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EPTE Newsletter: Exotic Materials for Flexible Circuits

Wearable technology is common in the electronics industry and is expected to be a profitable category for the next generation of electronics. An Amazon search for wearable technology leads to 30,000 results. Flexible circuits are the most significant packaging materials for wearable devices including medical and healthcare devices.

R&D teams are considering exotic materials for flexible electronics. What are exotic materials? Currently, polyimide film is the major dielectric material, and copper foil is the primary conductor material for flexible circuits due to the heat resistance when soldering.

DuPont’s Kapton film evolved into the de facto standard for the base and coverlay film. New suppliers had to improve dimensional stabilities, higher flexing endurance, smaller gas and moisture permeability, stretchability, and more to develop alternative substrate materials to enter the flex circuit market.

R&D had to think outside of the box when developing the basic properties for substrate materials earmarked for wearable technology. Things that needed to be addressed included moisture absorption, gas permeability, transparent, elasticity, etc. There are fundamental conflicts between these requirements, and one material did not meet all of these requirements.

Fortunately, there were many traditional materials available to use as the exotic materials. Here are some examples:

• Gas permeability: paper, cloth, and gaze
• Elasticity: cloth, urethane rubber, and silicone rubber
• Moisture absorption: paper and cloth
• Transparency: transparent polyimide, PEEK, and fluoropolymer

These exotic materials are not readily available without metallization as the flexible substrate for flex circuits; appropriate metallization processes are required. DKN Research has introduced several sets of sputtering and chemical treatment processes, printing processes for conductive inks, and electroless and electrical plating processes.

Appropriate combinations of the processes can build a preferred thickness of metallic layers on these thin exotic materials. Now, traditional flexible circuit manufacturers can build wearable devices to interact with the human body (worn on the body as an implant or accessory). DKN Research is also available to help with the challenges with these new exotic materials.

Headlines

1. Maxell (Electronics material supplier in Japan) 11/12
Developed a new disposable flexible primary battery without toxic materials for the portable medical and healthcare devices.

2. Murata (Device supplier in Japan) 11/13
Invested 14 billion yen for the new manufacturing plant of MCLL in China to cover the growing demands.

3. Alps Electric (Device manufacturer in Japan) 11/13
Completed the construction of the second manufacturing building in the Osaki Plant with a 1-MW solar power generator module.

4. Nippon Seiki (Auto device manufacturer in Japan) 11/13
Developed a new reliable 3D sensor produced by a MEMS process for high frequency up to 8-kHz vibration.

5. Hamamatsu Photonics (Photo device supplier in Japan) 11/16
Developed a new four-channel pulse laser diode for the LiDAR modules of auto car drive systems.

6. Panasonic (Electronics company in Japan) 11/19
Unveiled the new platform of the 48-V base powertrain system “ePowertrain” for compact size electric vehicles.

7. Mitsubishi Electric (Electric and electronics company in Japan) 11/19
Made a prototype model of a wideband image sensor that covers visible ray to a 1,000-micrometer (terahertz) band.

8. Kyocera (Electronic device supplier in Japan) 11/19
Developed a revolutionary small antenna device “Amcenna” for a 2.4-GHz band that will be valuable for IoT and healthcare devices.

9. NEC (Electronics company in Japan) 11/20
Unveiled a new two-dimensional flexible pressure sensor sheet produced by a thick-film printing process.

10. Screen (Manufacturing equipment supplier in Japan) 11/20
Built a new plant building CS-2 in Hikone, Shiga Prefecture, for the next generation of flat panel displays, especially for flexible displays.

11. Yano Market Research (Market research company in Japan) 11/21
Forecasted the market size of lithium-ion batteries for automobile use to be 129.2 GWh by 2020.

Dominique K. Numakura is the managing director of DKN Research LLC.