IGF-AIF 20732 BR
Abstract
Smart clothing can do more than dress fashionably and functionally. More and more often it shines, warms and communicates with mobile devices. For this purpose textile structures contain circuit carriers based on conductive thread materials. At the crossing points of the conductive yarns, unreliable electrical contacts often occur that do not meet the technical requirements.
Attempts with cyanide-containing silver electrolytes for subsequent metal deposition at the contact points in textile structures have not been successful in the past. Among other things, the necessary intensive cleaning has so far been ruled out for economic, health and environmental reasons. With cyanide-free silver baths, the selective metallization for galvanic contacting in textile circuit carriers has now been systematically investigated.
Problem
Conductive yarns are used for textile circuit carriers in order to produce conductive structures using textile technology. The interconnection required for this is possible using weaving technology, for example, but does not provide reliable contact points at the weave bonding points of the conductive yarns, as only a force-fit surface contact (see Figure 1) is created and not a material-fit contact as is the case with soldering, for example: The contact points are susceptible to alternating bending stresses.
The aim of the project is to produce more reliable smart textiles with better contact at thread intersections. Reduced-pollutant electrolytes are to be used to subsequently metallize conductive material in textile surfaces. The aim is to achieve more reliable contact points within woven or knitted circuit carriers through galvanic contacting and an increase in the conductivity of the conductor paths.
Solution
In the project, a cyanide-free electroplating process for partially conductive textile surfaces, suitable pre- and post-treatment steps and application-related reliability tests were developed. Since novel, cyanide-free electrolytes delivered promising results in our own preliminary tests, it is possible to electroplate partially conductive textile structures with low levels of harmful substances and at the same time to contact thread-thread contact points in a material-locking manner (see Figure 2). Although the new, cyanide-free electrolytes are around 50 percent more expensive to procure than comparable cyanide electrolytes, they can be used for longer in the process due to their oxidation stability and are not subject to any loss of quality during breaks in use.
Optimal parameters must be determined for the electroplating process and then the reliability of the contacting under stresses such as kinking, bending, chafing and moisture must be investigated (see Figure 3) and compared with the textile wiring.
For this purpose, woven test structures and a pre-treatment for the electrically conductive fabrics must be developed. Following the electroplating process, the post-treatment required to remove electrolyte residues will be investigated. Finally, concepts for transferring the technology to knitted fabrics and for industrial implementation will be developed.
Fig. 1: Microscopic image of a woven circuit carrier 
Fig. 2: SEM cross-section of a woven contact point after galvanic metallization 
Fig. 3: Dynamic tensile test with resistance monitoring
Results and Applications
The project developed a production technology in which chemically pre-metallized yarns with silver layers of less than 0.5 µm are incorporated using textile technology without significant silver abrasion and in which only the finished conductive textile structure is galvanically reinforced. It provides higher quality textile electronic circuits, conductor tracks, coils, interdigital structures and bus systems than with the direct processing of highly conductive ELITEX®. In addition, thread resistances of less than 20 ohm/m can be achieved at gauges of less than 235 dtex, which are required for induction coils in the wireless charging of cell phones, smart clothing and electric vehicles.
The contamination of non-conductive areas of textiles has so far ruled out this technology. The research project paves the way for this efficient technology with the results achieved in the investigation of cyanide-free electrolytes. With thread resistances of well below 5 Ohm/m and a fineness of less than 235 dtex, not only charging coils but also power electronic components can be integrated into textiles for the first time. In addition, electrical contacts in textiles can be realized by post-galvanizing with a classic, commercially available piece goods electroplating process.
The resistances of the subsequently galvanically reinforced yarns correspond to those of wires and strands, which are difficult to process using textile technology. If the conductive textile structures produced with chemically pre-metallized precursor yarns are reinforced with even higher layers, light and stable textile-reinforced metal composites are produced. Both the post-galvanization of electronic textiles with and without attached electronic components and the production of textile-reinforced metal composites are subsequently implemented with electroplating companies, weavers and warpers for the relevant users.
The textile electroplating developed improves the quality of textile circuit boards and heaters through more reliable contacts. Potential beneficiaries are SMEs active in the smart textiles market and SMEs that are opening up new fields of application in the field of electroplating. Areas of application exist in the automotive, protective clothing, smart home and heating textiles sectors. The process can be used without hesitation on clothing and in the sports and leisure sector. Cyanide-free textile electroplating allows products to be given a highly conductive structure at any point in the value chain. It is now possible to electroplate close-to-body products only in the assembled state. The process is also suitable for repairing defective contact points: Small breaks or missing thread-thread contacts within a luminous textile with woven wiring can be subsequently electroplated. Last but not least, the use of cyanide-free electrolytes improves the environmental compatibility of the electroplating process steps.
The final report on the project will be made available by the research center on request.
Contact
Dipl.-Ing. (FH) Julia Ullrich
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