Engineering know-how for printed electronics



The ongoing development of printed electronics continues unabated. This particularly attractive technology is complementing classic silicon microelectronics with thin, lightweight and flexible technologies such as affordable data memory, flexible displays and printed batteries. However, there are still a few hurdles to overcome in the development of established processes.

Organic and printed electronics make several new applications possible and have already successfully established themselves on the market with various products. Many other applications are on the threshold of laboratory activities and production prototypes. "Flexible electronics are making their way into a number of products that we use on a daily basis - in many cases without users even noticing," says Wolfgang Mildner, Managing Director of PolyIC, explaining the state of the art. They are on their way to establishing new applications in microelectronics," explains Mildner: "Organic photovoltaics, touch sensors, flexible displays, OLEDs as lighting or TV and tablet displays, data memories and circuits are still considered the largest growth sector in the medium term.

Acceptance of organic electronics is also growing in the automotive industry. Stephan Berlitz, Head of Development for Lighting Functions and Innovations Director of Light Functions/ Innovations at Audi, describes the vision being realized by the OLED 3D research project: "We are always looking for new solutions. Rear lights could be the first OLED components to establish themselves."

The 3D OLED rear light introduced at LOPEC 2013 proved that this technology is opening up new possibilities for car designers. Large free-form headlights with conventional LEDs whose surfaces fit the shape of the car's body three dimensionally already have an enthusiastic following. Berlitz is certain about one thing: "In the future, headlights and fenders will merge to form a single component and no longer be defined as separate parts."

Overcoming "Red Brick Walls"
A great deal of progress has been made during the past few years, a fact that will be reflected at LOPEC, the leading international event for printed electronics. The exhibition will demonstrate the growing appeal of organic electronics. It concentrates on functional integrated system solutions and addresses industrial end users. At the same time, it presents the entire value chain and gives system manufacturers a large platform. Take the LOPEC Demo Line, for example: This live production line gives visitors an overview of the entire production process for printed electronics. The live production line is a collaborative effort being coordinated by Fraunhofer ENAS. It also shows that the production of organic electronics still has a great deal of potential.

The combination of printing techniques and new functional materials makes it possible to manufacture very cost-effective electronic products. Higher-performance materials and more precise manufacturing processes are needed for more complex applications. "It is a complicated combination of material, device architecture and processes," explains Wolfgang Mildner from PolyIC. To be used as printed electronics, polymers must be very homogenous and printed together on flexible substrates. These requirements far exceed those of graphic printing. "Special requirements call for intense cooperation between competent material manufacturers and subsequent producers," explains the expert.

Due to these complex relationships, the challenges are still considerable, which is why the current issue of the OE-A roadmap refers "Red Brick Walls", i.e. a fairly high hurdles that must be overcome. Generally critical aspects include mass-production techniques, small structures with resolutions less than 10 μm, and reliable verification of the layer thickness and the drying properties. The ambient conditions in which organic electronics are manufactured are another aspect: They are usually produced under cleanroom conditions or in an inert gas environment. Above all, however, registration is still the real challenge: Various layers of structured functional materials are placed on top of one another with extreme precision. An exact inspection is required to ensure that the structures are aligned with one another.

There are also some unanswered questions regarding the materials being used. Organic electronics are not only based on conductive polymers, but also on polymers with semiconductor properties or smaller molecules from organic chemistry. Manufacturers such as Heraeus Precious Metals, Electronic Materials Division, are developing and producing conductive polymers that are increasingly being used as electrical functional layers in everyday applications. These nanoscale functional materials are increasingly required to put their thermal stability and optimum performance under mechanical stress to the test. That also leads to greater demands being placed on testing technology and optical quality assurance.

The printing industry also holds the key to cutting production costs: Printing technologies with very high throughput rates ensure lower costs, but instead of the colored ink used in conventional printing, organic and printable functional materials are used. High precision and accuracy in manufacturing is essential. For example, the pressure with which the electrically conductive polymers are applied is what ultimately determines the ability to function and reliability of the final product. Great progress has been made in the last few years, but there are still a number of challenges to be met. For example, there are still no standard processes. Suitable printing techniques must be selected and optimized based on the application, material and layering. For example, gravure, inkjet, screen, offset and flexo-printing techniques can be used and combined, depending on the requirements for each layer and its structure.

