The continuous growth of electronic waste, also known as e-waste, is becoming a pressing global issue, and it is projected to exacerbate with the development of new types of flexible electronics for various applications, including single-use devices.
A newly developed flexible substrate material, a result of collaboration between MIT, the University of Utah, and Meta, has the potential to not only facilitate the recycling of materials and components at the end of a device’s life but also enable the scalable manufacture of more complex multilayered circuits compared to existing substrates.
“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, an assistant professor at MIT’s Department of Materials Science and Engineering.
The current focus of academic research in this area is the development of alternative substrates for flexible electronics, which traditionally rely on a polymer called Kapton. However, much of the research has overlooked the reasons why Kapton was initially chosen. Kapton offers numerous advantages, including excellent thermal and insulating properties and easy availability of source materials.
The polyimide industry is expected to reach a $4 billion global market by 2030. This material is ubiquitous in electronic devices, including the flexible cables that connect various components in cell phones and laptops. Its high heat tolerance also makes it widely used in aerospace applications. Despite its classic status, the material has not been updated for several decades.
It is extremely difficult to melt or dissolve Kapton, making it unsuitable for reprocessing and challenging the manufacturing of advanced circuit architectures. The traditional manufacturing process for Kapton involves slow heating for hours at temperatures ranging from 200 to 300 degrees Celsius.
In contrast, the team has developed an alternative material, a form of polyimide, that is designed to be compatible with existing manufacturing methods. This material is a light-cured polymer, similar to those used by dentists for fillings, and can be hardened within seconds using ultraviolet light at room temperature.
The new material has the potential to be used as a substrate for multilayered circuits, offering a way to significantly increase the number of components that can be accommodated in a small form factor. Unlike the previously used Kapton substrate, which required gluing the layers together due to its difficulty in melting, this new material can be processed at low temperatures and quickly hardened on demand. This could lead to new possibilities for the development of multilayer devices.
Additionally, the material is designed for recyclability, with subunits incorporated into the polymer backbone that can be rapidly dissolved using an alcohol and catalyst solution. This enables the recovery and reuse of precious metals and entire microchips from the solution for the production of new devices.
“We designed the polymer with ester groups in the backbone,” unlike traditional Kapton, Wang explains. These ester groups can be easily broken apart by a fairly mild solution that removes the substrate while leaving the rest of the device unharmed. Wang notes that the University of Utah team has co-founded a company to commercialize the technology.
“We break the polymer back into its original small molecules. Then we can collect the expensive electronic components and reuse them,” Wallin adds. “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.”
Journal reference:
- Caleb Reese, Grant M Musgrave, Jitkanya Wong, Wenyang Pan, John Uehlin, Mason Zadan, Omar Awartani, Thomas J Wallin and Chen Wang. Photopatternable, Degradable, and Performant Polyimide Network Substrates for E-Waste Mitigation. RSC Applied Polymers, 2024; DOI: 10.1039/D4LP00182F