13,383 research outputs found

    Direct-write techniques for maskless production of microelectronics: a review of current state-of-the-art technologies

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    Recently, there has been growing interest in direct-write methods for the manufacturing of microelectronic products, as the entire electronics industry sector is aiming towards low cost, rapid manufacturing and shorter time-to-market, as well as reduced environmental impacts. This paper will review the main direct-write techniques, most of which have been invented or seen significant development during the last decade. These techniques include droplet-based direct writing, such as inkjet printing, filament-based direct writing, such as the Micropen and nScrypt processes, tip based directwrite methods, and laser beam direct writing. For each category, only a few examples are presented, although there are a number of specific methods and variants within each of these categories

    Materials jetting for advanced optoelectronic interconnect: technologies and application

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    This report covers the work carried out on Teaching Company Scheme No. 2275 "Materials Jetting for Advanced Interconnect" between February 1998 and February 2000. The project was conducted at the Harlow laboratories of Nortel Networks with the support of the Department of Manufacturing Engineering of Loughborough University. Technical direction and supervision has been provided by Mr Paul Conway, Reader, at Loughborough University, Professor Ken Snowdon and Mr Chris Tanner of Nortel Networks. The aim of the project was to produce and deposit minute and precise volumes of a range of materials, such as metallic alloys, glasses and polymers, onto a variety of substrates commonly used in the electronics and optoelectronics fields. The technology, which is analogous to ink-jet printing, firstly had to be refined to accommodate higher processing temperatures of up to 350°C. The ultimate project deliverable was to produce a specification for jetting equipment suited towards volume manufacturing. [Continues.

    Development and applications of inkjet printed conducting polymer micro-rings

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    A drying sessile drop moves the solute particles to the periphery where they get deposited in the form of a ring. This phenomenon is prevalent even with micro drops falling at high velocity from a piezo-actuator based inkjet printer. In polymer microelectronic field, this phenomenon is a major challenge for fabricating devices using inkjet printing. We exploited this problem and applied it for various novel applications in the field of polymer microelectronics. Various dispensing techniques and temperature variations for micro-drop printing were used for modifying the micro-drops in such a way that the periphery of the micro-ring holds most of the solute as compared to inner base layer. Reactive ion etching (RIE) was used for removing the inner base layer in order to make the micro-rings completely hollow from the center. These micro-rings were applied in the fabrication of polymer light emitting diode, humidity sensor and vertical channel field effect transistor. High resolution polymer light emitting diode array (\u3e200 pixels/inch) was fabricated by inkjet printing of micro-ring and each micro-ring acts as a single pixel. These micro-rings were applied as a platform for layer-by-layer (LbL) nano-assembly of poly-3,4-ethylenedioxythiophene:poly-styrenesulfonate (PEDOT:PSS) for the fabrication of humidity sensor. Enhanced sensitivity of the humidity sensor was obtained when the inkjet printed micro-rings are combined with LbL assembled PEDOT:PSS films. During the fabrication of vertical channel field effect transistors, inkjet printed PEDOT:PSS micro-rings were used as source and the inner spacers between the adjacent micro-rings were used to make channel. These micro-rings can also find other applications in the field of biological sciences. These micro-rings can be used as cell culture plates and as scaffolds for cell and/or tissue growth

    Aerosol jet deposition of samarium-doped ceria films

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    Direct write processes include a range of additive manufacturing technologies. These technologies are employed to fabricate structures by depositing layer upon layer of functional material. The feature resolutions obtained are often in the micron or sub-micron range. This thesis focuses on use of the Aerosol Jet direct write printing process, which shows promise for the fabrication of ceramic films due to its fine feature resolution and flexibility with printing complex features. This study identifies significant process parameters and their relationship to the process output for deposition of Samarium-doped Ceria (SDC) nano-ink. A design of experiments approach is used to generate a model where height and width of the printed tracks are the response variables of interest. Initial feasible operating ranges for each process parameter were identified. Then fractional factorial screening experiments were designed to identify the significant factors affecting the response variables in the study. Two distinct regression equations were generated to predict width and height. Validation experiments were run to confirm the actual values as compared with the predicted ones. For height, the experiment results suggested lack of curvature as well as the standard error and R-squared values were found satisfactory. For width, a higher order model was designed referring to the results of the validation experiment. For the higher order model a three factor three level experiment was considered. The higher order model gives a much lesser standard error and better fit of residuals as compared to the screening model for width. In addition, the study includes a brief discussion on use of Aerosol Jet printing system to manufacture high aspect ratio structures in addition to its application in thin film deposition. The work further demonstrates printing of a high aspect ratio micro-pillar array as a proof of this concept

