Flexible Hybrid Electronics (FHE) have been used to fabricate multi-layer circuits that are conformable, low-cost and suitable for a wide variety of applications, from smart packaging, connected healthcare, intelligent industrials to efficient infrastructure. This technology can attach traditional SMT devices to printed traces on flexible, stretchable substrates such as plastic and textile. For further information see the IDTechEx report on Printed, Organic and Flexible Electronics 2020-2030: Forecasts, Technologies, Markets.
One industry forecast predicts that the market for printed and flexible electronics will more than double from 2018 to 2029. According to web of science, there has been a significant increase in publications on FHE in the past five years. To bridge the gap between conventional PCBs and Flexible Hybrid Electronics, researchers at the University of Florida (UF) in collaboration with Jabil, have been leading an effort through the NSF-funded Industry/University Cooperative Research Center on Multi-functional Integrated System Technology (MIST) for FHE devices and systems.
The research team, led by Dr. T. Nishida and Dr. Z. H. Fan in collaboration with Jabil, has developed enabling methodologies and technologies in the areas of component attachment, via filling, surface modification2, and novel flexible devices. One recently developed example was a flexible wireless power transfer coil which can be used for charging implants and low power IoT devices (Fig. 1 (a)). Adding SMT components on the same substrate as the coil can make IoT devices thinner, lighter and conformal in practical use. UF doctoral candidate K. Sondhi completed a portion of the work at Jabil's FHE process development labs in St. Petersburg, Florida, led by Dr. J. Richstein using traditional PCBA manufacturing equipment and processes. Such hands-on collaboration provides students opportunities beyond the classroom and laboratory environment with experiential industrial learning and a pathway to innovation.
In a study that was recently accepted for presentation during ECTC 2020, the team developed a new method to improve the endurance to bending by reducing the Young's moduli mismatch between SMD solder joint and substrate. The latest results on component adhesion will be presented during ECTC 2020, May 26-29 in Orlando. Since this method can be used to increase the adhesion of components on flexible substrates without changing the solder joint moduli (Fig. 1 (b)), a similar approach can be employed for multiple low-temperature solder pastes on flexible circuits. Results from the same study demonstrated a 3-fold increase in the shear strength of the component attachment to the plastic substrate with printed traces.
Successful demonstrations of SMD attachment on flexible circuits and reliable via filling advances a technology roadmap for mechanically pliable multi-layer devices on plastic substrates such as polyethylene terephthalate (PET) and thermoplastic polyurethane (TPU). These materials are used in the manufacturing of everyday products, and the ability to create such hybrid circuitry can make devices smart and attractive without adding bulky traditional electronics. Such devices have many applications in our day-to-day life such as smart packaging, healthcare, transportation, industrial IoT, and defense sectors.
(a) Effect of bending radii on the B-field of the EWPT coil, and (b) demonstration of the solder joint characteristics before and after the protocol.
2.Web of Science: https://wcs.webofknowledge.com/RA/analyze.do?product=WOS&SID=7AninApO9lvYxWn3MoP&field=PY_PublicationYear_PublicationYear_en&yearSort=true
3. Sondhi, Kartik, et al. "Airbrushing and surface modification for fabricating flexible electronics on polydimethylsiloxane." Journal of Micromechanics and Microengineering 28.12 (2018): 125014.
4. Sondhi, K., et al. "Flexible screen-printed coils for wireless power transfer using low-frequency magnetic fields." Journal of Micromechanics and Microengineering 29.8 (2019): 084006.