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The seamless integration of electronics into flexible, curved, and even stretchable surfaces is being requested for several markets, such as automotive (dashboards, lighting, sensors), smart buildings (lighting facades, air quality, solar panels), medical (health patches, X-ray, analysis), and smart clothing (position tracking, sports). The requirement for products that are light, take up less space, conformable, and easily integrated into an existing design will result in an improved user interface. Additionally, the product should be robust from a cost-effective process consuming less material, and the technology should be consistent with the Internet of Things (IoT) roadmap.
The Printed Electronics Concept
Printed electronics deliver smart surfaces for applications by creating printed circuits on polymer films and utilizing traditional graphical printing techniques, such as screen printing and inkjet printing, to create the circuitry on foils in sheet or roll form.
An obvious advantage of printing electronics is the speed that can be achieved. For example, there is roll-to-roll screen printing equipment at the Holst Centre that runs at a maximum speed of 60 metres per minute, creating seamless circuits directly onto a roll (Figures 1 and 2). Photonic sintering of the metal ink allows high operating speeds to be maintained at a controlled temperature of approximately 130°C to prevent the foils from melting. In combination with roll-to-roll printing, pick-and-place assembly technology can place electrical components on the roll. Conductive adhesives are usually used as interconnects.
Crossovers and vias can be printed by alternating conducting and dielectric layers, which can maintain a PCB-like structure, only now on a roll. All polymer foil materials are suitable substrates for printed electronics. Polyes ters—such as polyethylene terephthalate (PET) and polyethylene naphthenate (PEN), rubberlike material (thermoplastic polyurethane or TPU), and even paper—are known substrates for printed electronics. The low costs of these materials immediately show the second advantage 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 easily 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.
To read the full version of this article which originally appeared in the October 2018 issue of Flex007 Magazine, click here.
