Novel continuous and mass customizable lightemitting diode (LED) lighting foil system, capable to produce adequate lighting levels for general lighting, was designed, processed, and characterized. Lighting element substrate was processed by roll-to-roll (R2R) printing using silver ink and automatic bonding of LEDs and current regulators on polyethylene terephthalate (PET) substrate using isotropic conductive adhesive (ICA). Demonstrator consisting of two basic lighting elements contained 98 LEDs and produced 860 lm when running with 25 mA operational current through the LEDs when using total electrical driving power of 8.4 W. Measured power conversion efficiency of the demonstrator was 31 % and efficacy 102 lm/W. Element produced 460 lx illumination level measured by an illumination level meter at element's central axis at distance of 1 m. At a distance of 2 m, illumination level was 110 lx, respectively. Temperature measurements with T3Ster thermal characterization instrument showed that when driving LED with maximum nominal driving current of 100 mA, LED junction temperature was about 120°C, when lighting element was in air in room temperature. Accelerated environmental stress tests consisting of 500 cycles from −40 … +80°C in aging oven and 1000 h in +60°C/95 % RH climate chamber were performed to test samples without any failures. In addition, over 700 bending cycles using 20 mm bending radius were performed to test samples without any failures, so bonding of LEDs were shown reliable according to these tests. Achieved results proved that thin, flexible, and large area high luminous flux lighting elements and systems can be processed based on plastic foil manufactured using R2R silver ink printing and R2R automatic bonding of LEDs and regulator components using ICA on that foil.

In this case study, the possibilities of hybrid integration of printed and flexible electronics in combination with conventional electronic components to create new types of product concepts is demonstrated. The final result is a personal activity meter demonstrator, which is realized by utilizing various flexible electronics manufacturing and integration techniques. Roll-to-roll printing was used to print the electronic backplane as well as co-planar electrochromic (EC) display. A pick-and-place assembled microcontroller unit and accelerometer, together with passive components, provided the brains for the system. Injection molding was then utilized to create a structural electronics system including an EC display. To validate the feasibility and scalability of the processes used, 100 pieces of the personal activity meter were fabricated. Modeling with continuum computational fluid dynamics and numerical heat transfer, using the high-performance finite volume method, showed that high filling pressure and shear-stress are the key factors causing broken devices. The stability of the devices in harsh environmental conditions as well as in bending seem to be slightly improved in the over molded samples. INDEX TERMS Electrochromic displays, injection molding, hybrid integration, printed electronics, structural electronics. TERHO KOLOLUOMA received the Ph.D. degree in chemistry from the University of Oulu in 2003. From 1998 to 1999, he was with the University of Oulu having a responsibility on fabrication and characterization of solgel-based materials. From 1999 to 2003, he was with VTT Electronics for developing new materials for optoelectronic applications. During that period, he started the first experiments in the area of roll-to-roll printed electronics and optoelectronics and started to lead various research project in that field. After finishing his Ph.D. thesis in 2003, he started as a Senior Scientist focusing on development of printed electronics components and technologies, and since 2010, he has a Principal Scientist. From 2013 to 2015, he was with National Research Council Canada, he is currently a Research Team Leader of printed electronics processing team with VTT. His main research topic is printable optics and electronics. Of his special interests are novel materials for printed electronics and materials-process interface.

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Flexible and stretchable electronics present opportunities for transition from rigid bulky devices to soft and conformal systems. However, such technology requires mechanical design and integration strategies to enhance robustness and form factor. In addition, scalable and reliable fabrication pathways are needed to facilitate the high volume manufacturing required to satisfy a growing market demand. This report describes recent advances in design, manufacture, and reliability of flexible and stretchable electronics technology. Flexible concept devices for physiological monitoring are introduced, before discussion of high throughput fabrication of stretchable electronics, then hybrid integration of conventional rigid components on stretchable carrier substrates with an emphasis on a need for further developments in device reliability testing procedures. Finally, consideration is given to transition options for more eco-conscious device constituents. These cases progress flexible and stretchable electronics towards robust, fully integrated, unobtrusive devices incorporating sustainable components.