    Development of multiwave-based bioprinting technology

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    Pluripotent stem cells (PSCs) are the most favourable sources of cells for tissue engineering applications due to their unique potency and self-renewal characteristics however they are quite fragile and can be directed to differentiate erroneously by the application of external forces. A novel multi-nozzle valve-based bioprinting platform was developed that was able to position droplets of bio-ink – such as cells in suspension – with high spatial accuracy and low impact. Volumes as low as 2 nL were successfully dispensed. Several different versions of the machine were created before the final machine was made integrating improvements and solutions to problems encountered during development. A complete evaluation of cell compatibility was carried out in order to quantify the response of cells to the bioprinting process. In the first ever study of this kind, the viability and pluripotency of human embryonic and induced pluripotent stem cells was investigated post-printing and were found to be almost completely unaffected by the bioprinting process. Many cells require a 3D culture environment in order to maintain their in vivo functions. A hybrid bioprinted-hanging-droplet technique was used to create uniform spheroid aggregates of programmable sizes from PSCs which could be used to direct PSC differentiation or as building blocks for tissue generation. Hydrogels can also be used to recreate the 3D in vivo cellular environment using the bioprinter. Alginate and hybrid polypeptide-DNA hydrogels were used, the latter for the first time with a bioprinting platform. Complex 3D structures could be created in a layer-by-layer approach with programmable heterogeneous properties throughout. Cells were added to the hydrogel precursor solution and used to bioprint 3D structures. The cells were found to be functional and highly viable while being encapsulated throughout the 3D structure of the bioprinted hydrogel which will allow the future creation of more accurate human tissue models. PSCs were successfully directed to differentiate into hepatocyte-like cells. It was shown that the bioprinting process did not interrupt or alter the pre-programmed differentiation of the cells which means that these cells can be patterned in 3D using the bioprinter while differentiating, greatly speeding up the creation of mini-liver tissue. Hepatic stellates and HUVECs were co-cultured with the hepatocyte-like cells in various ratios in an attempt to improve their hepatic function. However, no clear improvement in cytochrome P450 activity was observed indicating that further optimisation is required in this area

    Development of multivalve-based bioprinting technology

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    Pluripotent stem cells (PSCs) are the most favourable sources of cells for tissue engineering applications due to their unique potency and self-renewal characteristics however they are quite fragile and can be directed to differentiate erroneously by the application of external forces. A novel multi-nozzle valve-based bioprinting platform was developed that was able to position droplets of bio-ink – such as cells in suspension – with high spatial accuracy and low impact. Volumes as low as 2 nL were successfully dispensed. Several different versions of the machine were created before the final machine was made integrating improvements and solutions to problems encountered during development. A complete evaluation of cell compatibility was carried out in order to quantify the response of cells to the bioprinting process. In the first ever study of this kind, the viability and pluripotency of human embryonic and induced pluripotent stem cells was investigated post-printing and were found to be almost completely unaffected by the bioprinting process. Many cells require a 3D culture environment in order to maintain their in vivo functions. A hybrid bioprinted-hanging-droplet technique was used to create uniform spheroid aggregates of programmable sizes from PSCs which could be used to direct PSC differentiation or as building blocks for tissue generation. Hydrogels can also be used to recreate the 3D in vivo cellular environment using the bioprinter. Alginate and hybrid polypeptide-DNA hydrogels were used, the latter for the first time with a bioprinting platform. Complex 3D structures could be created in a layer-by-layer approach with programmable heterogeneous properties throughout. Cells were added to the hydrogel precursor solution and used to bioprint 3D structures. The cells were found to be functional and highly viable while being encapsulated throughout the 3D structure of the bioprinted hydrogel which will allow the future creation of more accurate human tissue models. PSCs were successfully directed to differentiate into hepatocyte-like cells. It was shown that the bioprinting process did not interrupt or alter the pre-programmed differentiation of the cells which means that these cells can be patterned in 3D using the bioprinter while differentiating, greatly speeding up the creation of mini-liver tissue. Hepatic stellates and HUVECs were co-cultured with the hepatocyte-like cells in various ratios in an attempt to improve their hepatic function. However, no clear improvement in cytochrome P450 activity was observed indicating that further optimisation is required in this area

