Printed Electronics Test Center Network
Printed Electronics is a multi-billion dollar industry waiting to happen. Although the key technologies are now in place and fairly well understood, the industry is still working to develop methods for mass-producing profitable, commercial products.
One of the challenges facing product developers is the sheer complexity of the science and technology involved. PE requires a mastery of several technologies and processes in complex combination. The developer has to find the right ink, applied in the right way, on the right substrate, using the right sintering energy levels. To move from an idea to a marketable product, a developer not only has to assemble the necessary technologies and the expertise to use them, but must also conduct numerous tests in an effort to understand the specific properties and processes that will produce the desired electronic performance. Thus, lack of access to technology, expertise and past experience are creating a hurdle that is slowing down research and product development in this important field.
To address this problem, a consortium of manufacturers, integrators, and universities, led by Xenon Corporation, has formed the Printed Electronics Test Center Network. The members of the Network are making their laboratories, equipment, and expertise available to product developers and researchers, in some cases for a fee to cover lab time and costs. In addition, all labs have agreed to share research and test results among participants to accelerate commercial product development.
This article explains how the program works, the labs and expertise available, and gives examples of how access to the technology and data accumulated by the Test Center Network can be used to address specific challenges in Printed Electronics product development.
Global Test Center Network
Since May 2012, the PE Test Center Network includes 18 world-class laboratories at strategic locations in the U.S. and internationally (Figure 1). More laboratories will be added to the network over time, so interested parties should contact Xenon (for an updated list of locations.
To join the network, a lab must offer one or more relevant PE technologies and agree to make their expertise available to product developers, along with equipment and lab time. Sintering equipment from Xenon is available at all participating labs, along with technical support from the company's pulsed light engineers. Labs may also offer thermal drying and other sintering systems. Lab time will be available at most labs either free, for the simplest tests, or for a nominal fee to cover lab time and costs.
Participating laboratories offer various capabilities, depending on their expertise, to assist product developers in their practical research in such areas as:
- Behavior of conductive inks through various dispensing systems
- Performance of inks on various substrates
- Energy requirements for sintering in various processes
- Electrical performance resulting from various materials and processes
Developers who wish to access one of the laboratories may visit the location in person, or work remotely by sending materials to the lab where the requested tests can be conducted and the results sent back to the developer.
A critical aspect of the Test Center Network is the sharing of information among participants. Our vision is that by having strategic collaborations from companies with disciplines in dispensing, formulations and substrates, end users will have a network for expediting the testing of their PE ideas in a controlled, supportive environment.
The ultimate goal is to build a database of basic but essential information about the material behavior and electrical properties that result from different materials, processes, sintering techniques and other variables related to printed electronics.
Each lab agrees to make their research results transparent and available to all the participants, both the labs and the other researchers. The Test Center Network will of course respect all NDA agreements, but we and our partners believe it is important for this industry to build a shared knowledge base of processes and applications, so that each developer does not have to reinvent the wheel. The details of how the research information will be shared are still being worked out, but possibilities include teleconferences, newsletters, online forums or a dedicated web site.
The rest of this paper will discuss how some of the labs in the Network are working with developers to overcome the challenges of PE commercialization.
Properties of metal inks—how they are applied to substrates and their electronic performance once cured—are the focus of intense investigation by many researchers. Several members of the Test Center Network specialize in inks, including Intrinsiq Materials, located in Rochester, New York.
Intrinsiq develops nano-based metallic inks primarily for Printed Electronics (Figure 2). The company offers copper inks, and nickel and silicon inks are in development. Intrinsiq specializes in copper inks with low temperature sintering requirements, with no removal process afterwards, which results in a simple and clean process. They are currently working with product developers to validate processes for applications such as displays and medical instruments.
In addition to inks and photonic sintering, Intrinsiq's laboratory provides several dispensing systems, including inkjet and screen printers, and has expertise with a variety of substrates including paper, PET, and silicon glass.
Sujatha Ramanujan, Ph.D., VP at Intrinsiq, said that the challenge with inks is not only the ink itself, but how it performs within a process for a specific application."Often the technical challenge is not as great as the practical challenge, finding the right combination of materials and sintering energy that will result in the desired performance, at a manufacturing speed that can be commercialized."
Intrinsiq's work in thin film systems is an example of this. Janet Heyen, engineering director, said, "For thin-film systems, we have demonstrated the impact of the thermal characteristics of the curing environment on sintering performance. We have been able to achieve more effective sintering, and as a result, improved product performance, by tuning the properties of the material to the system being cured. This type of system optimization allows developers to achieve functionality at reduced laydowns and lower cost."
The dispensing of inks onto substrates through various printing technologies is being explored by several partners in the Network. The method, timing and quantity of ink that is applied to a substrate are all factors in ultimate electrical performance.
SonoPlot, in Middleton, WI, is addressing the challenge through material deposition technology originally developed for biological micro arrays. These printers use controlled ultrasonics to plot small volumes of material for research and development purposes. The company is working with research-based universities, Department of Defense, science and technology institutes, large R&D organizations, and early-stage technology companies.
SonoPlot's Test Center lab provides their own printing systems, a Xenon sintering system, and a thermal curing system.
SonoPlot is particularly focused on helping developers work with higher viscosity, higher solids content inks than is typically possible with many printing systems (Figure 3). This produces thicker printed features, which if sintered properly can result in greater electrical conductivity. This has opened up new applications for researchers that who require small features with improved conductivity.
