated through two illustrative examples—a circuit with a digital 9‐axis inertial measurement unit and a temperature sensor; and a circuit with a 3‐axis analog accelerometer.