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Printed Electronics World
Posted on July 25, 2017 by  & 

Toppan Forms develops ITO replacement using silver salt ink

Digital Hybrid Company Toppan Forms Co Ltd has developed a technology for forming printed micro wires, which enables a wire width of 4μm (micrometers) that is almost invisible to the naked eye. The company has established this technology by combining a conductive ink for micro wiring (silver salt ink) and a corresponding printing process technology that enables circuits without the use of rare metal. The new technology can be used for transparent electrodes for touch sensor panels, wearable sensors, sensors for the Internet of Things and similar devices.
In the expanding market of electronic components for smartphones and similar devices, there is growing demand for higher performance, smaller dimensions, and new functions. This has made it necessary to miniatuarize the circuit wires of electronic components. The traditional method used for forming micro wires is the photolithographic method, which applies photographic development technologies. This method has problems including a troublesome manufacturing process, a high capital investment, a significant loss of wiring materials in the manufacturing process, and the generation of an environmentally unfriendly waste liquid. In response, the market is increasingly focused on an environmentally friendly technology for forming micro wiring that enables the manufacturing process to be simplified, and wiring materials to be used only for parts where they need to be used. While wires that could be formed using conventional printing technologies were around 10μm in width on the practical level, the new technology permits the formation of wires of just 4μm in width with continuous printing on the practical level.
Application examples of the technology
Micro wires that are 4μm wide are almost invisible to the naked eye, enabling the wires to be made virtually transparent. An application example of such wires is transparent electrodes for touch sensor panels. A common material of transparent electrode is indium tin oxide (ITO), a transparent metallic oxide. However, this material has problems with supply stability and cost because indium is a rare metal. ITO also makes it difficult to use base materials with low heat resistance because high heat is generated when an ITO film is formed.
The conductive printing ink Toppan Forms has developed this time enables micro wires to be formed in a temperature range where films for plastic base materials can be used, thanks to the composition of the silver ink and the process technology for printing micro wires. This enables the use of plastic base materials with lower heat resistance, and at the same time makes the wires transparent.
This technology also permits other applications. For example, the thin wires enable the downsizing of electronic components. The technology can also be applied to wearable devices because it permits wiring on films. It also enables fine meshes to be formed, to create electromagnetic shields. In addition, while electronic equipment using silver wires generally has a risk of electrochemical migration, the ink Toppan Forms has developed has widespread application because it has resistance to electrochemical migration on the practical level.
1. Capable of forming micro wires (width: 4μm) by means of printing
2. The new printing ink permits continuous printing on a practical level
3. Also permits wiring on thinner films (with thickness of around 100nm), with superior conductivity
(volume resistivity: 7μΩ-cm)
(Reference: Volume resistivity of ITO is 150 to 300μΩ-cm.)
4. Capable of forming wires on plastic base materials with low heat resistance (such as
5. Resistant to electrochemical migration, a risk involved in silver wiring, on a practical level
Future development
Toppan Forms will proactively seek to tie up with other companies to sell the printing ink and commercialize the technology for widespread application. In doing so, it aims to develop diverse applications and develop the business.
Source and top image: Toppan Forms Co Ltd
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