Novel vitrimer plastics promise greener PCBs

Even the least recyclable part of the process could be recovered 91 percent of the time

A recent study proposes that vitrimer could potentially be used for making printed circuit boards (PCBs) that are much more repairable and recyclable than the ones we use today.

Conducted by the University of Washington, the study was published in Nature and concludes that vitrimer could replace thermoset plastics as one of the key materials in PCBs.

Owing to their chemical composition, PCBs aren't exactly great for the environment. "Every year the world generates billions of pounds of electronic waste, and this is one of the fastest growing waste streams around the world as we integrate electronics into all kinds of smart devices," study co-author Vikram Iyer told The Register.

"In addition to needing to extract more resources to make these devices, they also produce waste that can contaminate the air, soil and water at end of life."

A University of Washington researcher laminates a vPCB

A University of Washington researcher laminates a vPCB – Click to enlarge. Source: Mark Stone/University of Washington.

The key difference between thermosets – the kind of plastic currently used for PCBs – and vitrimer is the latter's malleability. When heated, vitrimer molecules can break bonds and form new ones, which is an unusual characteristic for polymers. Vitrimer, or vitreous polymer, was first synthesized in 2011, though practical uses for the material didn't emerge until later.

"We realized the vitrimer materials they've been developing are a perfect solution for creating recyclable circuit boards, and that we had the potential to create a material with properties similar to industry standards to accelerate adoption," Iyer explained.

The process for making a vitrimer PCB (or vPCB as the researchers call it) is mostly the same as it is for a regular PCB – the only substantial difference is that vPCBs are completely cured while traditional designs are only semi-cured.

When dipped into an organic solvent, the team found the solution transformed the vitrimer in the vPCB into a "jelly-like substance," making it swell in size and separate from the glass and other components. The process doesn't even use a chemical reaction, making even the solvent recyclable.

The researchers say they could recover all of the glass for reuse, 98 percent of the vitrimer, and 91 percent of the solvent – which is a very respectable rate for recyclability.

vPCBs also showed great promise for repairability, making it possible to fix damage like cracked PCBs since the base materials can be separated. Vitrimer is fortunately resistant enough to heat for things like heat guns, which are used to melt solder on PCBs, to work properly on repairs.

"There's certainly room to make them more robust though," Iyer conceded. "We can tune the properties to make them [vitrimers] tolerate even higher temperatures. Members of the team are currently developing AI tools to predict the properties of new vitrimers with the hope of customizing them for target applications."

vPCBs might not even raise costs much, if at all

The biggest obstacle to using vitrimer right now (assuming it proves to be a worthy successor to plastic) is cost. Since the production method for vPCBs is apparently mostly the same as typical PCBs, there won't be a price difference in that aspect – but using vitrimer instead of plastic could still be a financial obstacle.

"Our vitrimer PCBs are compatible with all of the standard processing used to pattern and make circuits, so these costs should be similar," Iyer told us.

The researchers haven't yet analyzed the potential cost difference between thermosets and vitrimers, but Iyer is hopeful. "We did however use off the shelf chemicals, and the processing steps here are largely the same as industrially produced materials like epoxy (heating, stirring, etc) suggesting it has potential to be cost competitive at scale."

Of course, those chemicals (an epoxide, acid, and a catalyst) will need to be available in quantities sufficient to feed the PCB industry, which makes tens of millions of boards every year. That's where the additional cost comes in.

On the other hand, as vPCBs could be very recyclable, there could be savings on reuse of materials, offsetting the initial cost.

As with all breakthroughs in studies though, it's uncertain whether the findings will translate into real-world products. Given that Microsoft, Google, and Amazon funded the study (Microsoft even supplied a researcher), it definitely has potential to make it out of the lab and into actual electronics. ®

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