Strain Isolation for Flexible-to-Stretchable Electrical Interconnects

The interface between flexible and stretchable electronics is a critical junction to enable stretchable sensors and systems. The key barrier is integrating soft material together with higher modulus substrates, where strain at the interface causes electromechanical failure. We report a flexible-to-stretchable interconnect between thermoplastic polyurethane and a flexible polyimide PCB, using a stretchable liquid-metal conductive ink. A method of strain isolation at this critical junction allows for strains above 200% along the trace length while maintaining electrical continuity between material. Digital image correlation is used to monitor localized strain around the interconnect, demonstrating a 62.5% reduction in stretch of the soft material within the strain-isolated zone. The electrical interconnect remains functional up to the point of mechanical failure of the substrate at 280% strain.