Development and Washing Reliability Testing of a Stretchable Circuit on Knit Fabric

Abstract

The smart textiles and wearable technology markets are expanding tirelessly, looking for efficient solutions to create long-lasting products. The research towards novel integration methods and increasing reliability of wearables and electronic textiles (e-textiles) is expanding. One obstacle to be tackled is the washability and the endurance to mechanical stresses in the washing machine. In this article, different layering of thermoplastic polyurethane (TPU) films and knit fabrics are used to integrate three different designs of stretchable copper-based meander tracks with printed circuit boards. The various combinations are washed according to the ISO 6330-2012 standard to analyze their endurance. Results suggest that one meander design withstands more washing cycles and indicate that the well-selected layer compositions increase the reliability. Higher stretchability together with greater durability is accomplished by adding an extra meander-shaped TPU film layer.

Washability of E-Textiles: Failure Modes and Influences on Washing Reliability

“…Similar to the results for the SCB tracks, the torn wires occur at a larger number at the contacting points and the interposer, and to a lesser extent along the length of the tracks [1]. SCB tracks that were washed by Veske et al also exhibit breakages in the tracks, located exclusively at the top and bottom of the meander shapes of the tracks, see Figure 3d [62]. Tao et al register an increase in broken litz wires corresponding to the number of wash cycles.…”

“…Veske et al test SCB type conductive tracks with different meander shapes for their washability. The study reveals notable differences for the different shapes and the protective quality of adding nonfunctional, re-enforcing structures, see Figure 5a [62]. Packaged pairs of LEDs exhibit a better washability in illuminated e-yarns from Hardy et al than LEDs added onto flexible circuit strips.…”

“…of the substrate can impact the washability of textile integrated conductive tracks-according to the specific vulnerabilities of the respective track types. Veske et al achieve better washability with a thicker textile substrate when testing SCB-type conductive tracks [62]. Rotzler et al wash three types of conductive tracks on three different textiles: woven cotton, woven polyester, and knitted polyester.…”

“…Tao et al and Veske et al both achieve better washing results when applying a thicker protective coating [60] or use thicker or double layered TPU foil [62] for their e-textiles. Komolafe finds that, for some applications, increasing encapsulation thickness is not suitable or sufficient for protecting the encased circuits and components.…”

Testing for Wearability and Reliability of TPU Lamination Method in E-Textiles

“…This work focuses on finding the balance between the comfort and reliability of e-textiles. The current research is an extension of a previous study based on laminating a copper-polyimide bus system with different thermoplastic polyurethane (TPU) films and stacks on knit fabrics and conducting reliability (washing) tests on the samples [ 25 ]. This study also focuses on increasing comfort (freedom of movement) by higher stretchability and reliability in thinner TPU stacks by reducing the TPU area.…”