Stretching Reliability of SMD Electronics Integrated on Elastic Fabric

This paper presents a manufacturing flow to integrate surface mounted device (SMDs) on elastic fabric. In this concept, manufacturing processes are based on printing, converting and assembly to integrate rigid SMD electronics with high-performance functionality on a stretchable substrate, and hot laminating this entity on an elastic fabric. The presented manufacturing flow exploits novel material solutions like stretchable inks and adhesive bonding technology to achieve needed electro-mechanical performance at low processing temperatures. The study includes reliability assessment for test samples under mechanical loadings. The test structures comprise 0402” sized SMD thermistors and printed wiring with multiple material and design configurations integrated on both thermoplastic polyurethane (TPU) substrate and elastic fabric by means of TPU lamination. Test coverage for prepared samples encompasses maximum stretching test, cyclic stretching, and cyclic stretching with rotation, thus enabling extensive reliability assessment for various sample configurations under interest. The results show mainly over 100% stretchability without catastrophic failure for textile integrated SMD samples in maximum stretching tests. In cyclic tests covering 25% elongation with and without ±90° rotation, durability of SMD-based structures is limited in comparison to baseline samples without component integration. The conducted tests and electro-mechanical characterization pinpoint the importance of material stack strength and layout design. Narrow TPU cut for integrating SMD electronics on textile has lower effect on mechanical behavior under stretching. This reflects also on electrical performance and reliability.