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For the first time, the necessity to thermally pre-treat ubiquitously used PET substrates for printed electronics, to improve dimensional stability during manufacturing, is clearly defined. The experimental results have proven this phenomenon for both roll-to-roll (R2R) and sheet-to-sheet (S2S) processing of printed electronics. The next generation of electronics manufacturing has pushed the boundaries for low-cost, flexible, printed, and mass produced electronic components and systems. A driving force, and enabling production method, are the R2R printing presses. However, to produce electronics with increasing complexity and high yield in volume production, one must have a highly accurate process. In this article, R2R processing accuracy of printed electronics is evaluated from the point of dimensional accuracy of the flexible polyester substrate (DuPont Teijin Films’ PET Melinex ST504 with and without indium tin oxide, Melinex ST506, and Melinex PCS), precision of printing, and accuracy of layer-to-layer registration with stages that involve tension and elevated temperatures. This study has confirmed that dimensional changes during R2R processing will occur only in the first processing stage and that if a thermal pre-treatment run for the substrate is made—at identical temperature and tension of the processing stage—there is improved stability originating from a new-level strain in the crystalline PET film structure and freezing it in at the tensions and temperatures it is exposed to (i.e. 1400 μm machine direction stretching reduced to 8 μm). Furthermore, it is explained how the dimensional accuracy can be improved and reproducibly maintained in multilayer printing of electronics devices such as organic photovoltaics (OPV). These devices provide a valuable baseline of how the layer-to-layer alignment accuracy plays a crucial role in fully printed electronics devices, which lessons can be applied in all aspects of this field including hybrid systems and system fabrication involving multiple processing methods.

Stretchable electronics has attracted much interest recently because of its potential applications in the area of wearable electronics and healthcare. Highly elastic polydimethyl siloxane (PDMS) has been for decades a widely used material in prototyping purposes. It enables the realization of a variety of mechanical and optical functions besides being a substrate for other processes or applications. As a substrate, PDMS enables high stretchability and easy integration of other parts made of PDMS. In this work, we demonstrated a high-volume production of stretchable electrical interconnections on PDMS substrates. We used roll-to-roll (R2R) rotary screen printing that has been conventionally applied in high-throughput fabrication of electronics on flexible, but not stretchable, substrates. We demonstrated silver interconnects whose conductivity remains sufficient for signal transmission, for example, in sensor structures under repeated 20% strain over 100 cycles. We also demonstrated R2R compatible PDMS encapsulation of electrical interconnections that increased the strain repetition durability by a factor of 2.

This paper introduces high throughput processing of hybrid flexible RGB LED displays. Processing consists of conductive tracks printing on PET substrate, verification of printed substrate quality by specific characterization equipment and assembly of individually addressable RGB LEDs on substrate using adhesive bonding process. High throughput in manufacturing of flexible displays is achieved utilizing roll-to-roll processes in all steps of the manufacturing process. Utilization of seamless printing tool doubled printing process throughput compared to traditional printing process requiring two printing tools and steps. Implemented roll-to-roll automated electrical test equipment enabled high throughput testing and verification of printed substrate web functionality. Testing was a very important step to verify that printed wiring on the web fulfilled quality requirements for the assembly process. Required SMD components electrically bonded on substrate with R2R assembly machine by utilizing Isotropic Conductive Adhesive (ICA). In addition, Non-Conductive Adhesive (NCA) utilized to provide mechanical support of component, when flexible system bended to smaller than 20 mm radius. Dispensing process noticed to be the most time consuming process in flexible LED display manufacturing, when numerous adhesive dots applied on the substrate. In order to increase throughput in manufacturing, decrease of time used in dispensing process needed. Throughput increase by a factor of ten was possible to achieve by utilizing high speed dispensing process. Increase of more dispenser units in the dispensing process furthermore increase achievable throughput in the manufacturing process. Two meter long flexible display system demonstrator was designed, manufactured and tested based on processed flexible display element.

