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1 – 10 of over 1000Jan Vanfleteren, Thomas Loeher, Mario Gonzalez, Frederick Bossuyt, Thomas Vervust, Ingrid De Wolf and Michal Jablonski
In the past 15 years stretchable electronic circuits have emerged as a new technology in the domain of assembly, interconnections and sensor circuits and assembly technologies. In…
Abstract
Purpose
In the past 15 years stretchable electronic circuits have emerged as a new technology in the domain of assembly, interconnections and sensor circuits and assembly technologies. In the meantime a wide variety of processes with the use of many different materials have been explored in this new field. The purpose of the current contribution is for the authors to present an approach for stretchable circuits which is inspired by conventional rigid and flexible printed circuit board (PCB) technology. Two variants of this technology are presented: stretchable circuit board (SCB) and stretchable mould interconnect (SMI).
Design/methodology/approach
Similarly as in PCB 17 or 35 μm thick sheets of electrodeposited or rolled‐annealed Cu are structured to form the conductive tracks, and off‐the‐shelf, standard packaged, rigid components are assembled on the Cu contact pads using lead‐free solder materials and reflow processes. Stretchability is obtained by shaping the Cu tracks not as straight lines, like in normal PCB design, but as horseshoe shaped meanders. Instead of rigid or flexible board materials, elastic materials, predominantly PDMS (polydimethylsiloxane), are used to embed the conductors and the components, thus serving as circuit carrier. The authors include some mechanical modeling and design considerations, aimed at the optimization of the build‐up and combination of elastic, flexible and rigid materials towards minimal stress and maximum mechanical reliability in the structures. Furthermore, details on the two production processes are given, reliability findings are summarised, and a number of functional demonstrators, realized with the technologies, are described.
Findings
Key conclusions of the work are that: supporting the metal meanders with a flexible carrier prior to embedding in an elastic substrate substantially increases the reliability under mechanical stress (cyclic uniaxial stretching) of the stretchable interconnect and the transition areas between rigid components and stretchable interconnects are the zones which are most sensitive to failure under mechanical stress. Careful design and technology implementation is necessary, providing a gradual transition from rigid to flexible to stretchable parts of the circuit.
Originality/value
Technologies for stretchable circuits, with the same level of similarity to standard PCB manufacturing and assembly, and thus with the same high potential for transfer to an industrial environment and for mass production, have not been shown before.
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To present a method to model woven fibre reinforced metal matrix composite for multilayer circuit boards.
Abstract
Purpose
To present a method to model woven fibre reinforced metal matrix composite for multilayer circuit boards.
Design/methodology/approach
This paper presents a hybrid modelling method to model multilayer multimaterial composites with the combination of metallic and woven composite plies. Firstly, 3D unit cells of woven composite are idealized as orthotropic plies, while metallic layers are taken as isotropic plies. Secondly, the idealized composite plies and metallic plies are modelled into a 2D multilayer finite element (FE). Lastly, scalar damage parameters are used for damage modelling.
Findings
Based on this method, static and dynamic analysis of multilayer composite can be performed at both micro and board levels. Meanwhile, the hybrid model illustrates a good agreement with the experimental results and good computational efficiency required for FE simulation. Conceptually, this study is aimed to provide an efficient damage modelling techniques for laminate composites and flexible modelling methodology for further development of new composite material systems.
Research limitations/implications
Damaging testing and simulation is not involved, although damaging modelling method is presented.
Originality/value
This model has high flexibility and efficiency: the micro structure and properties of reinforced fibres, polymer matrix and metallic plies can be changed conveniently in 3D mechanics unit‐cell model; the 2D structure of geometry model provides a high‐computational efficiency in the numerical simulation. The presented work also provides the damage modelling methods, multi‐linear damage law and scalar damage parameters, to simulate damage behaviour after impact.
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Mario Gonzalez, Fabrice Axisa, Frederick Bossuyt, Yung‐Yu Hsu, Bart Vandevelde and Jan Vanfleteren
The purpose of this paper is to present an update on the progress of the design and reliability of stretchable interconnections for electronic circuits.
Abstract
Purpose
The purpose of this paper is to present an update on the progress of the design and reliability of stretchable interconnections for electronic circuits.
Design/methodology/approach
Finite element modelling (FEM) is used to analyse the physical behaviour of stretchable interconnects under different loading conditions. The fatigue life of a copper interconnect embedded into a silicone matrix has been evaluated using the Coffin‐Manson relation and FEM.
Findings
The mechanical properties of the substrate and the design of the metal interconnection play an important role on the fatigue lifetime of circuit. In the case of copper embedded into a PDMS Sylgard 186, more than 2,500 tensile cycles have been observed for a periodic deformation of 10 per cent.
Research limitations/implications
Reliability results are limited and need further work to create a more accurate empirical model to estimate the lifetime of stretchable interconnections.
Originality/value
The combined use of FEM and experimental analysis enable a more reliable design of the stretchable metal interconnections. The proposed horseshoe design offers the benefit of reduced permanent damage during elongation.
