In a functional eye, the iris controls the pupil diameter to regulate the exposure of the retina. While iris deficiencies such as aniridia or leiomyoma can be mitigated with fixed or adaptive artificial irises [1] and adaptive transparency glasses exist to alleviate this situation, they do not mimic the normal functionality of the natural iris. To address this, a fully encapsulated, self-contained artificial iris embedded in a smart contact lens is proposed. A control ASIC is developed in 0.18 μm 16 V BCD TSMC with typ. 1.9 μw current consumption from 3 V supply voltage at office light condition.

Within our internal FITEP technology platform (FITEP: Flexible Implantable Thin Electronic Package), a novel implantable packaging technology is under development in order to realize a very small, flexible, biomimetic package for electronic implants. This new platform enables a radical miniaturization of the final implanted device, which opens many new possibilities for the medical world, since it will be possible to insert electronic sensors in very small locations, such as arteries, nerves, glands,... The device encapsulation consists of a multilayer of biocompatible polymers and ultrathin ceramic diffusion barriers deposited using ALD techniques (ALD: atomic layer deposition) in order to fabricate a very thin and flexible but also highly hermetic device packaging. Concerning the selection of biocompatible polymers, polyimide can offer a profound mechanical support for the various device components, while Parylene with its excellent step coverage creates a highly conformal coating surrounding all components. Hermeticity can be realized by the use of ultrathin ceramic ALD layers such as Al2O3 and HfO2. An optimized ALD process will result in layers from very high quality with very good step coverage. As such, selected ALD layers of only a few tens of nm thick, can exhibit very low Water Vapor Transmission Rates (WVTR), making these ALD materials ideal as ultrathin diffusion barriers. The tested polyimide/ALD stack proved to be a very hermetic enclosure: copper patterns protected with the polyimide/ALD stack are still in perfect condition after more than 2 years of immersion in saline at 60 °C (test is still ongoing), while Cu patterns protected by the polyimide stack without ALD barriers showed first signs of damage already after 6 weeks exposure to saline. Platinum and gold are best suited for metallization of implanted electronics, but these noble metals do not adhere easily to polymers, hence dedicated measures to promote metal-polymer adhesion are essential. The FITEP platform is applied on a Si-probe for implantation in the peripheral nerves, consisting of a CMOS chip with recording and stimulation electrodes [Op de Beeck, M. 2017]. The chip is thinned down to 35um and packaged using polyimide and ALD multi-stacks, resulting in a 75um thin fully encapsulated chip, optimized to reduce the Foreign Body Reaction to obtain optimum electrode-nerve contact. Flexible interconnects are fabricated using gold and platinum sandwiched between polymers and ALD layers. For optimal charge injection, iridium oxide is used as electrode material. After this hermetic FITEP-based chip encapsulation, the CMOS chip is still fully functional, which was tested dry (in air) as well as during submersion in saline. First acute in vivo stimulation tests have shown good electrode stimulation capabilities. Mechanical bending tests on long 5um thick gold interconnects are performed, showing that even after up to 1.5 million bending cycles, no cracks occurred in the gold patterns (testing in air). Longer term immersion in saline and in-vivo testing showed some problems related to loss of adhesion and to galvanic effects of the metallization. These observations were leading to some improvements in the fabrication of the encapsulation. In a second packaging iteration of the CMOS chip, these improvements were realized and a new series of encapsulated devices is fabricated. First results are promising, showing improved metal adhesion. Longer term stability tests are on its way.

The objective of this study was to investigate the suitability of embedding passive components in printed circuit boards for space applications. To achieve this goal, an overview of available technologies for component embedding was provided along with their strongpoints and challenges with respect to space projects. The direct embedding of passive components in printed circuit boards was evaluated in depth to determine its performance and reliability. Characterization and reliability investigation were performed using a dedicated test board containing embedded resistors and capacitors. A Spacecraft Interface Module (SIM) board, part of the Advanced Data and Power Management System developed by QinetiQ Space, was redesigned using embedded passive components to demonstrate the capabilities of the technology. Procurement of components for embedding and other logistic aspects were evaluated in this exercise. The outcome of this study aids ESA in determining which projects can benefit from this technology and what procedures for procurement and validation need to be followed.

In this study, the impregnated fibre bundle test, a common method used by carbon and glass fibre manufacturers to determine the properties of fibres used in composites, was adapted for natural fibres and validated by a round robin test on one type of natural fibres, namely flax fibres. Five European laboratories have carried out in parallel the impregnated fibre bundle test, on the same batch of hackled flax (long fibres), to check the applicability and reliability of this modified method on natural fibres. The results were compared to the more traditional single fibre test on elementary fibres. The back-calculated fibre stiffness shows a very low scatter between the five laboratories of less than ±5% (59.8 ± 2.4 GPa, as measured between 0 and 0.1% strain). The fibre ultimate tensile strength of 527 ± 138 MPa has a higher scatter, compared to stiffness values, as this property is highly sensitive to imperfections and flaws.