Glen Donald, CEO of SonoPlot, said that he sees new interest and researchers coming into the field of PE every year. "As research expands, people are looking into different materials, particles, viscosities, surface tension, and the many other factors involved in putting ink on substrates. Ink materials have been limited by available dispensing systems to relatively narrow metrics for some key characteristics. Our focus is to help develop alternative printing technologies to address challenges that may be beyond the capabilities of other dispensing technologies."
Dispensing systems for Printed Electronics are also the focus for Integrity Industrial Ink Jet Integration, in Lebanon, NH. Integrity has deployed inkjet printing technology in manufacturing production lines for applications outside of printed electronics, and is now focused on working with end-users and developers to create single-pass manufacturing processes for PE.
The company's lab (Figure 4) includes various industrial inkjet print platforms that can drive a variety of industrial print heads. The lab has expertise in most inks and substrates, and includes a Xenon sintering system.
The company is doing advanced research in fluid and drop control on substrates. Using instruments at Integrity's lab, researchers can also study drops in flight—how ink is ejected from print heads—in microscopic detail, to learn how different trajectory and size of drops relate to performance of the sintered conductive ink. This information can be shared across the Test Center Network to build a knowledge base of ink performance.
Integrity offers lab services and tools to help clients get through the various stages of the development process—from process feasibility to commercial implementation—by providing engineering services and leveraging their experience in manufacturing industrial printing systems. Rich Baker, president of Integrity, said, "The industry is still at the early stages of commercial processes. A key step will be the ability to print metal inks (as well as all other fluids) in a single pass, at 100+ feet per minute. Most volume production requires high-speed single-pass processing where the deposition drying and sintering needs to occur within a fraction of a second. It is in this process development where we come to bear. There is typically an innovation required to make the printing work at production speeds."
Once ink has been deposited on the substrate by a printing process, it must then be converted into a solid uniform layer of conductive material through sintering. There are several possible sintering techniques, including thermal ovens, arc discharge lamps, laser and pulsed light.
Xenon's sintering technology (Figure 5) is based on pulsed light, sometimes called photonic sintering, which provides the energy needed to treat inks without harming substrates, and at speeds compatible with printing processes such as gravure and flexography, an important requirement for many commercial applications. Sintering is also effective when multilayer circuitry is needed.
Xenon's sintering systems are available at all Test Center locations, which includes Xenon's own headquarters laboratory in Wilmington, MA, where there is also expertise in a wide range of inks, printers and substrates, with experience in diverse applications.
Much of the work at Xenon labs and with product developers is in the area of copper inks, which pose special challenges in Printed Electronics. Copper oxide is non-conductive and copper oxidizes more readily. For this reason copper nanoparticles require some form of coating to prevent them from oxidizing. These coatings can be a protective polymeric or metallic shell which must be removed during the sintering process. Also, the energy required for sintering copper is significantly higher than for silver.
Saad Ahmed, Ph.D., manager of engineering at Xenon, said, "With copper, there can sometimes be a small margin between the energy required to sinter, and the point at which material is destroyed. Our sintering systems provide extremely accurate control, so that we can meet the narrow requirements of these applications."
The challenge for any application is to match the energy and timing of the pulsed light to achieve the proper electrical performance. This is dependent upon the specific materials and application, and always requires experimentation.
The overarching challenge for virtually all applications in Printed Electronics is understanding the relationship between ink, film thickness and energy requirements for drying, and how all of those factors affect electronic performance.
This overall challenge is being explored by Western Michigan University's Center for the Advancement of Printed Electronics (Figure 6). The goal of the Center is to provide a facility for research, development and application of materials for the fabrication of flexible electronic devices on printing presses. The center contributes to the advancement of the printing, paper, and electronics industries, and their suppliers through material design and analysis, device prototyping, device testing, press engineering, press-setup, education and training.
The Center utilizes a multidisciplinary approach to research, combining faculty across multiple departments and multiple colleges. The WMU laboratory has technology and expertise in all areas of printed electronics, including major printing processes (inkjet, roto gravura, flexo graphic, screen printing, and offset printing), sintering (Xenon sintering and thermal ovens), and a wide range of inks and substrates, as well as advanced instrumentation for the study of all materials and electrical performance.
Margaret Joyce, Ph.D., director of the Center, said, "It's important to gain an understanding of how the energy requirements of sintering relate to electronic performance for a given material on a given substrate. We help researchers understand the behaviors of a broad range of materials and processes, the resulting electrical performance, and cost analyses to determine if an approach is practical."
The WMU Center is also addressing other challenges in PE, such as online registration on smaller print areas. Registering on high-speed presses is challenging because printed layers are optically transparent. Precision PE manufacturing is vital for defining the feature size (the minimum width of the traces and gaps between adjacent traces), and this is often far more difficult on flexible substrates than on rigid ones.
This article has presented some of the laboratories and technologies available in the PE Test Center Network. We should stress that there are many other partners in the Network who are also advancing the commercialization of printed electronics through technology, products and research, and only space limitations prevent their inclusion here.
Many challenges still exist before printed electronics becomes a viable commercial technology, but most researchers believe this achievement is only a year or two away. The shared vision of all members of the PE Test Center Network is to support research and development, share knowledge across the Network, and through these efforts, to advance the practical use of Printed Electronics in commercial applications.
Lou Panico is president and CEO of Xenon Corporation. One of the founding principals of the company, he has authored numerous technical papers on Pulsed Light Technology and its application in various industries. He holds a degree in Electronic Engineering from Northeastern University and is a veteran of the U.S. Marine Corps. He can be reached at firstname.lastname@example.org.