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EPTE Newsletter: Transparent Circuits Gaining in Popularity

Transparent printed circuits were a popular item at the JPCA Show 2016. Polyethylene terephthalate (PET) use to be the dominant material used for transparent substrates in optical circuits and devices and generated a huge amount of sales from touch screen panels. Many engineers and designers still searched for other heat-resistant and transparent substrate materials because PET's heat-resistance was not robust enough for the standard connection processes that use soldering and wire bonding. Polyimide films have a superior heat-resistant tolerance as well as favorable electrical and mechanical properties, but their colors are brown, making transparencies challenging.

Last year, at the JPCA Show 2015, one material company unveiled a commercialized transparent polyimide film. Since then, a number of related products and technologies were born. Many companies are expecting significant business opportunities from transparent and heat resistant printed circuits. Here at DKN Research, we are very familiar with these technologies—listed below are a few details we would like to share:

There are at least five material manufacturers that developed transparent and heat-resistant plastic films. These manufacturers will not disclose details about the chemistries of their plastic films. Most of them are polyimide-base resins, but they have different molecular structures compared with traditional polyimide films such as Kapton or U-pilex. The 25-micron thick films are 80–90% transparent, and their mechanical and chemical properties are slightly different, but their electrical properties are similar. Three companies developed copper laminates with transparent films; DKN Research is one of them. A few manufacturers are considering laminating copper foils using transparent glues, but the adhesive layers could reduce the transparency. They are forced to consider employing a different metallization processes without the use of glue. There will definitely be a tradeoff between transparency and the bond strength of the conductors.

DKN Research is one of a handful of circuit and electronic device manufacturers that developed transparent flexible circuits for single-layer and double-layer use. Circuit manufacturers are considering the use of transparent cover layers for circuits. This can be accomplished two ways—film based or screen-printable based. Both ways do not have a better transparency than base substrate layers. A few circuit manufacturers as well as DKN Research are considering transparent conductors. Unfortunately, there will be tradeoff between transparency and conductivity.

Currently, there are many R&D projects on schedule to be released soon. Based on these technical advancements, many device companies will adopt the new transparent and heat resistant circuits to be used mostly in optical and sensor devices applications designed for medical and scientific equipment.

I read many inquiries at DKN Research. There is a significant need for transparent circuits, but I think we are a couple of years away from transparent and heat resistant circuits becoming a meaningful product in our industry. However, technology is on a knowledge-doubling curve; I believe there will be a relevant market for these circuits in the near future.

Headlines of the week

1. Rohm (Major device supplier in Japan) 6/21

Has developed a new sulfur resistant chip resistors “SFR Series” for automobile devices. They keep the performances under SO2 rich atmosphere.

2. Showa Denko (Major chemical company in Japan) 6/16

Will expand the manufacturing capacity of carbon cathode materials for lithium ion batteries to catch up the growing demand in automobile industry.

3. Murata (Major component supplier in Japan) 6/23

Has been expanding the product lines of laminate type energy storage devices. They can be charged in short time.

4. Kyushu University (Japan) 6/28

Has discovered a near infrared ray emission process of carbon nano tube. It does not need rare metals. The process could be valuable for bio devices.

5. AIST (Major R&D organization in Japan) 6/27

Has developed a new thermometer that works at 1000°C area with a high accuracy of +/- 0.001°C.

6. Kyocera (Major electronics company in Japan) 7/4

Has released a new compact BTB connector series “5861” with 0.6 mm height and 0.35 mm pitch.

7. Murata (Major component supplier in Japan) 7/1

Has commercialized the industry first ceramic base capacitor with 10 micro Farads.

Size: 3.2 x 2.5 mm.

8. NEC (Major electronics company in Japan) 6/30

Has developed a new “nano-brush” from carbon nano-horn molecules. It has excellent properties as the core material of the IoT devices.

9. AIST (Major R&D organization in Japan) 7/5

Has co-developed a new simple process to grow carbon nano tube on the surface of 3D things in typical atmospheric circumstances.

10. JST (Major R&D organization in Japan) 7/4

Has developed a new photosensitive glue. It keeps good bond strength at 100°C, but it will be peeled off by UV irradiation.

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