Aerosol Jet: Better Electronics Through Spraying

Chances are, when you think “aerosol,” cans of paint or hair spray or the like come to mind. Solar cells, sensors, resistors, flat-screen panels, circuits, antennas, and touch screen displays don’t. Yet an innovative technology developed by Optomec (optomec.com) under a contract for the DARPA Mesoscopic Integrated Conformal Electronics (MICE) program uses aerosol jet printing technology for the additive creation of products like these. While the process is still in the developmental stage in regards to printing electronic components, it holds great potential. Reasons for this include:

•    Precision: It’s able to create parts as small as 10 microns with layer thicknesses in the nanometers.
•    It’s able to work with a variety of high-viscosity materials, from polyesters and polyimides to metals, pastes and nanoparticle inks.
•    It can print onto substrates of virtually any shape and size.
•    It can remanufacture damaged or worn electronic components.

Aerosol jet works similarly to conventional 3D printing processes: A CAD file is converted into stereolithography (STL) format and uploaded into an aerosol jet system. The system focuses a high-definition beam of liquidized material toward a substrate, additively building on it. The beam exits the nozzle at 50 m/second. This high exiting speed keeps the beam collimated for high resolution to be maintained during its deposition.

Optomec has developed two families of aerosol jet machines: OEM systems, for integration into automation platforms, and laboratory systems, so researchers can continue to develop next-generation electronic components and new processing materials. They’ve been sold to companies ranging from Boeing to BP Solar. And while this equipment has been sold, Ken Vartanian, Optomec marketing director admits, “The majority of systems we have sold are still in the lab, but we’re seeing development work starting to come to fruition.” He says actual aerosol jet-printed electronics could enter the market this year.

Not Ink Jet
“One of the first things people immediately think of when they hear ‘aerosol jet’ is ‘oh, this is an ink jet printer,’” says Vartanian. “It’s not—it’s nothing like that.” Industrial ink jet printers are what Vartanian calls “incumbent technology” for printed electronics. They use the same basic technology as today’s home and office desktop printers. However, they work primarily with metal loaded inks with viscosity ranging from 8 to 12 centipoise (cP)*. Conversely, aerosol units print with a wider range of materials and at much greater viscosities, from 20 to 1,000 cP.

“The droplet sizes that are used in ink jet are much larger than aerosol jet,” says Vartanian. “So consequently, the features that they can print are not as fine, not as high resolution. We’re dealing with very, very fine feature sizes. Because of our droplet size, we can put down very, very thin coatings of the nanometer.”

Furthermore, ink jet systems can only build on flat substrates, whereas the aerosol process is able to work on substrates of various non-planar surfaces. “The application opportunities and the opportunities for deposition of various materials on various substrates are much higher with aerosol jet,” Vartanian says.

Applications
Alternative energy is a particular market of focus for the technology, specifically in solar cell fabrication. Researchers at the National Renewable Energy Lab (NREL), University of New South Wales (UNSW) and Fraunhofer Institute for Solar Energy Systems have created solar cells yielding 20% efficiency with the aerosol jet process. Solar cell efficiencies created through conventional processes typically only offer 16 to 18% efficiency.

“One of the key features of solar cells that determine how well they convert sunlight into energy are collector lines,” Vartanian says. These are grids of lines located on top of the solar panel, facing the sun. “The collector lines not only collect sunlight, but they also block some of the sunlight from reaching the wafer,” he says. “This is called the shadowing effect.” The narrower the collector line, the more sunlight that reaches the wafer. Today’s processes create collector lines 80 to 100 microns wide. Aerosol jet can print the lines half that width.
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*Centipoise is a measure of dynamic viscosity, or the ability of liquids to flow. For example, water is measured at 1 cP, while honey is measured at 1,000 cP.