Reliable interfaces for EGaIn multi-layer stretchable circuits and microelectronics.

We tackle two well-known problems in the fabrication of stretchable electronics: interfacing soft circuit wiring with silicon chips and fabrication of multi-layer circuits. We demonstrate techniques that allow integration of embedded flexible printed circuit boards (FPCBs) populated with microelectronics into soft circuits composed of liquid metal (LM) interconnects. These methods utilize vertical interconnect accesses (VIAs) that are produced by filling LM alloy into cavities formed by laser ablation. The introduced technique is versatile, easy to perform, clean-room free, and results in reliable multi-layer stretchable hybrid circuits that can withstand over 80% of strain. We characterize the fabrication parameters of such VIAs and demonstrated several applications, including a stretchable touchpad and pressure detection film, and an all-integrated multi-layer electromyography (EMG) circuit patch with five active layers including acquisition electrodes, on-board processing and Bluetooth communication modules.