In Case You Missed It
Electromigration
“Comparison of Electromigration in Tin-Bismuth Planar and Bottom Terminated Component Solder Joints”
Authors: Prabjit Singh, et. al.
Abstract: Electromigration monitoring of bottom terminated component (BTC) solder joints is limited to electrical resistance measurements of the solder balls. Tracking the microstructural evolution such as bismuth segregation in tin-bismuth solder balls is typically performed via metallurgical cross-sectioning, a destructive technique. Once cross-sectioned, the solder ball is not available for further electromigration current stressing. A novel planar solder geometry has been invented and developed that allows real-time, nondestructive monitoring of solder microstructure, while the progress of electromigration can be concurrently tracked via electrical resistance means. Planar solder joints are easy to fabricate in a typical metallurgical laboratory. If the electromigration behavior of the planar and the BTC solder joints happen to be similar, the planar solder joint approach could greatly aid in the quick development of solder alloys by comparing rates of electromigration and metallurgical changes in planar solders of various compositions. In this work, the electromigration rates and behavior of eutectic SnBi alloy in planar and in BTC solder joints were compared and shown to be similar. This important finding opens the use of planar solder joints for the quick and low-cost development of low-temperature solder alloys. (Journal of Surface Mount Technology, November 2024, https://doi.org/10.37665/aha4dx58)
Flex Circuits
“Pressure-Constrained Sonication Activation of Flexible Printed Metal Circuit”
Authors: Lingxiao Cao, et. al.
Abstract: Metal micro/nanoparticle ink-based printed circuits have shown promise for promoting the scalable application of flexible electronics due to enabling superhigh metallic conductivity with cost-effective mass production. It is challenging to activate printed metal-particle patterns to approach the intrinsic conductivity without damaging the flexible substrate, however, especially for high-melting-point metals. Here, the authors report on a pressure-constrained sonication activation (PCSA) method of printed flexible circuits for more than dozens of metal (covering melting points from room temperature to 3422°C) and even nonmetallic inks, which is integrated with the large-scale roll-to-roll process. The PCSA-induced synergistic heat-softening and vibration-bonding effect of particles can enable multilayer circuit interconnection and join electronic components onto printed circuits without solder within 1 sec. at room temperature. The authors demonstrate PCSA-based applications of 3-D flexible origami electronics, erasable and foldable double-sided electroluminescent displays, and custom-designed and large-area electronic textiles, thus indicating its potential for universality in flexible electronics. (Nature Communications, September 2024, https://doi.org/10.1038/s41467-024-52873-7)
Sustainability
“Leaftronics: Natural Lignocellulose Scaffolds for Sustainable Electronics”
Authors: Rakesh R. Nair, et. al.
Abstract: The global rise in electronic waste is driven by the persistent use of glass, epoxy, and plastic substrates owing to their cost, stability, flexibility and transparency. This underscores the need for biodegradable alternatives with similar properties. This work shows that leaf-derived lignocellulose scaffolds can stabilize bio-sourced, solution-processed polymers by acting as natural sequestering media. Such reinforced films, even when based on gelatin (Tg ~60°C), can endure processes over 200°C. The authors demonstrate dip-coated ethyl cellulose films for commercially viable reflow soldered circuitry. The films offer high flexibility, more than 80% transparency, and surface roughness below 5.5nm. Advanced OPDs and OECTs fabricated on these films perform comparably to those on glass and the low material cost and simple fabrication process yields a minimal carbon footprint of 1.6kgCO2/m2. This work thus opens a vista of possibilities for biodegradable polymers heretofore considered unsuitable for making temperature-stable substrates for state-of-the-art electronics applications. (Science Advances, November 2024, https://doi.org/10.1126/sciadv.adq3276)
Wearables
“Revolutionizing Wearable Technology: Advanced Fabrication Techniques for Body-Conformable Electronics”
Authors: Ruilai Wei, et. al.
Abstract: With the increasing demand for wearable electronic products, there is a pressing need to develop electronic devices that seamlessly conform to the contours of the human body while delivering excellent performance and reliability. Traditional rigid electronic fabrication technologies fall short of meeting these requirements, necessitating the exploration of advanced flexible fabrication technologies that offer new possibilities for designing and fabricating flexible and stretchable electronic products, particularly in wearable devices. Over time, the continuous development of innovative fabrication techniques has ushered in significant improvements in the design freedom, lightweight, seamless integration, and multifunctionality of wearable electronics. Here, the authors provide a comprehensive overview of the advancements facilitated by advanced fabrication technology in wearable electronics. It specifically focuses on key fabrication methods, including printed electronics fabrication, soft transfer, 3-D structure fabrication and deformation fabrication. By highlighting these advancements, it sheds light on the challenges and prospects for further development in wearable electronics fabrication technologies. The introduction of advanced fabrication technologies has revolutionized the landscape of wearable/conformable electronics, expanding their application domains, streamlining system complexity associated with customization, manufacturing and production, and opening up new avenues for innovation and development of body-conformable electronics. (NPJ Flexible Electronics, December 2024, https://doi.org/10.1038/s41528-024-00370-8)