Integrated techniques for mass production
Thomas Kolbusch, Vice President of Coatema, is convinced that development is clearly heading toward integrated systems. In concrete terms, that means that in addition to conventional printing techniques, more and more familiar techniques from semiconductor manufacturing will be used in the production of organic electronics in the future. Examples include nano-imprinting, laser structuring and optical lithography techniques— albeit in roll-to-roll processes. "The challenge is finding a way to precisely combine these processes and maintain the same speeds for all roll-to-roll processes and yields that are as high as possible," says Kolbusch, summing up the requirements. Integrated manufacturing is the trend against which things will be measured in the future to determine if organic electronics can succeed in mass production, even for sophisticated products.

The extremely thin layer thicknesses needed to manufacture organic solar cells are placing extremely high demands on layer precision in the longitudinal and transverse directions. Slot die technology is usually used for applications involving thin layers. The challenge is that both the die’s discharge slot and the distance between the die and the substrate must be adapted to these thinner layers. "The product is the measure of all things," emphasizes Andrea Glawe, Development Director at Kroenert. It determines what layer thickness to apply, the processing properties of the layering material, the drying and curing process and ultimately the handling of the substrate, she adds: "The 'art' is knowing both the product and the processing steps so precisely that they serve as a basis for defining the best possible coating system layout." In the process, theoretical knowledge and practical experience create an indispensible foundation that is constantly expanded by additional coating trials.

There are requirements that pertain to the automation technology, above all in the precise regulation of various processes within the machine. This increases the demands that are placed on the monitoring and control technology. Web transport and the processing units must be perfectly synchronized so that an exact web tension can be maintained. Another demanding part of the roll-to-roll technique is the vacuum zone for vapor deposition or sealing the materials. The substrate must be free of particles and transported with freedom of movement under vacuum conditions so that cables and electronics do not disturb the process. "Automation technology is a key factor when it comes to implementing processes in a reliable and cost-effective manner," asserts Lucas Wintjes, Senior Vice President, Sales and Industry Sector Management Factory Automation, Business Unit Industrial Applications at Bosch Rexroth.

Into the future
Dr. Reinhard Pfeiffer, Managing Director at Messe München, is convinced: "Organic and printed electronics is a future technology that will ultimately have an influence on all branches of industry. Research institutes and companies in all branches of industry around the world are working on printed electronics." According to Pfeiffer, this technology would give Germany and Europe a rare opportunity to once again assume a leading role in an electronics production sector. That would apply to several major branches of industry such as the chemicals, machine manufacturing, printing and packaging, logistics and consumer goods industries, just to name a few. "As a result, organic and printed electronics is very significant when it comes to securing jobs in established industries and creating new jobs in a new branch of industry."

The OE-A (Organic and Printed Electronics Association) has also recognized this trend: "Organic and printed electronics is growing at a stable rate," confirms Dr. Klaus Hecker, Managing Director of the OE-A. The facets of this technology are too diverse to be driven by a single application. The fifth edition of the OE-A's roadmap shows what is already possible with organic and printed electronics and what will be possible in the future. Its goal: to give industry, research and politics a common planning foundation. The roadmap reflects the point of view of the OE-A's members. More than 250 experts worked on the fifth edition.

The roadmap divides applications for organic and printed electronics into five sectors: organic photovoltaics, flexible displays, OLED lighting, electronics and components, and integrated smart systems. It also provides an overview of the materials and substrates that are used as well as printing technologies. The OE-A's experts have analyzed all previously existing applications and technologies and derived the industry's trends on the basis of them. They also find out what the largest challenges are. "The industry is new, but it is currently developing into its own industry. That is why it is important to overcome the ‘Red Brick Walls’ quickly to pave the way for other applications in mass production," says Hecker.

Large-area, Organic & Printed Electronics Convention

Organic and Printed Electronics Association