Printed Electronics to the Rescue
In the rush to find markets for functional printing, manufacturers of printed antennas, batteries, and other innovative products may be overlooking the environmental advantage of the technology.
Printed electronics has been on the verge of commercial success for nearly a decade. The technology is capable of printing small features – on the order of 10 to 100 microns (0.4 to 4 mils) – and incorporating various materials to create circuits that include both metal lines and printed elements such as resistors. Printing conductive inks onto flexible plastic or paper sounds like a wonderfully simple way to make products as varied as antennas, cables, and batteries. In practice, adapting standard techniques such as screen, flexographic, gravure, and inkjet printing to high-volume production of electronic circuits hasn’t been as easy as proponents wished.
The potential cost advantages haven’t yet convinced entire industries to embrace printed electronics. The technology faces real limitations. Widths and spacings of printed metal lines are too large for high-end circuits and may always remain so. Microprocessors will continue to be built on rigid silicon.
But printing is suitable for applications that don’t need cutting-edge processing speed. Examples include smart RFID labels on goods, flexible displays, and even memory chips. Perhaps adding the sustainability message – save energy, save resources, save money – will push manufacturers to expand their idea of what can or should be printed.
Components that incorporate printed electronics often replace conventional printed circuit boards (PCBs), which are manufactured on rigid glass-reinforced epoxy or flexible polyimide substrates. PCB manufacturing is a wasteful process. The entire board is coated with layers of photoresist, much of which is washed away to form a pattern of lines for copper plating. Copper plating is a subtractive process that requires hazardous chemicals to etch away the unwanted material.
Printing the copper wiring in a precise pattern promises a less wasteful approach. Conductive inks, also called functional fluids, are printed in the exact pattern needed, saving material consumption and the energy required to produce those materials, not to mention avoiding caustic and toxic solvents and etchants. Printed electronics also make use of thin, flexible substrates that are usually smaller and lighter than those they are replacing.
Saving Materials and Energy
Recent studies on two example products – an antenna and an electrocardiogram (EKG) cable – compared the weight of materials used in producing conventional and printed versions. It was no contest. Printed electronics allowed the researchers to use much less material to create working prototypes. Calculations showed an 80 percent reduction in the weight of materials for the antenna and an 88 percent reduction for the EKG cable by switching from conventional to printed versions.
The weight of materials used, which includes both those wasted during manufacturing and those that end up in the final product, is not the only aspect to consider when thinking about the environmental impact of switching to printed electronics.
A life cycle assessment looks at the entire lifespan of the product – from procuring materials, manufacturing, shipping, customer use, and disposal or recycling – and evaluates the energy required and emissions to air, water, and soil.
The results on emissions are striking. Emissions during manufacturing, the carbon footprint related to the heat and electricity that the manufacturing process demands, are reduced by over 98 percent in the case of the antenna printed on a plastic substrate and 99.6 percent for the EKG cable printed on photographic paper. Manufacturing emissions for producing conventional flexible EKG cables on polyimide substrates are over 250 times the emissions released when making the same number of printed cables.
One caveat: The story isn’t quite as dramatic as it appears when you factor product lifespan into the equation. Conventional EKG cables last much longer, several years compared to a few months for printed cables. But even if switching to printed cables meant that manufacturers had to produce ten times as many cables per year, the overall savings on energy consumed and carbon footprint remains substantial. A more detailed analysis on actual use patterns (for example, would technicians discard “disposable” paper cables while they still worked well, or would they continue to use them as long as possible) would provide a better estimate of the real savings.
Applications that Reduce E-waste
Replacing fossil fuels with solar power avoids the carbon footprint associated with generating electricity, but manufacturing solar cells requires a huge expenditure of energy and materials. When solar panels reach the end of their useful life, society faces the problem of how to dispose of them. Rigid solar panels built on silicon will soon become a major contributor to the growing mountain of e-waste produced around the world.
Printed electronics technology poses a solution. Printing can’t do anything about the panels already in service, but it can stem the future production of e-waste by replacing the silicon with thin, flexible substrates. Thin-film solar cells are not a new concept, but high costs and substandard performance have delayed their adoption. A unique machine at the University of Washington’s Clean Energy Testbeds in Seattle can print solar cells on flexible plastic substrates using roll-to-roll methods. A 30-foot-wide roll of plastic sheeting passes through the machine, which deposits silver-laden conductive ink to form electrodes, heats the ink to cure it, and then applies the active layer that converts energy from the sun into electricity, allowing the entire solar-cell fabrication process to be completed with a single piece of equipment. If the technique can create solar cells with sufficient performance, such cells will be both less expensive and less resource-intensive than today’s solar panels.
Printed batteries present another opportunity for printed electronics to take the environmental high road. These paper-thin electrochemical cells can replace coin batteries or add data storage capability in applications ranging from transit and identification cards to medical patches that monitor vital signs or deliver medication. Unlike conventional batteries, printed batteries don’t contain heavy metals and are not considered e-waste. They require less energy and materials to produce and can be safely discarded at the end of their useful life.
The promise of low cost hasn’t been sufficient to propel printed electronics into the mainstream. True, touting the environmental benefits won’t get around the limitations of the technology. But by positioning printing as the more environmentally friendly option, certain products can gain traction in markets where the message of saving resources and reducing carbon footprint resonates with customers.
Read more from the October/November 2018 issue.