Electronics in Textiles – Adhesive Bonding Technology for Reliably Embedding Electronic Modules into Textile Circuits

Abstract

The interconnection of electronics and textile circuits is still a main challenge for the fabrication of reliable smart textiles. This paper investigates the thermoplastic adhesive bonding technology. Electronic modules are bonded to textile substrates with a thermoplastic non-conductive adhesive (NCA) film. The modules are placed onto textile circuits with an NCA-film in-between. By applying pressure and heat, the adhesive melts and contact partners touch. Subsequently cooling solidifies the NCA resulting in an electrical and mechanical contact of the electronic module and the textile circuit. This paper shows the suitability of this technology for knitted, woven, non-woven and embroidered fabrics with metal coated yarns as well as with litz-wires as conductors. Besides, it shows that the interconnection process works well with thermoplastically insulated conductors. In addition, the design of interposers has been improved in respect to contact formation and miniaturization compared to previous publications. The pitch of the contact pads is set to 1.27 mm. A textile display was realized with smart RGB-Pixels, which are controlled by an I²C-bus on a quadrupolic woven substrate. It demonstrates the applicability and the potential of this technology.

Analysis of Hot Bar Soldering, Insulation Displacement Connections (IDC), and Anisotropic Conductive Adhesives (ACA), for the Automated Production of Smart Textiles

“…In the following, they used harsher reliability test conditions and more detailed investigations of non-conductive adhesives to confirm the advancement of this technology [16]. Krshiwoblozki et al [17] used mechanical reinforced litz wires with and without insulation. They showed the interconnection to woven highly conductive metal-coated polymer yarns.…”

“…They showed the interconnection to woven highly conductive metal-coated polymer yarns. In addition, the selection and investigation of a suitable thermoplastic insulation material was investigated [17]. Hence, the total potential of adhesive bonding methods has not yet been fully realized [18].…”

“…All contacts could be made in a short time. (a) Picture of a hot bar soldering system with a 3D thermode and two contact points [17]. (b) Temperature profile of a thermode soldering process with a two-phase process; first step: heating and holding to activate the flux, second step: melting the solder and cooling down.…”

Cyber–Physiochemical Interfaces

“…Structural design is a promising way to achieve stretchable FHE integration at system level, which not only enhances the stretchability of soft components, but also bestows stretchability to rigid components. Classical structural design strategies such as wave, [20,82,89,[274][275][276] island-bridge, [37,[277][278][279][280][281] origami/ kirigami, [282][283][284][285][286] and textile [287][288][289][290] have been developed for realizing stretchable systems or modules, which are discussed as follows.…”

“…[290] In addition to energy harvesters, a myriad of wearable/stretchable electronics based on this design have been reported to realize various functionalities, such as logic multiplexers, light-emitting diodes, driving ICs, supercapacitors, and sensors. [287,288,[302][303][304]…”