The Effect of Encapsulation Geometry on the Performance of Stretchable Interconnects.

The stretchability of electronic devices is typically obtained by tailoring the stretchable interconnects that link the functional units together. The durability of the interconnects against environmental conditions, such as deformation and chemicals, is therefore important to take into account. Different approaches, including encapsulation, are commonly used to improve the endurance of stretchable interconnects. In this paper, the geometry of encapsulation layer is initially investigated using finite element analysis. Then, the stretchable interconnects with a narrow-to-wide layout are screen-printed using silver flake ink as a conductor on a thermoplastic polyurethane (TPU) substrate. Printed ultraviolet (UV)-curable screen-printed dielectric ink and heat-laminated TPU film are used for the encapsulation of the samples. The electromechanical tests reveal a noticeable improvement in performance of encapsulated samples compared to non-protected counterparts in the case of TPU encapsulation. The improvement is even greater with partial coverage of the encapsulation layer. A device with a modified encapsulation layer can survive for 10,000 repetitive cycles at 20% strain, while maintaining the electrical and mechanical performance.