Mechanically driven strategies to improve electromechanical behaviour of printed stretchable electronic systems

Abstract

Stretchable electronics promise to extend the application range of conventional electronics by enabling them to keep their electrical functionalities under system deformation. Within this framework, development of printable silver-polymer composite inks is making possible to realize several of the expected applications for stretchable electronics, which range from seamless sensors for human body measurement (e.g. health patches) to conformable injection moulded structural electronics. However, small rigid electric components are often incorporated in these devices to ensure functionality. Under mechanical loading, these rigid elements cause strain concentrations and a general deterioration of the system’s electrical performance. This work focuses on different strategies to improve electromechanical performance by investigating the deformation behaviour of soft electronic systems comprising rigid devices through Finite Element analyses. Based on the deformation behaviour of a simple stretchable device under tensile loading, three general strategies were proposed: local component encapsulation, direct component shielding, and strain dispersion. The FE behaviour achieved using these strategies was then compared with the experimental results obtained for each design, highlighting the reasons for their different resistance build-up. Furthermore, crack formation in the conductive tracks was analysed under loading to highlight its link with the evolution of the system electrical performance.

Fully Integrated Wireless Elastic Wearable Systems for Health Monitoring Applications

“…The FE results are in agreement with the cracking pattern found in the tested samples, as shown in Fig. 6(c), where it is possible to see that higher cracking density is achieved in the conductive track regions right next to the regions covered by the encapsulant, as was also noted and analyzed for simpler geometries in previous publications [16], [17]. While the encapsulant protects from surface cracking under tensile deformation, in fact, it also promotes the formation of stiffer regions, which in turn strongly influence the overall deformation behavior under tensile load.…”

“…For this reason, the FE model closely mimicked the structure of the sample under deformation and featured all the 43 rigid components present in the real device, together with the encapsulant, the substrate and the conductive ink. The mechanical response chosen for the last two can be found in the previous works [16], [17], while the encapsulant was assumed to behave as a linear elastic material with a Young's modulus equal to 49 MPa. The bonding between the different components was assumed to be ideal without possible delamination and the loading conditions imitated the ones imposed by the tensile tester during 10% of tensile deformation imposed.…”

“…Combined experimental and in silico approaches were utilized to localize the failure points during cyclic strain. Finite Element modeling (FEM) proved to be an useful technique to analyze and predict the mechanical deformations of surface-mounted components on simple stretchable devices [16], [17]. Particularly in this study, FE analyses were used in combination with the experimental electromechanical reliability tests to spot the potential failure points that are not easily accessible for visual inspection or electrical testing due to the supporting (encapsulation) layers.…”

Screen-Printing of Conductive Nanomaterial Inks for Stretchable Electronics

“…In order to reduce strain concentration, especially when complex devices are in question, arrangement of the components must be optimized. To limit the straining effect in the vicinity of rigid islands shielding frames are usually introduced [5]. These shielding frames are introduced in order to reduce strain concentrations near vulnerable regions of the substrate.…”

“…Stretchable electronic devices often include surfacemounted devices (SMDs). SMDs, such as rigid passive components, integrated circuits, batteries, connectors, etc., form rigid islands [5] that tend to affect electromechanical behavior of the device. Strain concentration in the vicinity of these rigid areas usually leads to fracture of conductive paths and consequentially to device failure.…”