Printing microelectronics with copper at scale gets closer to reality

Copper has a long history in the electronics industry, but it could be the new standard for printing microelectronic products more sustainably.

A team of Canadian researchers from both academia and industry have been able to demonstrate that printed copper circuits have potential to reduce chemical consumption compared to current PCB technology, meet reliability standards, and reduce overall printing costs.

The research was a collaboration between C2MI, Canada's largest microelectronics R&D center, and École de technologie supérieure (ETS), a research university in Montreal, Canada. In an interview with Fierce Electronics, Christophe Sansregret, process development engineer in printed electronics and microelectronics assembly at C2MI, said the research goes back to 2019 as part of an effort to develop more sustainable printed circuit board (PCB) manufacturing technologies – today’s processes are not especially green.

“There's a big push in the semiconductor space on sustainability and greening the business overall,” Sansregret said. “The materials waste is part of it.”

Today, most of the semiconductor industry is using silver for printing, which has reliability issues. The silver reacts with the air and the humidity in the air, making small dendrites, Sansregret explained. “If you don’t have a mechanical barrier, then this will create short circuits.” This electromigration issue with silver has been known for decades, he said, and the research into copper printing was motivated by a desire to find a viable alternative.

Copper has its own drawbacks. The aim of the collaborative research was to find a solution that would offer the best of both worlds – copper printing using additive technology to prevent copper waste and need for harsh chemistry that is reliable as traditional PCB technology. Sansregret said when copper is used today in traditional PCB manufacturing it results in 80% of it being wasted.

Less waste of materials reduces the cost, as well as being environmentally friendly. The researchers were able to reduce the cost of inks using copper by more than 50% when compared to silver inks, while also reducing chemical consumption compared to current PCB technology’s subtractive processes because the C2MI/ETS solution involves direct printing of circuits.

Sustainability drives printed copper interest

Research into copper is part of a broader push to develop more sustainable methods of making electronic devices.

Ravi Prakash, associate professor in the electronics engineering department at Carleton University in Ottawa is part of a research lab focused on organic sensors and devices, which includes a focus on driving sustainability bioelectronics, next generation biosensors, and flexible electronics. “There are a few different angles that the researchers like me are looking at.”

That includes the substrates for printing electronics, he said, and copper is expected to have an expanded role. “Copper is heavily investigated as a material with a long-term future.” Prakash said the interest in copper innovation is in part being driven by the growth in electric vehicles and the proliferation of consumer electronics.

The semiconductor industry has always been bullish on copper, he said, but scalability has been a critical challenge to overcome when it comes to printing. “It's the most commonly used metal in the IT industry right now.”

Prakash said research at Carleton has been looking at copper deposition solution using new methods and new processes, but it’s experimental research that has a long way to go. “Now we can incorporate high density printed copper interconnects using more sustainable processes.”

Many companies have been trying to crack the copper code. Art Wall, director of fab operations for the NextFlex Technology Hub, said a major hurdle has been preventing the copper from getting overly oxidised as the ink cures. He said the industry is looking for a copper solution that’s close to bulk as possible – bulk semiconductor materials are those that are routinely available via simple chemical precipitation.

Wall said there are companies that have solutions that are addressing oxidation problem, but those solutions not universal – standards are critical in the semiconductor industry. “You need to have something that's very reliable, very repeatable, and very standardized,” he said.

Copper promises lower weight, cost

The payoff of copper printing comes in multiple ways, Wall said, not the least of which is the reduction of waste that comes with the elimination of etching and patterning. Aside from the environmental benefits, he said, the economic benefits are significant in terms of the reducing the CAPEX that comes with traditional lithography and etching. “CAPEX is a very important piece of the puzzle.”

NextFlex is a flexible hybrid electronics manufacturing institute focused on additive manufacturing, where the need for capital equipment is relatively modest, Wall said, and the printers available are now “ridiculously cheap.”

Printed copper is of interest to industries where the weight of a device is an important consideration, such as aerospace and automotive, Wall said, because reducing weight can lower costs. Other areas of interest are medical devices, including wearables. “The vast majority of the commercial interest that you have is coming from medical companies that are really trying to figure out how to make their devices lighter,” he said.

Being able to make lighter electronics is great incentive for cracking the copper code, Wall said, with size, weight, performance and cost all standing to benefit from scalable printed copper. Its development is following the evolution of inkjet printing, which became affordable and ubiquitous due to materials innovation. “We're very close to something similar in the world of copper,” he said. “The problem is we're trying to print things that are conductive.”

Wall said it boils down to the curing process and getting copper closest to bulk properties as possible. “These are not insurmountable ‘moon shot’ kinds of problems.”