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In Part 1, background information on mechanical properties and metallurgy of solder alloys and soldered joints has been presented. In Part 2, mechanisms of damage and degradation…
Abstract
In Part 1, background information on mechanical properties and metallurgy of solder alloys and soldered joints has been presented. In Part 2, mechanisms of damage and degradation of components and soldered joints during soldering, transport and field life have been discussed, the most important mechanism being low cycle fatigue of the solder metal. In this third part, the determination of the fatigue life expectancy of soldered joints is discussed. Accelerated testing of fatigue is needed, as the possibilities of calculations are strongly limited. A temperature cycle test under specified conditions is proposed as a standard. A model is worked out for the determination of the acceleration factor of this test. A compilation of a number of solder fatigue test results, generated in the author's company, is presented.
This paper presents a magnetoelastic dynamic FE model. As first approach, the effect of magnetostriction and strong coupling is not considered. The effect of Rayleigh damping…
Abstract
This paper presents a magnetoelastic dynamic FE model. As first approach, the effect of magnetostriction and strong coupling is not considered. The effect of Rayleigh damping factors on the vibrational behaviour of the stator core of a synchronous generator is studied using the presented model. It shows that the static approach is not accurate enough and the difference between calculations with damped and undamped cases is too important to be ignored. However, the difference between damped cases with reasonable damping is not very important.
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J. Lau, S. Golwalkar, P. Boysan, R. Surratt, R. Forhringer and S. Erasmus
The reliability of 0.5 mm pitch, 32‐pin thin small outline package (TSOP) solder joints has been studied by experimental temperature cycling and a cost‐effective 3‐D non‐linear…
Abstract
The reliability of 0.5 mm pitch, 32‐pin thin small outline package (TSOP) solder joints has been studied by experimental temperature cycling and a cost‐effective 3‐D non‐linear finite element analysis. Temperature cycling results have been presented as a Weibull distribution, and an acceleration factor has been established for predicting the failure rate at operating conditions. Thermal fatigue life of the corner solder joints has been estimated based on the calculated plastic strain, Coffin‐Manson law and isothermal fatigue data on solders. A correlation between the experimental and analytical results has also been made. Furthermore, failure analysis of the solder joints has been performed using scanning electron microscopy (SEM) and an optical method. Finally, a quantitative comparison between the Type‐I and Type‐II TSOP solder joints has been presented.
Grzegorz Wroblewski, Marcin Słoma, Daniel Janczak and Malgorzata Jakubowska
The aims of this paper are to investigate the influence of direct current (DC) electric field on separation and orientation of carbon nanotubes (CNTs) in spray-coated layers and…
Abstract
Purpose
The aims of this paper are to investigate the influence of direct current (DC) electric field on separation and orientation of carbon nanotubes (CNTs) in spray-coated layers and apply this method to the fabrication of elastic and transparent electrodes. The orientation of CNTs in the form of paths in the direction of electrical conduction should increase the electrode conductivity without decreasing its optical transmission.
Design/methodology/approach
Materials are deposited using vacuum-free, ultra-fine nozzle spray coating technique, easily applicable for large-scale production. After the deposition of carbon nanomaterials, nanoparticles are oriented in the electric field and initially cured with infrared halogen lamp to evaporate solvents and preserve orientation of the nanoparticles in the deposited layer. Afterwards, layers are cured in a chamber dryer to obtain desired properties. Nanoparticles orientation and carbon nanomaterials separation via DC electric field are analysed, and the optical and electrical properties of prepared electrodes are measured.
Findings
Experiments described in this paper showed that DC electric field can be applied provide separation and orientation of CNTs and combined with spray coating technique, can be used as additional tool for tuning the conductivity of flexible and transparent electrodes by decreasing the sheet resistance about five times.
Originality/value
The results showed that spray coating combined with electric field orientation is a promising solution of obtaining elastic and transparent electrodes with oriented carbon particles. According to the authors’ knowledge, none of the experiments was directed to obtain DC electric field-oriented transparent layers produced with the use of spray coating technique.
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Silicones have long been recognised as attractive materials for use in electronics applications because of their unique combination of properties. Now, technology which couples…
Abstract
Silicones have long been recognised as attractive materials for use in electronics applications because of their unique combination of properties. Now, technology which couples high electrical conductivity with silicone performance characteristics has been developed. The new silver‐filled silicone adhesives were processed and cured in a manner similar to that used in conventional heat cured silicone compositions. Resultant cured products were both highly flexible and highly conductive, exhibiting volume resistivities down to 2 × 10−4 ohm‐cm. Both flexibility and electrical conductivity were retained after extended periods at elevated temperature. The electrical performance obtained while the new adhesives were under strain (induced either mechanically or thermally) was attributed to changes in the spatial packing of the silver. Low temperature characterisation indicated that the materials remain soft and stress‐relieving even down to −60°C. Other physical characteristics of these compositions, such as high ionic purity, low moisture uptake and good adhesion, are typical of high performance electrically conductive adhesives. This combination of properties suggests that these new silicone adhesives should be attractive for the electrical interconnection of microelectronics substrates having a mismatch of thermal coefficients of expansion (TCE) which would normally lead to failure due to thermomechanical stresses, and for the manufacture of flexible circuitry.