FLEX007

Flex-Oct2018

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56 FLEX007 MAGAZINE I OCTOBER 2018 ters—such as polyethylene terephthalate (PET) and polyethylene naphthenate (PEN), rubber- like material (thermoplastic polyurethane or TPU), and even paper—are known substrates for printed electronics. The low costs of these materials immediately show the second advan- tage of printed electronics. A third benefit of printed electronics is the ability to change the form factor of the PCB. Foils are easy to shape into the desired form by bending, rolling, cutting, and laminating. In this way, the electronics can be integrated eas- ily into examples like clothing, building, and on-body applications. The prints can also be seamless, effectively with no beginning and no end, so that the size of the PCB is limited only by the length and width of the roll. LED foils are printed at the Holst Centre with a length of 300 m and a width of 30 cm. The LED foils have a pitch of 5 cm and are used as a wallpaper lighting source for indoor applications. The Technology of Printed Electronics PCB production is a well-established indus- try following highly standardized procedures and design rules, resulting in a robust and reliable hybrid manufacturing process. Replacing substrates, such as polyimide and FR-4 with a flexible film like PET, will disrupt the industry. Currently, printed electronics can realize conductivity of 10–20% bulk sil - ver, and a feature size and pitch of 150/150 microns at industry-proven process condi- tions. In research, conductivity 20–40% of bulk silver, stretchable inks, and feature size/pitch of 20/20 microns have already been reported. More and more electronic functionalities can be printed. Examples include resistors, temper- ature and pressure sensors, and haptic func- tionalities. Additional functionalities—such as microcontrollers, batteries, and capacitors— can be integrated on the flexible circuit using traditional pick-and-place technology. Inter- connection is usually made with isotropic or anisotropic conductive adhesives that may be deposited by dispensing or printing. Assembly of foil-like components on a foil-like substrate will be realized in the near future. Examples of these components are OLEDs, TFT chips, and foil-based batteries. Figure 2: Roll-to-roll printed circuits on film.

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