Biphasic liquid metal composites as soldering systems for robust soft-rigid interfacing in stretchable hybrid electronics.

Stretchable hybrid electronics are integral in numerous domains such as healthcare, soft robotics, and human-machine interfaces. However, their development encounters significant challenges under mechanical deformation, primarily due to stress concentration at soft-rigid interfaces. Structural engineering or rigid-filler composites, as conventional soldering solutions, face critical limitations including restricted strain tolerance and inherent trade-offs between conductivity and stretchability. Intriguingly, liquid metals (LMs) can offer fluidic conductivity and extreme stretchability. By further hybridizing with polymers or particulates, biphasic LM composites have emerged as advanced soldering systems to realize robust soft-rigid connections, thus moving toward fabrication of reliable stretchable hybrid electronics. This article reviews recent biphasic LM composites serving as soldering systems for hybrid electronic integration. Key design considerations in fabrication of competent solders are firstly discussed. Next, various material combinations in the biphasic LM composites, as well as methods used to connect and weld dissimilar functional components, are discussed. Finally, the current challenges and future perspectives of these LM-based soldering systems are proposed.