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For biomedical and textile applications, the comfort of the user will be enhanced if the electronic circuits are not only flexible but also elastic. This letter reveals a simple mouldedinterconnect-device technology for the construction of elastic point-to-point interconnections, based on 2-D spring-shaped metallic tracks, which are embedded in a highly elastic silicone film. Metal interconnections of 3-cm long were constructed with an initial resistance of about 3 Ω, which did not significantly increase (< 5%) when stretched. A stretchability above 100% in one direction has been demonstrated.

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The deformation behavior and failure mechanisms of parallel-aligned, horseshoe-patterned, stretchable conductors encapsulated in a polymer substrate were investigated by numerical and experimental analyses. A design guideline for the optimal pitch between the conductors was proposed through numerical analysis, and two extreme cases-fine and coarse pitches-were investigated by in situ experimental observations. The experimental results demonstrate that the stretchable conductors enable elongation up to 123 and 135% without metal rupture for the fine and coarse pitches, respectively. The difference between these numbers is much smaller (12%) than expected from the simulations. It is found and confirmed by a modified simulation model that the reason for this is interfacial delamination, the onset of which depends on the pitch of the conductors and occurs before metal rupture of the conductors. The definition of 'stretchability of the electronic interconnects' is discussed based on the facts that two different failure mechanisms occur: interfacial delamination and metal rupture.

Abstract. Stretchable electronics offer increased design freedom of electronic products. Typically, small rigid semiconductor islands are interconnected with thin metal conductor lines on top of, or encapsulated in, a highly compliant substrate, such as a rubber material. A key requirement is large stretchability, i.e. the ability to withstand large deformations during usage without any loss of functionality. Stretching induced delamination is one of the major failure modes that determines the amount of stretchability that can be achieved for a given interconnect design. During peel testing, performed to characterize the interface behaviour, the rubber is severely lifted at the delamination front while at the same time fibrillation of the rubber at the peel front is observed by ESEM analyses. The interface properties are established by combining the results of numerical simulations and peeling experiments at two distinct scales: the global force-displacement curves and local rubber lift geometries. The thus quantified parameters are used to predict the delamination behaviour of zigzag and horseshoe patterned interconnect structures. The accuracy of these finite element simulations is assessed by a comparison of the calculated evolution of the shape of the interconnect structures and the fibrillation areas during stretching with experimental results obtained by detailed in-situ analyses.

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.