This paper deals with an alternative testing approach for quantifying the life time of board level solder joint reliability of components. This approach consists of applying a relative shear displacement between component and Printed Circuit Board (PCB) through cyclic board bending. During the cycling, the temperature is kept constant, preferably at elevated temperature in order to fasten the creep deformation of the solder joint. This is done in a four-point bending setup which allows to apply an equal loading on all components lying between the inner bars. The scope of the paper is, firstly, to evaluate if the four point bending testing generates the same fatigue fracture as in thermal cycling; secondly, that the measured life times can be also predicted through finite element simulations; and thirdly if the technique can finally fasten the cycling frequency to gain testing time.

To realize optimal recording and stimulation of peripheral nerve cells, a CMOS chip is made with a multitude of electrodes which can be individually addressed in order to select after implantation the 16 best positioned electrodes. Since the Foreign Body Reaction should be minimal for optimum electrode-nerve contact, the CMOS chip is thinned down to 35um and fully packaged resulting in a 75um thin encapsulated chip. The chip is embedded in a biocompatible stack consisting of polymers and inorganic diffusion barriers deposited using atomic layer deposition (ALD). A biocompatible metallization is realized using gold and platinum sandwiched between polymers and ALD layers for flexible interconnects, and iridium oxide (IrOx) is selected as electrode material for optimal charge injection during stimulation. After this dedicated packaging based on the FITEP technology platform (Flexible Implantable Thin Electronic Package), the CMOS chip is still fully functional, which was tested dry (in air) as well as during submersion in saline. The form factor of the packaged chip is optimized for intra-fascicular implantation with minimum tissue damage. First acute in vivo stimulation tests proved that the stimulation capabilities of the IrOx electrodes are very good.

The investigation of the impact performance of flax-based composites is the key in order to understand which material parameters determine the safety and longevity of flax composite products. In this study, the effect of fibre architectures and matrix type on the absorbed energy after perforation, on the damage resistance as well as on the residual properties after impact were investigated. The matrix choice (epoxy vs MAPP) was found to greatly influence the absorbed energy as well as the damage area. The absorbed energy at perforation for the flax-MAPP composite was more than 50% higher compared to the flax-epoxy composites. Overall, the type of architecture has been found to have a limited effect on the absorbed energy at perforation. Furthermore, the use of a ductile thermoplastic matrix results in a decreased impact damage area by 38–59% with little delamination growth. The flax-epoxy composites experienced a stronger decrease in properties after impact, however these quasi-static properties are still much higher than the flax-MAPP composites.

We present a str etchable and foldable passive matrix driven display using 45 by 80 RGB LED's mounted on a meandering printed circuitry embedded in a polyurethane film. The meander interconnections have been optimized with respect to their electrical and mechanical properties to provide a display with a 3 mm pitch between the pixels and a stretchability of up to 10%. At an operating supply voltage of 5 V, the brightness of the display exceeds 30 cd/m2.

Penetration impact resistance is one of the key advantages of self-reinforced composites. This is typically measured using the same setup as for brittle fibre composites. However, issues with the test configuration for falling weight impact tests are reported. Similar issues have been found in literature for other composites incorporating ductile fibres. If the dimensions of the test samples are too small relative to the clamping device, then the test samples can heavily deform by wrinkling and necking. These unwanted mechanisms should be avoided as they absorb additional energy compared to properly tested samples. Furthermore, these mechanisms are found to occur more easily at lower compaction temperatures due to the lower interlayer bonding. In conclusions, the sample dimensions of ductile fibre composites should be carefully selected for penetration impact testing. If wrinkling or necking is observed, then the sample dimensions need to be increased.

The specific stiffness of flax fibres is comparable to that of glass fibres. However, the application of flax fibres in composites still poses two important problems. The orientation of the fibres in the composite is not impeccable and the fibre–matrix adhesion is too weak. This research focuses on the former. To produce a continuous yarn for the textile industry, technical flax fibres are spun. The twisting of the fibres increases the yarn strength but the orientation of the fibres with regard to the fibre axis decreases. Experiments show that the slightly twisted yarns and the spun yarns possess the best processability but have lower mechanical properties than untwisted ribbons. The values fit very well to certain models which predict stiffness with regard to the twist angle.

Novel insights regarding the ability of encapsulated metal interconnections to deform due to bending are presented. Encapsulated metal interconnections are used as electric conductor or measurement system within a wide range of applications fields, e.g. biomedical, wearable, textile applications. Nevertheless the mechanical analysis remains limited to reliability investigation of these configurations while deformability is as important for application fields where, so-called disappearing electronics is the main purpose. An analysis based on the work needed to bend interconnections to a certain curvature will be used to compare different interconnection configurations with each other. The experimental as well as the simulation setup is based on PDMS encapsulated PI-enhanced Cu tracks. The results and conclusions are specific for this type of interconnections, but can be extended to a global conclusion about stretchable interconnections. From the obtained insights it is proven that periodically meander-shaped interconnections need significant less work, up to more than 10 times less, to bend the interconnection to the same curvature compared to straight interconnection lines. Furthermore, the bendability of the straight interconnection lines is determined by the shape of the interconnection, where for meandered tracks the encapsulation will determine this factor, for an encapsulation thickness of maximum 1 mm. It shows out, for the meander-shaped interconnection, that per increase of 250μm encapsulation thickness the work raises with a factor 2. For straight interconnection lines the work in function of the encapsulation thickness is limited to 20%/250μm. For encapsulations > 1mm, the encapsulation thickness will become the predominant factor which determines the deformability for both interconnection shapes.