This paper discusses the modeling of the lifetime of printed conductors on a flexible substrate under cyclic bending. Roll-to-roll printed silver lines on a plastic film were exposed to cyclic strains accordant to the bending radii of 15, 20, and 30 mm, and their long-term electrical behavior was monitored in situ with four-point dc resistance measurements. By using 5%, 10%, and 20% increase in resistance as failure criteria, the lifetime of test populations was assessed utilizing the Weibull reliability analysis. Based on these results, the relationship between the applied strain and the lifetime was characterized and modeled by the Coffin–Manson equation. The Coffin–Manson relation accordant behavior for the lifetimes under various strains was also verified by confirming measurements with untapped bending radii with good results. As a conclusion, the lifetime of a printed conductor with known geometry and materials under cyclic bending was able to be modeled as a function of bending radius with the Coffin–Manson relation.

Novel continuous and mass customizable light-emitting 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.

Despite its potential prognostic value concurrent atrial ischemia is often overlooked in patients with acute myocardial infarction (AMI). There is no study concerning the relationship between atrial coronary circulation and dynamic PR-segment changes in patients with AMI. We evaluated dynamic PR-segment changes in 37 patients with AMI. The flow in the principal atrial coronary branches was diminished in 14 (38%) patients. Dynamic changes in the PR-segment level [median 47 (inter quartile range 19–55) μV vs. 23 (18–30) μV, P = 0.005] and PR-segment area [3.15 (1.75-3.69) nVs vs. 1.62 (1.18-2.04) nVs, P = 0.005] were significantly greater in patients with compromised than in those with normal flow in the atrial coronary branches. Our findings support the concept that atrial ischemia produces similar changes in the PR-segment as ventricular ischemia in the ST-segment. Given the possible deleterious consequences of atrial ischemia these data may have important clinical implications in evaluation of patient with AMI.

The cyclic bending reliability of printed conductors fabricated with different polymer thick film pastes is studied in this article. Three silver pastes with different properties, Asahi SW1400, Asahi LS411AW, and DuPont 5064H, were utilized to deposit test specimens on a 125-μm thick polyethylene terephthalate foil, Melinex ST506, and to investigate the paste characteristics affecting the mechanical durability of the test specimens. The main fabrication method for the traces was roll-to-roll printing with a rotary screen, but also a sheet-based screen printing process was used to compare the results between the two manufacturing techniques. The electrical behavior of the test components was monitored by measuring the DC resistance of the test samples in situ under cyclic bending in both compression and tension with about a 6 mm bending radius. The reliability of the studied test populations was assessed with the statistical Weibull analysis as the failure criterion was a 20 % increase in resistance. It was found that the conductors fabricated with the paste with the smallest silver particle size, Asahi SW1400, had the highest lifetimes. This was due to the more flexible micro-scale structure with a lower volume fraction of silver in the paste. In addition, heat-treatment during the printing process was observed to be a crucial factor from the both electrical and mechanical perspectives of the printed conductors.

A hermetic fiber pigtailed laser module utilizing passive device alignment on a low-temperature cofired ceramics (LTCC) substrate is demonstrated. The 3-D shape of the laminated and cofired ceramic substrate provides the necessary alignment structures, including grooves and cavities, for the laser-to-fiber coupling. When the laser diode chip and component tolerances are tight enough, the passive alignment allows high coupling efficiency realizations of multimode fiber pigtailed laser modules. The ceramic substrate is intrinsically hermetic and it opens up the possibility to use the substrate as an integrated part of the hermetic module package. In our concept hermetic sealing is produced by utilizing a Kovar frame, which is soldered to an LTCC substrate. The Kovar frame has a hole for a fiber feed-through and a hermetic glass-metal seal between fiber and frame is processed using a glass preform. The module can be used as a transmitter in a laser pulse time-of-flight distance sensor and in this application it can be overdriven by a factor of 10. This means that the peak optical power in the pulses can be several dozen watts. The laser chip allows this kind of overdriving, due to the fact that the duty factor in the operation is only 0.0% at 2 kHz pulsing frequency, which leads to an average power of several milliwatts. The simulated nominal coupling efficiency between the 210 mum times 1 mum stripe laser and the 200/220 mum step index fiber (NA = 0.22) was 0.65. The measured coupling efficiency of the hermetically sealed prototypes varied from 0.14 to 0.64, where the average was 0.39. A leak rate of 1 times 10-7 . .. 8 times 10-7 [atm times cm3/s] was measured in the helium leak tests of the final operational prototypes, when the modules were tested according to MIL-STD-883F method 1014.9 specification. The rather high leak rate is mainly due to the helium absorbed by the fiber polymer buffer layer and rubber guard tube in the pressurization process. The leak rate for the dummy modules using a buffer stripped fiber without a rubber guard tube was 3 times 10-9 . .. 1 times 10-8 [atm times cm3/s]. The maximum allowed leak rate for this size of hermetic module is 1 times 10-7 [atm times cm3/s]. The background helium level before and after the tests was less than 3 times 10-10 [atm times cm3/s]. Measurements proved that the manufacturing procedure is capable of producing hermetic fiber pigtailed laser modules.

