Electronic waste, or e-waste, presents a growing global challenge, exacerbated by the increasing production of flexible electronics for applications ranging from robotics and wearables to health monitors and single-use devices. A collaborative effort between researchers at MIT, the University of Utah, and Meta has yielded a groundbreaking solution: a new type of flexible substrate material. This innovation holds the potential to not only facilitate the recycling of materials and components at the end of a device’s life but also enable the manufacturing of more intricate multilayered circuits than currently possible.
The details of this development are outlined in a paper published this week in the journal RSC: Applied Polymers. The research team, led by MIT Professor Thomas J. Wallin and University of Utah Professor Chen Wang, recognized the urgency of the e-waste crisis. “We recognize that electronic waste is an ongoing global crisis that’s only going to get worse as we continue to build more devices for the Internet of things, and as the rest of the world develops,” says Wallin.
Much of the existing research has focused on replacing conventional substrates like Kapton, a polyimide widely used in flexible electronics. However, this approach overlooks the practical reasons behind Kapton’s popularity. “That really ignores the commercial side of it, as to why people chose the materials they did to begin with,” Wallin points out. Kapton boasts excellent thermal and insulating properties, readily available source materials, and a projected $4 billion global market by 2030. Wang adds, “It’s everywhere, in every electronic device basically,” highlighting its use in flexible cables within cellphones and laptops, as well as its prevalence in aerospace applications due to its high heat resistance. Despite its ubiquity, Kapton presents a significant recycling challenge. Its resistance to melting or dissolving makes it nearly impossible to reprocess.
The team’s innovative material, also a form of polyimide, offers a solution. This light-cured polymer, similar to those used in dental fillings, hardens rapidly under ultraviolet light at room temperature. This method not only accelerates the hardening process but also allows for low-temperature operation, unlike the energy-intensive and time-consuming heating process required for traditional Kapton.
This new material’s unique properties pave the way for multilayered circuits, significantly increasing the component density within a small form factor. Traditional Kapton substrates necessitate gluing layers together, adding complexity and cost. The new material’s ability to be processed at low temperatures and harden quickly opens up new possibilities for multilayer device architectures.
The team addressed recyclability by incorporating subunits into the polymer backbone that dissolve rapidly in an alcohol and catalyst solution. This process allows for the recovery and reuse of precious metals and microchips from discarded devices. Wang explains, “We designed the polymer with ester groups in the backbone,” a departure from traditional Kapton. These ester groups break down easily in a mild solution, leaving the remaining device components unharmed. The University of Utah team has already co-founded a company to commercialize this promising technology.
Wallin emphasizes the economic and environmental benefits of this breakthrough: “We break the polymer back into its original small molecules. Then we can collect the expensive electronic components and reuse them. We all know about the supply chain shortage with chips and some materials. The rare earth minerals that are in those components are highly valuable. And so we think that there’s a huge economic incentive now, as well as an environmental one, to make these processes for the recapture of these components.”
The research team included Caleb Reese and Grant Musgrave at the University of Utah, and Jenn Wong, Wenyang Pan, John Uehlin, Mason Zadan, and Omar Awartani at Meta’s Reality Labs in Redmond, Washington. Funding for this impactful work was provided by a startup fund at the Price College of Engineering at the University of Utah.
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