#2016 / Monocoque Printed Circuits

A car’s Monocoque (a French term) refers to a type of vehicle construction in which the body is integral with the chassis; basically a “skin” that supports its load by distributing tension and compression across its surface. Monocoque Structure is a technical term used in designing cars and boats. Most cars no longer use frames for structural support and crash-protection.
Similar ideas were introduced for wiring in electronic devices. More than half of flexible circuits are now designed with 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 smart phones 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 Device (MID) is a circuit technology developed and used by several circuit manufacturers over the last few decades. Progress has been made with 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 we call them 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 multi-layer construction is available.
Monocoque Printed Circuits can be a great advancement for printed circuit construction. Currently, there are not enough engineering data and design guides to move forward this 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!

Dominique K. Numakura, dnumakura@dknresearch.com
DKN Research, www.dknresearch.com

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Headlines of the week
(Please contact haverhill@dknreseach.com for further information and news.)

  1. Murata (Major device manufacturer in Japan) 6/5
    Has co-developed a new lactic fabric “PIECLEX” as the power generation material by piezo-effect with Teijin for wearable devices.
  2. Murata (Major device manufacturer in Japan) 6/9
    Has decided to terminate the manufacturing of lithium ion batteries in 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 distributers in Japan had made negative growths for the revenue of fiscal year, March 2020.
  4. Furukawa Electric (Major cable manufacturer in Japan) 6/9
    Will start the volume production of bi-polar type batteries in 2022 as the next generation energy storage device with half cost of lithium ion batteries.
  5. Mitsubishi Electric (Major electric and electronics company in Japan) 6/11
    Will invest 20 billion yens to enlarge the manufacturing capacity of power semiconductor devices. Mitsubishi will purchase the major process from Sharp in Fukuyama.
  6. Mitsubishi Electric (Major electric and electronics company in Japan) 6/15
    Has decided to close TFT- LCD panel business by June 2022. The global market price has declined too quickly.
  7. TIT (Technical college in Japan) 6/16
    Has discovered a new proton conductor that enable low temperature operation of fuel cells.
  8. Rohm (Major device manufacturer in Japan) 6/17
    Has developed a new green blue color LED with 1608 size. A new packaging resin was used to make the life 20 times longer. Wave length of the light: 505nm
  9. Hoshiden (Major device manufacturers in Japan) 6/19
    Has developed a new BLE (Bluetooth Low Energy) module “HRM3012” with high performance antenna for automobile devices.
  10. Gifu University (Japan) 6/22
    Has 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

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