Freedom of design that was introduced as organic photovoltaic (OPV) modules were fabricated by printing. As proof-of-concept, we show OPV leaf fabrication in A5 size using gravure and rotary screen printing processes for the main active layers of the OPV structure. These printing methods allow direct printing of any kind of arbitrary, two-dimensional shapes including patterning of the electric contacts thus post-patterning stages are not needed. Fabrication of custom-shaped OPV modules requires detailed information about the technical boundaries set by the manufacturing process and materials which in turn influence the layout design and R2R upscaling. In this paper, we show custom-shaped OPV modules, patterned directly in a shape of a tree leaf with an overall size of 110 cm2 and an active area of 50 cm2 providing a power conversion efficiency of 2.0% and maximum power of 98 mW.

Autonomous systems are pursued in automotive and signage applications due to easy installation and achieved energy savings. In addition, reduction of cabling decreases system weight, which is especially pursued in automotive applications due to the decreased fuel consumption. Naturally, autonomous systems require some kind of energy harvesting and energy storing systems. In order to achieve required autonomy operation time of over 15 hours, four flexible Li-Ion batteries of 1200 mAh total capacity in automotive demonstrator and four flexible Li-Ion batteries of 3200 mAh total capacity in signage demonstrator were required. The dimensions of batteries were 295 mm × 29 mm and 295 mm × 119 mm. The energy harvesting for autonomous operation was based on flexible commercially available amorphous silicon solar cells, types MP3-25 and MPT6-150 manufactured by Power Film. The dimensions of the solar cells were 114 mm × 29 mm and 114 mm × 150 mm. The pursued autonomy time of demonstrators resulted to a large surface area requirement for the backplane substrates. The dimensions of the assembled automotive demonstrator were 2400 mm × 35 mm × 0.95 mm and the dimensions of the assembled signage demonstrator were 2550 mm × 144 mm × 0.95 mm. The large size of both the components and the substrates produced challenges for assembly and bonding processes. As the bonding method hot bar bonding or oven curing were used, the experimental procedure being compatible with the guidelines of the material suppliers. Daisy chain test structures were used to study the interconnections between the foils. Thermal humidity testing at 85°C/85%RH and thermal cycling between −40….+85°C were used as the environmental tests for the test structures processed before final selection of the bonding materials and processes for demonstrators manufacturing. Both manufactured demonstrators were operational after assembly and bonding processes. The energy produced by the solar cells was guided to the Li-Ion batteries by a specific charge regulator. Batteries were able to supply power to the automotive and signage LED elements so that the systems autonomous operation was successfully demonstrated.

An infrared (IR) temperature measurement system consists of a sensor module and electronics as well as an optomechanical system that guides IR radiation onto the sensor. The geometry and emissivity of the optomechanics can affect the temperature reading. We show how the traditional optomechanical design of the IR temperature measuring systems produce inaccurate results when used in handheld mobile devices. When the mobile device is not thermally stable and the measured targets are significantly colder than the device, the measurement error can be several degrees. Our new optomechanical design was optimised for handheld mobile use, and its optics performance was modelled and verified by prototyping. The temperature measurement and sensor calibration is based on only two signals, namely the thermopile and thermistor voltages of the IR detector. This is a very attractive method in high-volume consumer products because no additional components are needed to improve the measurement repeatability. The attainable repeatability of the implemented IR temperature sensor on a correct transferred calibration curve was better than ±0.5 °C in an operational temperature range from +13 to +49 °C and target range from +10 to +90 °C.

