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# Industry and Academia Look Toward Sustainable Circuit Boards

November 22, 2022 by Chantelle Dubois

## The shift to sustainable circuit boards may begin with minute changes to solder and substrates and larger changes to manufacturing techniques.

IDTechEx recently released a report on Sustainable Electronics Manufacturing 2023–2033, detailing the technologies and trends ahead for sustainable printed circuit boards (PCBs) and integrated circuits (ICs). IDTechEx expects that within the next decade, approximately 20% of PCB manufacturers will convert to more sustainable methods, including dry etching and printing.

##### The current structure of sustainable PCB manufacturing methods. Image used courtesy of IDTechEx

Below is an overview of some of the ways we might see PCB and IC production change to meet sustainability demands.

### Purdue Researchers Seek Out Lead-free Soldering

A research team from Purdue University led by Dr. Carol Handwerker is investigating how to make non-lead solder alternatives just as effective as lead solder, especially for critical applications. The project has resulted in the "Solder User’s Handbook," a resource that guides users in their solder practices using non-lead alloys.

In 1986, the Environmental Protection Agency (EPA) banned the use of solder or flux containing more than 0.2% lead. In 2006, the sale of electronics containing lead-based solder was banned in the European Union. The exception to both these bans is in non-consumer, high-reliability use cases, such as aerospace, defense, and certain medical devices.

##### Substrate materials. Image used courtesy of IDTechEx

Tin-lead alloys were traditionally the go-to material for electronics soldering due to their high melting point, resistance to corrosion, and electrical properties. Tin-copper-silver alloys, the most used, lead-free solder, has a higher melting temperature than tin-lead, requiring approximately 245°C to achieve wicking and wetting (as opposed to 220°C in tin-lead). This increased temperature requirement not only translates to more energy required for soldering but can also impact components such as capacitors and optoelectronics that are susceptible to damage at elevated temperatures.

Backed by a $40 million contract with the U.S. Department of Defense, Purdue researchers are developing a timeline for when lead-free solders will be as reliable as (or more reliable than) tin-lead solders in defense systems. ### The Appeal of Paper-based PCB Substrates for Flexible PCBs The IDTechEx report predicted that by 2033, the flexible PCB market will be worth up to$1.2 billion, driven by applications such as wearable devices that can benefit from non-rigid PCBs.

Most rigid PCBs are made from a fiberglass-reinforced epoxy material—fiberglass that is woven into a cloth and coated by a flame-resistant epoxy resin. This material falls into a category referred to as FR-4 (or FR4). FR4 is lightweight, strong, inexpensive, and durable in various environments, making it an attractive candidate for PCBs. However, producing FR4 creates several waste byproducts and requires petroleum-based products for the epoxy resin, making it potentially hazardous to the environment. Another material rapidly gaining popularity as a PCB substrate in flexible PCBs is a plastic called polyimide. However, like FR4, polyimide is not environmentally friendly.

Researchers are investigating alternatives to these materials, specifically in the realm of bio-based materials, like transparent cellulose nanopaper. A Japanese research team from the R&D Center for Marine Biosciences and Japan Agency for Marine-Earth Science and Technology has developed a paper-based PCB substrate that tackles the scaling and manufacturing challenges of bio-based substrates.

##### Transparent nanopaper (20 μm thickness). Image used courtesy of RSC Advances

The team reported that its paper-based substrate demonstrated low thermal expansion, thermal durability, and higher dielectric constant than other plastic-based PCB materials. The team envisions this substrate for use in flexible PCB applications, including wearable devices.

### Elephantech Turns to Additive Manufacturing

Waste materials are another challenge to PCB sustainability. In traditional subtractive manufacturing, a metallic layer, such as copper foil, coats the entire substrate layer surface. Then, the unneeded parts are dissolved. This process not only wastes metal resources but also requires many chemical compounds to achieve.

A more sustainable alternative is additive manufacturing, where instead of removing material that isn’t needed, only necessary material is added layer by layer. One example of this is Elphantech’s P-Flex, a flexible PCB. Elephantech uses a silver nano-ink to inkjet the required pattern onto a flexible PCB surface. The company then uses electroless copper plating to build up the pattern layers.

##### Elephantech's manufacturing method. Image used courtesy of Elephantech [Click to enlarge]

The company claims that this process ultimately reduces CO2 emissions by 77%, water consumption by 95%, and emission of toxic substances by 85% compared to traditional processes.

### Small Movements Make Big Impacts on Sustainability

The impact of electronics manufacturing on the environment is not an entirely new topic. In 1982, organizations such as the Silicon Valley Toxics Coalition advocated for more sustainable practices in manufacturing and electronic waste disposal to prevent those materials from contaminating the environment.

Since then, several legislations have come into effect to change how PCBs and ICs are manufactured, mitigating harmful impacts on the environment and people. While sustainability continues to be a challenge on the eve of 2023, several green initiatives, government mandates, and changes in consumer attitudes are pushing electronics manufacturers to investigate and adopt safer production practices.

Research efforts to develop reliable lead-free solder, paper-based PCB substrates, and more eco-friendly additive manufacturing techniques are small steps that may eventually make a big impact on sustainable circuit boards.

Featured image used courtesy of Elephantech.