For the improvement of the performance and function of electronic textiles (e-textiles), methods for electronic component mounting of textile circuits with electrical and mechanical durability are necessary. This manuscript presents a component mounting method for durable e-textiles, with a simpler implementation and increased compatibility with conventional electronics manufacturing processes. In this process, conductive patterns are directly formed on a textile by the printing of conductive ink with deep permeation and, then, components are directly soldered on the patterns. The stiffness of patterns is enhanced by the deep permeation, and the enhancement prevents electrical and mechanical breakages due to the stress concentration between the pattern and solder. This allows components to be directly mounting on textile circuits with electrical and mechanical durability. In this study, a chip resistor was soldered on printed patterns with different permeation depths, and the durability of the samples were evaluated by measuring the variation in resistance based on cyclic tensile tests and shear tests. The experiments confirmed that the durability was improved by the deep permeation, and that the samples with solder and deep permeation exhibited superior durability as compared with the samples based on commercially available elastic conductive adhesives for component mounting. In addition, a radio circuit was fabricated on a textile to demonstrate that various types of components can be mounted based on the proposed methods.

Serpentine interconnects are promising for electronic textiles (e-textiles), because they can maintain low electrical resistance even under cyclic large deformation. However, previous studies have not deeply discussed their failure lifetime, and the relationship between the elongation (engineering strain applied to entire structure) and cycle number to failure remains unclear. This clarification will contribute to the lifetime prediction. Therefore, this study investigates the relationship using interconnects having the same conductive material and geometric parameters but with different laminated structures: copper adhered to a polyurethane laminated knit textile (type A); copper adhered directly to a knit textile (type B); and polyethylene-naphthalate-laminated copper adhered to a knit textile only at both ends of the interconnect (type C). An elongation of 7%–70% was applied to the prepared samples with a tensile testing machine. The measurement and analytical calculation show that the type-C interconnects have the highest lifetime, and the relationship between the elongation ϵ appl and cycle number to failure N f is given by ϵ appl = A′N f −c/2, where A′ is the coefficient determined by the material properties, geometric parameters, and laminated structures, and c is the fatigue ductility exponent of copper. Moreover, this paper demonstrates the washing durability of an e-textile device using type-C interconnects. A cloth-face-mask-type device that monitors facial skin temperatures was fabricated and repeatedly washed with a washing machine. The demonstration confirms that the temperature variations were stably monitored before and after the first washing, and the multiple failures occurred in the interconnects after ninth washing.

We propose a self-healing metal wire using electric field trapping of gold nanoparticles by a dielectrophoresis force. A cracked gold wire can retrieve its conductivity through the self-healing function. In this paper, we examine the healing voltage causing the electric field trapping and determine the healing time, which is relevant to future device applications. First, the forces acting on a nanoparticle are analyzed and a theoretical healing voltage curve is calculated. Then, gold wires with 200-to 1,600-nm-wide cracks are fabricated on glass substrate and the self-healing function is verified through healing experiments. As a result, gold wires with cracks of up to 1,200 nm in width are successfully healed by applying less than >2.5 V (on average), and the experimental results correspond almost exactly with the calculated healing voltage curve. The average healing times are 10 to 285 s for 200-to 1,200-nm-wide cracks. Through scanning electron microscope analysis after the healing experiments, we confirm that the cracks are healed by assembled nanoparticles.

Stretchable thermoelectric generators (S-TEGs) have the potential to utilize waste heat from sources with complex and dynamic surfaces. However, their thermoelectric performances are still lower than those of conventional hard and rigid TEGs and are easily degraded by large or cyclic deformations due to electrical failure. An approach that improves both stretchability and thermoelectric performance is required. This study presents and explores the improvements enabled by an ultrasoft silicone sponge encapsulation for S-TEGs using silicone-encapsulated serpentine interconnects for the internal electrical wiring of the bismuth-telluride-based thermoelectric elements. The ultrasoft silicone sponge is characterized by a low Young’s modulus (0.01 MPa) and low thermal conductivity (0.08 W m−1 K−1) owing to its open-cell structure. We consider that the low Young’s modulus decreases the internal stress in the interconnects under deformation and that the low thermal conductivity increases the temperature differences in the thermoelectric elements under constant heat flow conditions. We fabricated S-TEGs with three different silicone encapsulations: hard and soft silicones, as used in previous studies, and an ultrasoft silicone sponge. We experimentally measured the elongation and cycle number to failure for stretchability evaluation as well as the open-circuit voltage and maximum power for thermoelectric performance evaluation. Thus, the S-TEG with the ultrasoft silicone sponge encapsulation showed both the highest stretchability (125% elongation to failure) and thermoelectric performance (1.80 μW cm−2 maximum power per unit area on a heater at 100 °C under natural air convection). Additionally, the S-TEG showed 153 μW cm−2 power per unit area on a heater at 100 °C under water cooling, and we confirmed its superior overall performance via comparisons with existing S-TEGs.

For the conductive patterns of electronic textiles (e-textiles), it is still challenging to maintain low electrical resistance, even under large or cyclic tensile deformation. This study investigated a double-layered pattern with different crack configurations as a possible solution. Patterns with single crack growth exhibit a low initial resistance and resistance change rate. In contrast, patterns with multiple crack growth maintain their conductivity under deformation, where electrical failure occurs in those with single crack growth. We considered that a double-layered structure could combine the electrical characteristics of patterns with single and multiple crack growths. In this study, each layer was theoretically designed to control the crack configuration. Then, meandering copper patterns, silver ink patterns, and their double layers were fabricated on textiles as patterns with single and multiple crack growths and double-layered patterns, respectively. Their resistance changes under the single (large) and cyclic tensile deformations were characterized. The results confirmed that the double-layered patterns maintained the lowest resistance at the high elongation rate and cycle. The resistance change rates of the meandering copper and silver ink patterns were constant, and changed monotonically against the elongation rate/cycle, respectively. In contrast, the change rate of the double-layered patterns varied considerably when electrical failure occurred in the copper layer. The change rate after the failure was much higher than that before the failure, and on the same order as that of the silver ink patterns.