An infrared (IR) temperature measurement system consists of not only a sensor module and electronics, but also an optomechanical system that guides IR radiation onto the sensor. The geometry and emissivity of the parts affects the reading, if the detector sees not only the target but parts of the measuring system itself. In normal industrial applications, the optics is designed so that the surfaces stabilize to the same temperature as the sensor. This allows the error caused by the device temperature to be easily calibrated away. The correction is valid for stationary conditions and usually near the calibration temperature, which is typically at room temperature. However, we show that if the sensor is embedded into a mobile (hand-held) device which has heat sources, such as power electronics, the normal conditions are no longer valid and the calibration fails. In order to improve infrared temperature sensing for mobile devices, the optics concept was studied and detailed design was performed. In addition, the optics performance was modelled and verified by measurement sensor prototyping. A calibration procedure noticing operational temperature variations was applied. The repeatability of the implemented IR temperature sensor using on a correct transferred calibration curve was better than plusmn0.5degC in an operational temperature range from +12.6 to +49.3degC and target range from +10 to +90degC.

A hermetic fibre pigtailed laser module utilizing passive device alignment on a low temperature co-fired ceramics (LTCC) substrate is demonstrated. The 3-dimensional shape of the laminated and fired ceramic substrate provides the necessary alignment structures including holes, grooves and cavities for the laser to fibre coupling. The achieved passive alignment accuracy allows high coupling efficiency realizations of multi-mode fibre pigtailed laser modules. The ceramic substrate is intrinsically hermetic and it opens up a possibility to produce cost efficient hermetic packaging. In our concept hermetic sealing is produced by utilizing Kovar frame, which is soldered to an LTCC substrate. Kovar frame has a hole for fibre feed-trough and a hermetic glass-metal sealing between fibre and frame is processed using glass preform. The heart of the module is a power laser diode chip, which can produce several watts of continuous power. The module, however, can be finally used as a transmitter in a laser pulse time-of-flight distance sensor and in this application it can be overdriven by a factor of 10. This means that the peak optical power in the pulses can be several tens of watts. The laser chip allows this kind of overdriving due to the fact that the duty factor in the operation is only 0.0001 at 2 kHz pulsing frequency. Optical coupling efficiency of the multi-mode laser system was simulated using optical systems simulation software. The nominal coupling efficiency between 210 μm x 1μm stripe laser and 200/220 μm step index fibre (NA=0.22) was 0.65. The simulated coupling efficiency was verified by prototype realization and characterization. The measured average coupling efficiency of the hermetically sealed prototypes was 0.39. The coupling efficiencies of prototypes varied from 0.14 to 0.64. Leak rate of 1 x 10-7 [atm x cm3/s] was measured in the helium leak tests for the final prototype module, when the module was tested according to MIL-STD-883D method 1014.9 specification. Leak rate for the module using a buffer stripper fibre without a rubber guard tube was 3 x 10-9 [atm x cm3/s]. The background helium level before and after the tests was less than 3 x 10-10 [atm x cm3/s]. This clearly higher leak rate in the final module leak measurement is mainly due to the absorbed helium to the fibre polymer buffer layer and rubber guard tube in the pressurization process. Measurements show that the implemented module is hermetic. Cost-of-ownership modelling was performed starting from low production volume up to production of 10 million good modules per year. Module production cost was estimated through COO modelling. Modelling forecasted that the module production can be lower than 10 EUR in high volume production.

In photonic module integration, optoelectronic chips, micro-optical elements and integrated circuits are integrated into functional components, sub-assemblies, modules and systems. The building blocks of the photonicsystem must be fabricated by the use of cost-efficient, reproducible, well-established, high-volume manufacturing technologies. The reliability of the system as well as the tolerances of device alignment are key issue in the integration. We have developed a Low Temperature Co-fired Ceramics (LTCC) toolbox for photonic integration. The primary aim was to process co-fired 3D structures, such as, grooves, cavities, holes, bumps and alignment fiducials for the passive alignment of photonic devices. LTCC provides means for full 3D integration. The tolerances of the alignment structures are typically ±5µm and in some specific cases ±2µm. LTCC structures provide means for the passive alignment of multimode fiber, for example. With Monte-Carlo tolerancing tools, we can simulate and optimize the performance of the system and estimate manufacturing yield in volume production. Thermal management by the use of thermal vias is a well-established technique; liquid cooling channels in the LTCC substrate provide efficient means for high-power laser cooling. LTCC providesinherently hermetic substrate allowing the possibility for hermetic encapsulation. High-speed ICs as well as millimeter-wave circuits can easily be integrated into the LTCC substrate. Novel materials allow the fabrication of advanced systems, especially, for millimeter-wave operation.