DKN Research develops many types of unique electronic circuits. Some of these products in our portfolio include ultra thin conductor circuits as small as 0.2 microns, metal free circuits and circuits up to 20 meters long. Our staff fields many inquiries for packaging of new electronic devices. Lately, there is a lot of interest in transparent flexible circuits. The increase in interest is due to the recent market expansion of display and optical devices.

One example of this is touchscreen displays for tablet PCs and smartphones. When Apple launched the iPod Touch, touchscreen displays became the benchmark for the industry. The flexible circuits found inside must be transparent so the user can see the LCD panel. Unfortunately, the most popular substrate material to use in flexible circuits is polyimide film because it is brown in color and is not optically transparent. Circuit manufacturers use PET films instead of polyimide films because its heat resistance is remarkably lower compared to polyimide film. Circuit manufacturers had to develop a low-temperature processes using the correct materials to make this a success. After many trials, PET films are the standard to use as the substrate material for touch screen displays in mobile devices.

Many applications for industrial and aerospace devices demand both transparency and heat resistance. Up until now, this was not possible. Recently, a Japanese plastic manufacturer developed a process using transparent polyimide film as the main substrate for flex circuits in a volume application setting. This will remove a technological barrier for heat resistance and is a huge progress for transparent circuits.

Many are asking if transparent flexible circuits are practical on a commercial scale. The answer could be yes if we push through one more barrier - transparent conductor. Copper foils are the major conductor material for printed circuit boards, but they are not transparent so they are eliminated. Indium tin oxide (ITO) was used as an alternative transparent conductor for the most of the display devices, but it can be sputtered at relatively low temperatures. Its conductivity is much lower compared with metallic copper, and many researchers are trying to develop conductive organic molecules for this purpose. Other researchers are considering the use of carbon nano tubes or graphene as the transparent conductor, unfortunately their conductivities are not much greater than ITO and other problems need to be addressed before any commercial application is considered. Currently, silver nano wire and thin metallic mesh screen may be the key even though the row materials are not transparent. Creating appropriate opening turns the materials transparent with higher conductivities. This is not the perfect solution, but they are practical. That’s why I am optimistic that transparent flexible circuits are practical on a commercial scale.

A few smaller challenges that need to be addressed center around cover materials and adhesive materials. These secondary materials can be made transparent with a few minor changes based on their current performances.

We can now create several types of heat resistant transparent flexible circuits by using a few different combinations. The only thing I can’t tell you is how much all of this will cost - the cost structures for most of the materials have not been determined.

Dominique K. Numakura, This email address is being protected from spambots. You need JavaScript enabled to view it.

DKN Research, www.dknresearchllc.com

DKN Research Newsletter #1522 July 19, 2015 (Micro Electronics & Packaging, www.dknresearchllc.com)

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Headlines of the Week

1. Yaskawa Electric commercialized a spot welding robot MOTOMAN-VS100 for assembling automobiles. It has seven rotating modes.

2. Fuji Electric rolled out a steam generation heat pipe. It can utilize low temperature waste water.

3. Hitachi started volume production of the one-chip distortion sensor utilizing a metal-bonding technology for automobile applications.

4. AIST developed an ultra high-density capacitor device using mono-layer carbon nano tube. The size can be one thousandth compared to aluminum capacitor.

5. Toshiba developed a multilayer magnetic memory system. It will enlarge the memory capacity of hard disc drives significantly.

6. Mitsubishi Electric commercialized a new heavy duty robot series. The largest robot can handle 70kg.

7. AIST has been codeveloping a hydrogen base power generation system using aluminum waste materials.

8. Mitsubishi Motors agreed to start commercial base field test of the electric power storage system with French companies. The test will be conducted in Paris, France.

9. Daikin started field tests of a micro hydroelectric power generation system that utilizes the power of city water and sewerage.

10. Rohm developed the world smallest (2mm x 2mm) pressure sensor “BM1385GLV” with a high precision for mobile devices and wearable devices.

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