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Abstract: Tactile shear sensors gain importance for example in the field of robotics and biomedical sciences. For these applications, an “artificial skin”-like solution is needed with very thin and flexible unobtrusive sensors that can be wrapped around irregular surfaces or body parts. We present a tactile shear sensor based on the changing optical coupling between a light source (Vertical-Cavity Surface-Emitting Laser (VCSEL)) and a photodiode, separated by a transparent deformable transducer layer. When shear stress is applied onto the stack, both components move laterally and the photodiode captures a differing amount of light. Commercially available bare die VCSELs and photodiodes were thinned down to 20colonm and then packaged in flexible polyimide foils (40colonm thick) to allow fabricating this flexible and thin sensor. The use of spin-coatable polyimide resulted in low-stress packages for these optoelectronics. [Copyright &y& Elsevier]

For future construction of implantable tissue structures, the development of 3-dimensional fluidic microsystems is necessary. In the current work we have developed a unique technology for 3-dimensional microfluidic environments with potential for tissue engineering applications. The microfluidic devices were fabricated out of biodegradable and biocompatible elastomers, such as poly (glycerol-sebacate) and poly (erythritol-sebacate), due to their transparency and thermoset properties suitable for microfabrication technologies. The three-dimensionality of the microfluidic bioreactors was imparted by a porous poly L-lactic acid membrane prepared via electrospinning. Thus obtained membrane has a high surface area-to-volume ratio and is intended to mimic the extracellular matrix that provides physical support and spatial organization. The membrane was cut and placed in between two micro-patterned microfluidic layers during the alignment process, and subsequently bonded to achieve the final bioreactor. The patency of the device network was evaluated and the bond between the microfluidic layers was sufficiently strong to allow perfusion flow rates in the range 0.1-300 μl/min. The herein developed technology comes as solution to the two-dimensionality issue that exists in most microfluidic devices and can relate to a variety of tissue engineering applications. [ABSTRACT FROM AUTHOR]

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 of recent technology developments in this domain and concrete application examples will be discussed. [ABSTRACT FROM AUTHOR]

In this paper the influence of the epoxy roughness, surface modifications and ELD (electroless copper deposition) temperatures on the adhesive strength of the copper is studied. Good adhesion at low roughness values is targeted due to their applicability in high density electronic circuits. Roughened epoxy surfaces are modified with adsorbed polyamines, polydopamine and polyamines grafted to polydopamine. Next the, adhesive strength of ELD copper is determined with peel strength measurements and the interphases are examined with SEM (scanning electron microscopy). Polydopamine and polyamines grafted to polydopamine can lead to increased adhesive strength at lower roughness values compared to the non-modified samples at specific plating temperatures. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a summary of the modeling and technology developments for flexible and stretchable electronics. These technologies can achieve mechanically bendable and stretchable subsystems by incorporating the electronic circuit into a matrix made of a soft polymer. The base substrate used for the fabrication of flexible circuits is a uniform polyimide layer, while silicones or polyurethanes materials are preferred for the stretchable circuits. The method developed for chip embedding and interconnections is named Ultra Thin Chip Package (UTCP). Extensions of this technology can be achieved by stacking and embedding thin dies in polyimide, providing large benefits in electrical performance and still allowing some mechanical flexibility. These flexible circuits can be converted into stretchable circuits by replacing the polyimide by a soft and elastic silicone material. The integration of ultra thin dies at package level, with thickness in the range of 10–30μm, into flexible and/or stretchable materials are demonstrated. Furthermore, the design and reliability test of stretchable metal interconnections at board level are analyzed by both experiments and finite element modeling. We have shown through finite element modeling and experimental validation that an appropriate thermo-mechanical design is necessary to achieve mechanically reliable circuits and thermally optimized packages. [Copyright &y& Elsevier]

Abstract: The trend of microelectronic products in the textile or medical field is toward higher functionality, miniaturization, application of new materials and a necessity for deformable electronic circuits for improving the comfort control. In this work, the design of flexible and stretchable interconnections is presented. These interconnections are done by embedding sinuous electroplated metallic wires in a stretchable substrate material. A silicone material was chosen as substrate because of its low stiffness and high elongation before break. Common metal conductors used in the electronic industry have very limited elastic ranges; therefore a metallization design is crucial to allow stretchability of the conductors going up to 100%. Different configurations were simulated and compared among them and based on these results, a horseshoe like shape was suggested. This design allows a large deformation with the minimum stress concentration. Moreover, the damage in the metal is significantly reduced by applying narrow metallization schemes. In this way, each conductor track has been split in four parallel lines of 15μm and 15μm space in order to improve the mechanical performance without limiting the electrical characteristics. [Copyright &y& Elsevier]

This paper presents the results from the evaluation of different types of flexible substrates for high-density flip chip application. In this work four different flexible substrates were used. The flex substrates were Espanex, Upilex and epoxy glass with 80 μm pitch and Upilex with 54 μm pitch. Two different test IC’s were used for both pitches. In test IC1 (80 μm pitch) and IC3 (54 μm pitch) the bumps were in one row and test IC2 (80 μm pitch) and IC4 (54 μm pitch) in two rows. The total amount of contacts in test IC1 was 190, in test IC2 173, in test IC3 293 and in test IC4 270. The anisotropically conductive adhesive that was used in the tests was epoxy based thermosetting adhesive film with conductive particles. The conductive particles in the adhesives were isolated soft metal-coated polymer particles. The contact resistance was measured using Kelvin four-point method and the continuity and series resistance using daisy chain structure. The reliability of the flip chip interconnections was tested in temperature cycling test and environmental test. Cross section samples were made to analyse the possible reason for failures. The results presented in this paper are from FLEXIL development project that is part of European Union IST research program. [Copyright &y& Elsevier]