New flexible substrate material could help fight e-waste

The continuing increase in electronic waste, also known as e-waste, is becoming a pressing global issue and is expected to become even more serious with the development of new types of flexible electronics for various applications, including single-use devices.

A newly developed flexible substrate material, a 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 cycle, but also enable the scalable production of more complex, multilayer circuits than currently used substrates.

“We recognize that electronic waste is an ongoing global crisis that will only get worse as we continue to produce more devices for the Internet of Things and as the rest of the world evolves.” says Wallin, an assistant professor in the Department of Materials Science and Engineering at MIT.

The current focus of research in this area is the development of alternative substrates for flexible electronics, which traditionally rely on a polymer called Kapton. However, most studies ignore the reasons why Kapton was originally chosen. Kapton offers numerous advantages, including excellent thermal and insulation properties and easy availability of source materials.

The polyimide industry is expected to reach a global market of $4 billion by 2030. The material is ubiquitous in electronic devices, including flexible cables that connect various components in cell phones and laptops. Its high heat resistance also makes it widely used in aerospace applications. Despite its classic status, the material has not been updated for several decades.

It is very difficult to melt or dissolve Kapton, making it unsuitable for reprocessing and a challenge for manufacturing advanced circuit architectures. The traditional Kapton manufacturing process involves slow heating for many hours at temperatures between 200 and 300 degrees Celsius.

Instead, the team developed an alternative material, a form of polyimide that is designed to be compatible with existing manufacturing methods. The material is a light-cured polymer, similar to those used by dentists for fillings, and can be cured in seconds using ultraviolet light at room temperature.

The new material has the potential to be used as a substrate for multilayer 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 bonding of layers due to difficulties in melting, this new material can be processed at low temperatures and cured quickly on demand. This could lead to new possibilities for the development of multilayer devices.

In addition, the material is designed to be recyclable, with subunits built into the polymer backbone that can be quickly dissolved by an alcohol solution and a catalyst. This allows precious metals and entire microchips to be recovered and reused from the solution to produce new devices.

“We designed a polymer with ester groups in the backbone” unlike traditional Kapton, Wang explains. These ester groups can be easily broken down with a fairly mild solution that removes the substrate while leaving the rest of the device intact. Wang notes that the University of Utah team co-founded a company to commercialize the technology.

“We break the polymer back down into its original small molecules. Then we can collect the expensive electronic components and reuse them.” adds Wallin. “We all know about the shortage in the supply chain for chips and some of the materials. The rare earth minerals that are in those components are very valuable. So we think there’s a huge economic incentive now, as well as an environmental incentive, to create those processes to recover those components.”

Magazine reference:

1. Caleb Reese, Grant M Musgrave, Jitkanya Wong, Wenyang Pan, John Uehlin, Mason Zadan, Omar Awartani, Thomas J Wallin, and Chen Wang. Photopatternable, degradable, and efficient polyimide network substrates for electronic waste mitigation. RSC Applied Polymers, 2024; DOI: 10.1039/D4LP00182F