A new low cost, elastic and conformable electronics technology for soft and stretchable electronic devices by use of a stretchable substrate

A growing need for ambient electronics in our daily life leads to higher demands from the user in the view of comfort of the electronic devices. Those devices should become invisible to the user, especially when they are embedded in clothes (e.g. in smart textiles). They should be soft, conformable and to a certain degree stretchable. Electronics for implantation on the other hand should ideally be soft and conformable in relation to the body tissue, in order to minimize the rejecting nature of the body to unknown implanted rigid objects. Conformable and elastic circuitry is an emerging topic in the electronics and packaging domain. In this contribution a new low cost, elastic and stretchable electronic device technology will be presented, based on the use of a stretchable substrate. The process steps used are standard PCB fabrication processes, resulting in a fast technology transfer to the industry. This new developed technology is based on the combination of rigid standard SMD components which are connected with 2-D spring-shaped metallic interconnections. Embedding is done by moulding the electronic device in a stretchable polymer. The reliability of the overall system is improved by varying the thickness of the embedding polymer, wherever the presence and type of components requires to. Manufacturability issues are discussed together with the need for good reliability of the stretchable interconnections when stress is applied during stretching

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 engineering technologies for the development of advanced stretchable polymeric systems

For advanced body related applications, there is a need of soft, conformable, elastic, mechanical compliant and washable systems. Smart clothes for health monitoring, sport or professional protection need washable and conformable electronic systems, which can be deformed up to 20%. Implants, like monitoring sensors, or functional implants, need softness, stretchability to comply with the human body, chemical resistance, and biocompatibility. Many technologies are already available, like polyimide or PET/PEN based flexible electronic system, or conductive yarns for textile which can be knitted or embroidered to produce textrodes or textile based electronic systems. However softness and interconnections are still problems. Polymers based electronic system or stretchable electronic systems are a possible solution. We have developed several technologies to produce stretchable electronics systems. They are based on the concept of flexible functional islands, onto which standard SMD components are soldered, interconnected with meanders shaped metallic stretchable interconnections. Metallic interconnections are made from copper or gold and are optimized using FEM analysis. Stretchable electronic systems are then molded in elastomeric (e.g. silicone rubber or polyurethane) matrix. They can sustain at least 100% of elongation and 3000 cycles at 20% of elongation. They can be integrated in textile and they are biocompatible and washable

Water permeability and carbonation on foamed concrete

Foamed concrete is a controlled density low strength material with density ranging from 300 kg/m3 to 1800 kg/m3 suitable for construction of walls. The acceptance of foamed concrete blocks and panels by the Construction Industry Development Board of Malaysia as components of industrialized building system has promoted its commercial applications. It is made of cement, fine sand, water and preformed foam. Its self-compacting properties have enhanced productivity for mass production. Previous studies revealed findings on the use of large volume partial cement replacement materials without adverse effect on its physical and mechanical properties. This study focused mainly on the effect of the density of foamed concrete on carbonation and water permeability. The ability to vary the density of foamed concrete is considered a unique characteristic compared with normal concrete. Carbonation is usually considered as a negative impact on reinforced concrete. It is the process of pH reduction of concrete from 12.6 to 9.0 in the presence of carbon dioxide and moisture. The reduction of alkalinity means the loss of protection against corrosion to steel bars embedded within concrete. However, for non�structural applications of foamed concrete in wall construction without steel bars or with the use of corrosion inhibitor, carbonation is turned into an advantage for sustainable construction. The ability of foamed concrete to speed up the absorption of carbon dioxide is an important aspect to be explored for its potential use in reducing carbon footprint from the construction industry. The objective of this study is to explore a relationship between carbonation depth, water permeability and the density of foamed concrete. The laboratory tests were conducted on concrete cubes and prisms for up to one and a half years. The water permeability method was developed based on ISO/DIS 7031. The test results indicate that increasing density of foamed concrete tends to reduce its water permeability and carbonation depth. vi The plot of carbonation depth against permeability coefficient produces a linear relationship. The rate of carbonation was found to be inversely proportional to the square root of density. An empirical formula incorporating density as a variable based Currie’s formula is produced. This finding is expected to excite researchers who are concerned with the use of concrete for sustainable construction. Its tendency to absorb carbon dioxide faster than normal concrete from the atmosphere in the carbonation process is expected to lead to widespread use of foamed concrete for environmental and economical advantage

