Sandia researchers have been working on an innovative way to build multilayer electronic components that are smaller, more flexible, and complex than those produced for standard electronic packaging.
Called "direct-write," it uses a computer-automated device for precision printing of ceramic and metallic slurries on a substrate. The electronics are "drawn" on the base with an ink-filled nozzle, rather than being screen-printed or etched. This allows them to be built using a variety of materials and printed in complicated shapes.
The printing is done using a commercial system, called a Micropen, which is manufactured by OhmCraft, Inc. of Rochester, N.Y. The Sandia group has worked with OhmCraft and several other companies through a program sponsored by the Defense Advanced Research Projects Agency (DARPA) to explore the potential of this approach for depositing a breadth of materials — including conductors, high-value resistors, magnetic materials, and chemically sensitive elements — in precise patterns.
"This new system is extremely valuable for rapid prototyping of electronics and is ideally suited for fabricating highly customized circuits, which are especially appropriate for Sandia technologies," says Duane Dimos, Manager of Ceramic Materials Dept. 1843. Duane has been involved with the project since its inception four years ago. "Without having to make tooling, such as screens or masks, we can build high-precision electronic parts in a short period of time to let engineers know quickly if their design works."
The system also allows electronics to be constructed in unusual and complex patterns. For example, a communications chip manufactured in this manner could potentially be small and flexible enough to be fabricated on a soldier’s helmet or as an integral part of any odd-shaped object.
Sandia and its DARPA partners have already used the technique to build a number of prototype antennas in unusual shapes for Navy applications, which are currently being tested.
Duane says the technique is similar to one developed by Joe Cesarano (1843) to fabricate free-form ceramics, called robocasting, which relies on robotics for computer-controlled deposition of ceramic slurries — mixtures of ceramic powder, water, and trace amounts of chemical modifers — through a syringe.
In contrast, this work uses a variety of metallic and ceramic slurries or "inks," to write intricate patterns for precision circuitry. The electronic inks are heated at low temperatures to evaporate any fluids, leaving behind the dried metal or ceramic, and then fired to sinter the powders together.
To date, the most complex direct-write components consist of 13 printed layers. Pin Yang (14192) has led the effort to fabricate devices such as integrated RC filters, multilayer voltage transformers, resistor networks, and other components.
Paul Clem (1846), one of the project’s leaders, says that two aspects of the direct-write system make it useful. First, the Micropen can deposit fine line traces or areas on nonplanar substrates, and, second, slurries (inks) can be custom-designed for specific needs and specific functional components.
"The Micropen can use nozzle sizes from 2 mils (50 microns) to 100 mils to obtain different print geometries, such as fine line traces or filled dielectric regions," Paul says.
Other inks that have been developed by Sandians include resistors, magnetic materials, and porous chemical sensors.
Chemist Nelson Bell (1843) is studying the area of slurry modification for the project. He says that although a number of commercially available slurries/inks are available and suitable, he is looking at changes in powder materials, solvents, binders, wetting agents, and drying control agents that can improve the printing and performance of the inks.
"We want to come up with the best possible slurries to avoid clogging the printing tip to control flow and line shape during printing, and shrinking after firing," Nelson says. "All these aspects have to be taken into consideration."
Paul says the current challenge for the research team is working with lower temperatures in the final firing stage. The goal is to put these multilayered electronic components on substrate materials such as plastic that can’t withstand high temperatures.
"We have redesigned many of these materials so that we can achieve the same performance by heating the parts up to only 300-400 degrees C instead of 850 degrees C," Paul says. "We should be there soon."
Philip Gallegos, Manager of Electronic Fabrication Dept. 14112, who has several customers interested in exploring this technology, calls this a "very interesting technology."
"We are looking for new ways to apply this technology to fabricate electrical/mechanical prototypes from 3-D model-based design," Phillip says.