Stretchability—The Metric for Stretchable Electrical Interconnects

Stretchable circuit technology, as the name implies, allows an electronic circuit to adapt to its surroundings by elongating when an external force is applied. Based on this, early authors proposed a straightforward metric: stretchability—the percentage length increase the circuit can survive while remaining functional. However, when comparing technologies, this metric is often unreliable as it is heavily design dependent. This paper aims to demonstrate this shortcoming and proposes a series of alternate methods to evaluate the performance of a stretchable interconnect. These methods consider circuit volume, material usage, and the reliability of the technology. This analysis is then expanded to the direct current (DC) resistance measurement performed on these stretchable interconnects. A simple dead reckoning approach is demonstrated to estimate the magnitude of these measurement errors on the final measurement.

Novel Silver-Polymer Blend with High Conductivity and Stretchability for Flexible Interconnects

ABSTRACTStretchable and flexible electronic devices have gained significant attention in recent years, as they can be integrated into many systems such as medical sensors, displays, and robots. One of the primary areas of research is designing stretchable interconnects which provide adequate conductivity and mechanical robustness. Metal-based interconnects have been reported to have the highest conductivity, but are not stretchable enough, while elastomer interconnects are not conductive enough. In this paper we report on a silver polymer blend composite that provides excellent conductivity, stretchability and flexibility for use as a stretchable interconnect. The composite was prepared by dispersing silver flakes in a Polyvinyl alcohol (PVA), Phosphoric acid (H3PO4) and poly(3,4-ethyl-ene-dioxythiophene) (PEDOT):Poly(styrene sulfonic acid) (PSS) polymer mixture. Silver was chosen as it has the highest conductivity of all metals, while the PEDOT:PSS/PVA- H3PO4 blend was chosen as the blend offers a practical trade-off between conductivity and stretchability for the composite matrix. The polymer blend provides conductive pathways between the silver flakes, leading to the blend’s superior electrical properties, even at large deformations. The synthesis process of the composite material, along with the observed electrical and mechanical properties under various straining conditions of the composite will be presented in detail.

In situ observations on deformation behavior and stretching-induced failure of fine pitch stretchable interconnect

Electronic devices capable of performing in extreme mechanical conditions such as stretching, bending, or twisting will improve biomedical and wearable systems. The required capabilities cannot be achieved with conventional building geometries, because of structural rigidity and lack of mechanical stretchability. In this article, a zigzag-patterned structure representing a stretchable interconnect is presented as a promising type of building block. In situ experimental observations on the deformed interconnect are correlated with numerical analysis, providing an understanding of the deformation and failure mechanisms. The experimental results demonstrate that the zigzag-patterned interconnect enables stretchability up to 60% without rupture. This stretchability is accommodated by in-plane rotation of arms and out-of-plane deformation of crests. Numerical analysis shows that the dominating failure cause is interfacial in-plane shear stress. The plastic strain concentration at the arms close to the crests, obtained by numerical simulation, agrees well with the failure location observed in the experiment.