E-CASE liquid metal adhesive can securely attach flexible electronics

A composite material has been created by scientists that possesses properties which make it an excellent option for flexible electronics, an emerging field.

“We discovered a liquid metal-based composite that is highly electrically conductive and strongly adhesive,” said Michael Bartlett, associate professor of mechanical engineering at Virginia Tech, in an email. “This enables robust mechanical and electrical connections between soft circuitry and rigid electrical components.”

This includes displays on computers and mobile phones, as well as wearable health-monitoring devices, various sensors on cars and airplanes, and strain gauges on roads and bridges.

“[Our liquid metal composite] overcomes several challenges in next generation flexible and soft electronics and allows us to create flexible hybrid electronics, which combine the desirable properties of soft electronics and state-of-the-art rigid electronics into a single system,” added Bartlett.

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To connect electronic components, hot solders made of metals like tin, lead, bismuth, and indium have traditionally been used. However, these solders pose challenges in flexible electronics.

“Traditional solders are rigid and brittle,” explained Wuzhou Zu, a Ph.D. student at Virginia Tech, who worked on the study. “This causes the solder to crack and delaminate when used with flexible and soft substrates as they are bent or stretched, which results in failure. Solder also requires high processing temperatures.”

Polymer-based electrically conductive adhesives can serve as interconnects in flexible devices, but they have certain drawbacks. Their conductivity is relatively low, and the adhesive strength is generally poor.

To address these issues, the team behind a recent study published in the journal Advanced Functional Materials developed a composite material consisting of liquid metal microdroplets of eutectic gallium-indium (EGaIn), silver microflakes, and a flexible epoxy matrix. This material, which the researchers named E-CASE (electrically conductive adhesive with silver and EGaIn), can be processed at low temperatures through methods such as stencil printing and 3D printing. It can be used with flexible circuit materials that traditional high-temperature solder cannot.

The experimental study demonstrated E-CASE’s impressive adhesive strength, conductivity, and remarkable mechanical properties. A strip of this material adorned with multiple LEDs could withstand a tight bending radius of about 1 mm without LED failure and even supported the weight of a car driving over it.

“We hope that this material can play a role in several areas in electronics, robotics, and sensors,” stated Barlett. “As the use of flexible and hybrid circuits grows in fields such as wearable electronics, biomonitoring, soft robots and more, creating robust electrical and adhesive connections at soft-rigid interfaces will be key.”

The material tested in laboratory experiments has been successful in hybrid electronic systems. However, there may still be challenges in scaling it up for widespread industrial use. Tyler Pozarycki, a Master’s student who worked on the project, explains that optimizing processing parameters and developing a better understanding of the material’s long-term performance will be necessary for scalability in manufacturing. Despite these hurdles, the team hopes that their study will lead to a technological breakthrough in many vital industries, rather than just remaining a scientific experiment.

“It would be important to refine the manufacturing process to achieve consistency in microfabrication,” concluded Zu. “This can be particularly challenging at large scales, and a deeper understanding of the process parameters, integration techniques, and characterization approaches will be important.”

This news is a creative derivative product from articles published in famous peer-reviewed journals and Govt reports:

1. Pozarycki, Tyler A., et al. “A Flexible and Electrically Conductive Liquid Metal Adhesive for Hybrid Electronic Integration.” Advanced Functional Materials (2024): 2313567.
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3. N. Ilyas, A. Cook, C. E. Tabor, Adv. Mater. Interfaces 2017, 4, 1700141.
4. B. H. Kim, F. Liu, Y. Yu, H. Jang, Z. Xie, K. Li, J. Lee, J. Y. Jeong, A. Ryu, Y. Lee, D. H. Kim, X. Wang, K. Lee, J. Y. Lee, S. M. Won, N. Oh, J. Kim, J. Y. Kim, S.-J. Jeong, K.-I. Jang, S. Lee, Y. Huang, Y. Zhang, J. A. Rogers, Adv. Funct. Mater. 2018, 28, 1803149.

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