    Digitally driven microfabrication of 3D multilayer embedded electronic systems

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    The integration of multiple digitally driven processes is seen as the solution to many of the current limitations arising from standalone Additive Manufacturing (AM) techniques. A technique has been developed to digitally fabricate fully functioning electronics using a unique combination of AM technologies. This has been achieved by interleaving bottom-up Stereolithography (SL) with Direct Writing (DW) of conductor materials alongside mid-process development (optimising the substrate surface quality), dispensing of interconnects, component placement and thermal curing stages. The resulting process enables the low-temperature production of bespoke three-dimensional, fully packaged and assembled multi-layer embedded electronic circuitry. Two different Digital Light Processing (DLP) Stereolithography systems were developed applying different projection orientations to fabricate electronic substrates by selective photopolymerisation. The bottom up projection orientation produced higher quality more planar surfaces and demonstrated both a theoretical and practical feature resolution of 110 μm. A top down projection method was also developed however a uniform exposure of UV light and planar substrate surface of high quality could not be achieved. The most advantageous combination of three post processing techniques to optimise the substrate surface quality for subsequent conductor deposition was determined and defined as a mid-processing procedure. These techniques included ultrasonic agitation in solvent, thermal baking and additional ultraviolet exposure. SEM and surface analysis showed that a sequence including ultrasonic agitation in D-Limonene with additional UV exposure was optimal. DW of a silver conductive epoxy was used to print conductors on the photopolymer surface using a Musashi dispensing system that applies a pneumatic pressure to a loaded syringe mounted on a 3-axis print head and is controlled through CAD generated machine code. The dispensing behaviour of two isotropic conductive adhesives was characterised through three different nozzle sizes for the production of conductor traces as small as 170 μm wide and 40 μm high. Additionally, the high resolution dispensing of a viscous isotropic conductive adhesive (ICA) also led to a novel deposition approach for producing three dimensional, z-axis connections in the form of high freestanding pillars with an aspect ratio of 3.68 (height of 2mm and diameter of 550μm). Three conductive adhesive curing regimes were applied to printed samples to determine the effect of curing temperature and time on the resulting material resistivity. A temperature of 80 °C for 3 hours resulted in the lowest resistivity while displaying no substrate degradation. ii Compatibility with surface mount technology enabled components including resistors, capacitors and chip packages to be placed directly onto the silver adhesive contact pads before low-temperature thermal curing and embedding within additional layers of photopolymer. Packaging of components as small as 0603 surface mount devices (SMDs) was demonstrated via this process. After embedding of the circuitry in a thick layer of photopolymer using the bottom up Stereolithography apparatus, analysis of the adhesive strength at the boundary between the base substrate and embedding layer was conducted showing that loads up to 1500 N could be applied perpendicular to the embedding plane. A high degree of planarization was also found during evaluation of the embedding stage that resulted in an excellent surface finish on which to deposit subsequent layers. This complete procedure could be repeated numerous times to fabricate multilayer electronic devices. This hybrid process was also adapted to conduct flip-chip packaging of bare die with 195 μm wide bond pads. The SL/DW process combination was used to create conductive trenches in the substrate surface that were filled with isotropic conductive adhesive (ICA) to create conductive pathways. Additional experimentation with the dispensing parameters led to consistent 150 μm ICA bumps at a 457 μm pitch. A flip-chip bonding force of 0.08 N resulted in a contact resistance of 2.3 Ω at a standoff height of ~80 μm. Flip-chips with greater standoff heights of 160 μm were also successfully underfilled with liquid photopolymer using the SL embedding technique, while the same process on chips with 80 μm standoff height was unsuccessful. Finally the approaches were combined to fabricate single, double and triple layer circuit demonstrators; pyramid shaped electronic packages with internal multilayer electronics; fully packaged and underfilled flip-chip bare die and; a microfluidic device facilitating UV catalysis. This new paradigm in manufacturing supports rapid iterative product development and mass customisation of electronics for a specific application and, allows the generation of more dimensionally complex products with increased functionality

