Mechanical Fatigue in Liquid-Metal Interconnects: Failure Mechanism Analysis and Validation of Improvement Strategies

Abstract

Stretchable electronics that combine mechanical compliance with reliable electrical performance are essential for applications in soft robotics, wearable systems, and healthcare monitoring. Among the available conductive materials, liquid metals (LMs) offer exceptional conductivity and intrinsic deformability when encapsulated in elastomers, yet the long-term reliability remains a challenge. This work addresses the critical issue of robust interconnections between the LM and rigid or flexible components, where stress concentration leads to failure under repeated strain. Herein, the robustness of such interfaces is improved by first eliminating secondary failure modes, such as silicone rupture and short circuits, until connection failure is the final dominant mode. Targeted connector designs are introduced to improve connection stability. Through X-Ray tomography, delamination between encapsulant and connector is identified as the primary failure mechanism, which is subsequently mitigated through material based strain relief around the LM-solid interface. Devices incorporating this strategy withstand at least one million cycles at 50% strain, even when rigid components are integrated. Further, at 100% strain, the cyclic durability increases from 16% survival rate to 50% survival rate after 100 000 stretch cycles by applying strain relief. These findings establish a framework for reliable LM-based stretchable interconnections in demanding applications.