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EPTE Newsletter: Monocoque Printed Circuits, Part 3

When speaking of cars, the term “monocoque” (a French word) refers to a specific type of construction. Monocoque structural techniques are used in a wide-ranging variety of products, including automobiles, boats, other types of vehicles, skis, and much more. Most cars no longer use the frame alone for structural support and crash protection.

Similar ideas were introduced for wiring in electronic devices. More than half of flexible circuits are now designed as 3D wiring for tight spaces in small electronic devices. Rigid printed circuits and wire harnesses were not adequate, so flexible circuits are options for 3D wiring in smartphones and tablet PCs. The relatively high cost of flexible circuits is an issue for device manufacturers; they are considering alternatives for building electronic circuits on plastic housing with or without framing. Once a new 3D wiring technology is available, they can significantly reduce wiring space and assembling costs.

Molded interconnect devices (MIDs) are a circuit technology developed and used by several circuit manufacturers over the last few decades. Progress has been made in creating a few 3D conductive circuits using an electroless plating process on molded plastic parts for electric connections. Unfortunately, the plating process is not very flexible and limits its use in many applications.

A set of thick-film processes were successfully developed in Japan and Taiwan to create 3D wiring using a standard screen-printing process with special conductive ink when building 3D circuits. The process is very simple. First, a silver ink with high flexibility and stiffness is screen-printed on thermal plastic sheets (PET and acrylic resin). The screen-printing process and baking processes are repeated for multilayer constructions. Next, a thermal forming process is used to make 3D wiring. The 3D circuit could be held when the circuit is removed from the forming die and cooled down. They have circuit capabilities and mechanical capabilities in their structures. That is why they are called monocoque printed circuits.

The circuits’ thickness is less than 30 microns for single layer conductors. The space necessary for wiring is almost zero and eliminates flexible circuits. There can be options for substrate and conductor materials, and double-layer or multilayer construction is available.

Monocoque printed circuits could be a great advancement for printed circuit construction. However, there are currently not enough engineering data and design guides to move forward with this technology. Continuous trials are necessary to establish references, but circuit manufacturers must collaborate with end-users for their valuable input. We welcome all comments!

Editor’s Note: Dominique Numakura first covered monocoque printed circuits in a column from PCB007 Magazine in May 2019, as well as an update in September 2019.

Headlines

1. Murata (device manufacturer in Japan) 6/5

Co-developed a new lactic fabric PIECLEX as a power-generation material with Teijin for wearable devices by the piezoelectric effect.

2. Murata (device manufacturer in Japan) 6/9

Decided to terminate the manufacturing of lithium-ion batteries in its Kanuma Plant by March 2022. The manufacturing will be transferred to Motomiya Plant.

3. EE Times (industrial media in Japan) 6/10

More than half of major semiconductor distributors in Japan made negative growths for the revenue of fiscal year ending March 2020.

4. Furukawa Electric (cable manufacturer in Japan) 6/9

Will start the volume production of bipolar-type batteries in 2022 as next-generation energy storage devices with half the cost of lithium-ion batteries.

5. Mitsubishi Electric (electric and electronics company in Japan) 6/11

Will invest 20 billion yen to expand the manufacturing capacity of power semiconductor devices. Mitsubishi will purchase the major process from Sharp in Fukuyama.

6. Mitsubishi Electric (electric and electronics company in Japan) 6/15

Decided to close TFT- LCD panel business by June 2022 because the global market price had declined too quickly.

7. TIT (technical college in Japan) 6/16

Discovered a new proton conductor that enables the low-temperature operation of fuel cells.

8. Rohm (device manufacturer in Japan) 6/17

Developed a new green-blue color LED with a 1608 size. A new packaging resin was used to make the life 20 times longer (wavelength of the light: 505 nm).

9. Hoshiden (device manufacturers in Japan) 6/19

Developed a new Bluetooth low-energy (BLE) module “HRM3012” with a high-performance antenna for automobile devices.

10. Gifu University (Japan) 6/22

Developed a new compact antenna for next-generation telecommunication systems with tera-Hz bands after 5G and 6G (1.36 x 1.36 x 1.72 mm).

Dominique K. Numakura is the managing director of DKN Research LLC. Contact haverhill@dknreseach.com for further information and news.