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

Mahmoud Mosallaei,Matti Mäntysalo,Jarno Jokinen,Mikko Kanerva

doi:10.3390/mi9120645

Abstract

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.

Highlights

Stretchable electronics have attracted a large amount of attention in the last few years, since they can bring freedom of design in a variety of applications [1]
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The samples with encapsulation layers showed considerable improvement in a single tensile test when compared to the non‐encapsulated samples

Summary

Introduction

Stretchable electronics have attracted a large amount of attention in the last few years, since they can bring freedom of design in a variety of applications [1]. One common method for making a stretchable device is to use the island-bridge technique, because of its ability for large and reversible stretchability [8] In this approach, functional units are miniaturized while they are still rigid. The major issue is that metals in bulk form are not especially flexible and stretchable, due to their high Young’s modulus and very low stretchability (

Materials

Fabrication

FE Analysis

Findings

The Peel Test