Measuring the quality of human health and well-being is one of the key growth areas in our society. Preferably, these measurements are done as unobtrusive as possible. These sensoric devices are then to be integrated directly on the human body as a patch or integrated into garments. This requires the devices to be very thin, flexible and sometimes even stretchable. An overview will be given of recent technology developments in this domain and concrete application examples will be shown.

Self-reinforced polypropylene is a very tough material. It is even thought that its impact resistance increases with decreasing temperature. This was investigated by examining the constituent tapes and matrix. Tensile tests on both drawn polypropylene tapes and self-reinforced polypropylene were similar: the stiffness increased and the failure strain slightly decreased at low temperatures. The matrix, however, embrittled below room temperature due to the glass transition. In contrast with literature data on Izod impact resistance, the penetration impact resistance did not increase at low temperatures. At lower temperatures, the damaged area after non-penetration impact was significantly reduced. This was caused by a change in the damage mode from tape–matrix debonding to matrix cracking, as the matrix went through its glass transition. These conclusions provide the first understanding of the failure behaviour of self-reinforced polypropylene below room temperature, and can be exploited to further optimise the excellent impact resistance of self-reinforced polymers.

Hot compacted self-reinforced polypropylene composites have good tensile properties and excellent impact resistance, but they have a limited processing window. Therefore, the influence of compaction temperature, dwell time and the application of interleaved films on the tensile and impact properties was assessed. Increased compaction temperature allows more molecular relaxation, thereby melting more matrix and creating a stronger interlayer bonding. This results in reduced 0° tensile properties and penetration impact resistance, while the 45° tensile properties and non-penetration impact resistance are maintained or improved. The dwell time only has minor influences on tensile and impact properties, while interleaved films have a similar influence as increased compaction temperature. These films increase the interlayer bonding, which increases the tensile strength and non-penetration impact resistance, but reduces penetration impact resistance. This paper demonstrates a wide property range depending on the processing parameters, helping in future tailoring of self-reinforced composites to specific applications.

In this paper, a detailed power integrity study is described that compares the behavior of surface-mount devices and embedded components for power decoupling. Through measurements and simulations, it is found that when the layer count of the board is low, there is no significant difference between both technologies. When the number of layers increases, the short connection for the embedded components is clearly superior to the surface-mount capacitor. The resonance frequencies for the embedded capacitor do not change significantly with the increased layer count. The case with the surface-mount capacitor however, shows a large increase in parasitic inductance due to the long vias through the board.

Conformable electronics, i.e., electronics that can be applied on curved surfaces, is demanded nowadays in place of conventional rigid printed circuit board (PCB) based electronics for a number of applications. In the field of stretchable electronics there has been a swift progress in recent years. In this paper we are presenting our contribution to this ever growing topic, including thin-film based polyimide (PI), supported Au stretchable meanders as well as PCB based Cu meanders. These meanders are supported by PI or poly(ethylene naphthalate)/poly(ethylene terephthalate) (PEN/PET) films. Thin-film based stretchable interconnects is targeting mainly the biocompatible environments with demands for strong miniaturization while the PCB based technology is used more for large area applications. Both approaches are reviewed in this paper in terms of fabrication processes, materials and cyclic fatigue reliability. For each technology fabricated demonstrators are presented as well.

The technology development for a low-cost, roll-to-roll compatible chip embedding process is described in this paper. Target applications are intelligent labels and disposable sensor patches. Two generations of the technology are depicted. In the first version of the embedding technology, the chips are embedded in an adhesive layer between a copper foil and a PET film. While this results in a very thin (< 200 μm) and flexible system, the single-layer routing and the incompatibility with passive components restricts the application of this first generation. The double-sided circuitry embedding technology is an extension of the single-sided, foil-based chip embedding, where the PET film is replaced by a second metal foil. To obtain sufficient mechanical strength and to further reduce cost, the adhesive film is replaced by a substrate material which is compatible with the chip embedding concept. Both versions of the foil-based embedding technology are very versatile, as they are compatible with a broad range of polymer materials, for which the specifications can be tuned to the final application.

This paper describes the influence of polydopamine surface modifications on the adhesion strength of electroless deposited copper on roughened epoxy resin substrates. The surfaces are characterized with XPS and ToF-S-SIMS. Next, a thorough investigation of the copper-epoxy interface is performed using SEM. Both the polydopamine modification and the variation of the electroless plating bath temperature lead to new insights into the different contributions of chemical and physical adhesion to the overall adhesion strength. (C) Koninklijke Brill NV, Leiden, 2012