Industrial and technical aspects of chip embedding technology

Embedding of semiconductor chips into organic substrates allows a very high degree of miniaturization by stacking multiple layers of embedded components, superior electrical performance by short and geometrically well controlled interconnects as well as a homogeneous mechanical environment of the chips, resulting in good reliability. At PCB manufacturing level, 50 mum thin chips have been embedded with pitches up to 200 mum in up to 18ldquotimes24rdquo panels. Embedding of chips at 100 mum pitch has been achieved at prototype level. Further developments of chip embedding can extend to even finer pitches without redistribution methods only with concurrent developments in ultra fine line patterning, plating methods and chemistries, assembly machines. New manufacturing processes should combine PCB processing and die assembly in one production line in order to benefit the most from this combination without the difficulties of transport between different manufacturing plants. Furthermore, new testing methodologies will be developed and a new supply chain will be created due to incorporation of embedding technologies to PCB production. This paper discusses in detail the technology and manufacturing challenges arisen from the integration of embedding technologies to PCB manufacturing processes

Printing fine solid lines in flexographic printing process

Solid lines are essential to enable printing of conducting tracks for various electronic applications. In the flexographic printing process, the behaviour of the printing plate plays a vital role in how ink is printed onto the substrate as it deforms when passing through the printing nip. This deformation is dependent on the material properties of the plate, the geometry of the lines and the pressure within the printing nip. These will influence the printed track width and the ink film thickness, which will affect the electrical performance of the printed conductors. This thesis will focus on experiments on Flexographic printing capabilities in printing ultra fine solid lines. The development of a measurement technique which leads to successfully capturing the printing plate line geometry details through the application of interferometry techniques, will be demonstrated. This information is used in a Finite Element models to predict the deformation and consequent increase in line width using both a linear and non linear material models, the latter being based on a hyperelastic representation. A series of experiments on a bench top printer and a web press machine to determine the capabilities and the limitation of the Flexographic printing process in printing fine solid is also presented. Through the experiments conducted the link between the IGT-Fl printer and an industrial scale web press machine has been established where the success in study on certain printing parameters and its affects lead to a successful prints of 50ym line width with 50pm line gaps. The experiments also point the importance of light engagement pressures within the printing train and the requirements for using anilox cylinders having fine engraving. The work also shows than process parameters (eg, contact pressures) that are important for graphics printing have a similar effect when the processes is used to print fine line features .

Illustrations of pro forma financial statements that reflect subsquent events; Financial report survey, 44

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Application of adhesives in MEMS and MOEMS assembly: a review

This paper presents a review of the recent literature on the use of adhesives in MEMS packaging applications. The aim of this review has been to establish the current applications of adhesives in MEMS and MOEMS assembly and to investigate the limitations and future requirements of these materials. The review has shown that while there is a wealth of information available on the packaging of MEMS devices, there is very limited detail available within the public domain regarding the specific uses of adhesives and in particular exactly which products are in use. The paper begins with an overview of the uses of adhesives in MEMS packaging, subdivided into sections on structural adhesives, adhesives for optical applications and other applications. The paper then describes methods for adhesive dispensing and issues with adhesive use which affect the reliability of the package. The reliability of MEMS devices assembled using adhesives is a challenging issue, being more than a simple combination of electrical, mechanical and material reliability. Many failure modes in MEMS devices can be attributed to the adhesives used in the assembly; for example, thermal expansion mismatches can cause stress in the die attach, while outgassing from epoxies can cause failure of sealed devices and contamination of optical surfaces

Doctor of Philosophy

dissertationThree-dimensional (3D) rapid prototyping holds significant promise for future antenna designs. Many complex designs that would be unmanufacturable or costly are realizable on a 3D printing machine. The ability to create 3D designs of virtually any configuration makes it possible to build compact antennas that can form fit to any space. These antennas build on the concept that small antennas can best reach the ideal operating limit when utilizing the entire 3D space in a sphere surrounding the antenna. Antennas require a combination of dielectric and conductive materials. 3D rapid prototyping is already well advanced for plastics and dielectric materials (with more options coming online). Prototyping with conductive materials has lagged behind; due mainly to their higher melting points, but this is advancing as well. This dissertation focuses on 3D rapid prototyping for antenna design. A 3D antenna made from small cubical cells is optimized for 2.4-3GHz using a genetic algorithm (GA). The antennas are built using 3D printing of plastic covered by conductive paint. The effects of the conductivity of the paint and number of layers on the resonance and gain of the antenna are evaluated. These results demonstrate the feasibility of using 3D rapid prototyping for antenna design