EURO-ECOLE: Assessment of the Bioavailability and Potential Ecological Effects of Copper in European Surface Waters ; subproject 4: Evaluation and improvement of the ecological relevance of laboratory generated toxicity data

This report summarizes the acute and chronic toxicity of copper to algae, Daphnia and a few other freshwater species in standard laboratory test water and a wide range of natural surface waters (collected across Europe), with a wide range of pH, dissolved organic carbon (DOC) concentration and hardness. These data can be used for validation of bioavailability models such as the biotic ligand model (BLM)

Stretchability : the metric for stretchable electrical interconnects

Stretchable circuit technology, as the name implies, allows an electronic circuit to adapt to its surroundings by elongating when an external force is applied. Based on this, early authors proposed a straightforward metric: stretchability—the percentage length increase the circuit can survive while remaining functional. However, when comparing technologies, this metric is often unreliable as it is heavily design dependent. This paper aims to demonstrate this shortcoming and proposes a series of alternate methods to evaluate the performance of a stretchable interconnect. These methods consider circuit volume, material usage, and the reliability of the technology. This analysis is then expanded to the direct current (DC) resistance measurement performed on these stretchable interconnects. A simple dead reckoning approach is demonstrated to estimate the magnitude of these measurement errors on the final measurement

Free-form 2.5D thermoplastic circuits using one-time stretchable interconnections

A technology is presented for the production of soft and rigid circuits with an arbitrary 2.5D fixed shape. The base of this technology is our proprietary technology for elastic circuits with a random shape, in which the elastic thermoset (mostly PDMS) polymer is now replaced by soft or rigid thermoplastic variants. An additional thermoforming step is required to transform the circuit from its initial flat to its final fixed 2.5D shape, but for rigid fixed shape circuits only one-time stretchability of the extensible interconnects is required, relieving the reliability requirements

Thermo-mechanical analysis of flexible and stretchable systems

This paper presents a summary of the modeling and technology developed for flexible and stretchable electronics. The integration of ultra thin dies at package level, with thickness in the range of 20 to 30 μ m, into flexible and/or stretchable materials are demonstrated as well as the design and reliability test of stretchable metal interconnections at board level are analyzed by both experiments and finite element modeling. These technologies can achieve mechanically bendable and stretchable subsystems. The base substrate used for the fabrication of flexible circuits is a uniform polyimide layer, while silicones 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 relatively rigid polyimide by a soft and elastic silicone material. 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

Stretchable mould interconnect optimization : peeling automation and carrierless techniques

The primary bottleneck of the stretchable mold interconnect (SMI) technology is its reliance on carrier boards. These are necessary to handle the meandered circuit during production and to ensure dimensional stability of the flexible circuit board before encapsulation. However, for all the problems it solves, it also introduces a new major problem by requiring a peeling step – which is difficult to automate. This manuscript aims to present some of the work that went into eliminating this problem, discussing both unsuccessful and functioning methods to tackle this conundrum and some of the experimental work that went into verifying these techniques. First, alterations to the design to simplify peeling are considered, followed by adhesivebased peeling processes and mechanical pin-based systems. Next, masking and structuring of the carrier board adhesive are considered. Finally, two carrierless methods which circumvent the problems are discussed, a two-step process – which cuts temporary support structures after partial encapsulation – and a technique whereby the frame is designed to fail in a controlled manner during the first use of the circuit, creating a carrierless process feasible for high-volume production

One-time deformable thermoplastic devices based on flexible circuit board technology

This contribution describes an efficient process flow for production of one-time deformable electronic devices based on standard circuit board technology and demonstrates multiple devices fabricated using this technique. The described technology has the potential to streamline and simplify the production of complex user interfaces which typically require extensive mechanical design and many components. The employed technique allows for the production of complex 3D shapes without the need to modify existing circuit board manufacturing equipment or processes significantly. To achieve this the device is manufactured in a flat state, encapsulated in a thermoplastic polymer laminate and deformed afterwards. This allows the usage of standard electronic components in surface mount packages, which are assembled using lead-free high-temperature solder. The circuit is deformed using a high-volume cost-effective thermoforming approach, where the encapsulating polymer is heated above its glass transition temperature and forced against a mold where it is allowed to cool down again. To enable significant out-of-plane deformations stretchable meandering interconnects are used, which were traditionally developed for dynamically stretchable devices. Fabrication of the circuit starts using a standard flexible copper clad laminate which is processed using the default techniques, the resulting circuit is then attached to a carrier board coated with a reusable high-temperature pressure sensitive adhesive. The interconnect and circuit outline is then defined using laser routing or punching, cutting the flexible circuit without damaging the carrier. The residuals not part of the circuit are removed, in a process akin to protective film removal, and solder paste is stencil printed on the circuit. Afterwards components are placed using a pick-and-place machine and the boards are reflow soldered. After functional testing and repair (if necessary) the circuits are placed in a vacuum press with a thermoplastic laminate, consisting of a thermoplastic elastomer and a rigid thermoplastic sheet. During this lamination the components are protected by a highly conforming press pad. Because the adhesion between the elastomer and the circuit far exceeds that between the circuit and the carrier the circuit is released readily as the thermoplastic laminate is peeled away. The resulting laminate is built up further using thermoplastic films and sheets, and finally deformed using a vacuum forming machine. The resulting device, which is trimmed to remove the clamping edges, can then be mounted in the final assembly. The advantages of this approach are demonstrated using a series of test vehicles, demonstrating the integration of complex circuits, connectors, and power circuitry. Finally, a series of design considerations that became apparent after initial reliability testing are discussed, together with the resulting design rules