    Electrochemical metal 3D printing

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    Additive manufacturing (AM) is the process of creating 3D objects from digital models through the layer-by-layer deposition of materials. Electrochemical additive manufacturing (ECAM) is a relatively new technique which can create metallic components-based on depositing layers of metal onto the surface of the conductive substrate through the reduction of metal ions. It is advantageous compared to other metal AM processes due to the absence of high temperature processes enabling a lower-cost and safer fabrication process, however, to date, all of the presented ECAM methods (Localized Electrochemical Deposition (LED) and Meniscus Confined Electrochemical Deposition (MCED) have been designed to achieve micro or nanoscale structures with limited deposition rates, and only focused on single material fabrication. Furthermore, all the printed structures are limited in the complexity of geometries, with the majority being wire-based architectures of porous and rough morphologies, with limited characterisation of the properties of the printed structures. Additionally, there is no available system able to create temperature-reactive multi-metallic functional 4D structures and no research has been presented on the potential application of ECAM in the field of electrochemical energy storage devices. To bridge the gaps, this thesis investigates the development of a low-cost ECAM system capable of producing single and multi-metal structures by using multi-meniscus confined extrusion heads with volumetric deposition rates 3 times higher than what has previously been reported (~ 2×104 μm3.s-1), enabling large-scale fabrication of complex structures in multiple metallic materials. Scanning electron microscopy, X-ray computed tomography and energy dispersive X-ray spectroscopy measurements confirm that multi-metallic structures can be successfully created, with a tightly bound interface. Analysis of the thermo-mechanical properties of the printed strips shows that mechanical deformations can be generated in Cu-Ni strips at temperatures up to 300 °C, which is due to the thermal expansion coefficient mismatch generating internal stresses in the printed structures. Electrical conductivity measurements show that the bimetallic structures have a conductivity between those of nanocrystalline copper and nickel. Vicker’s hardness tests, show that there is a clear correlation between the applied potential and the hardness of the printed product, with higher potentials resulting in a harder deposition. This increased hardness was found to be due to the smaller grain sizes produced during higher potential deposition which restricted dislocation movement through the material. Finally, this thesis presents the first reported combination of electrochemical 3D printing and electrospinning for building a high mass loading and high performance copper-fibre based supercapacitor which enables the potential to create more integrated electrodes and eventually to enhance the performance of supercapacitors. The results highlight the influence of the substrate conditioning and the resulting effects on the wetting characteristics of the meniscus and the subsequent distribution of the deposition which impacts the electronic conductivity of the overall electrode. In this the fibre-based supercapacitor was constructed, the carbon was doped with manganese oxides to enhance the capacitance through introducing pseudo-capacitance at the cost of electronic conductivity. With the printing of current collectors, a highly bound electrode-current collector interface was formed, reducing the interfacial resistance and enhancing the accessible capacitance at high scan rates. In summary, this thesis presents work towards creating lower cost metal additive manufacturing through the development of an electrochemical metal 3D printer. A meniscus confined approach was taken to localise the deposition, with subsequent microstructural, mechanical and spectroscopic analysis of the printed product. Novel contributions to the field were further presented through developing understanding around multi-metal ECAM, with investigations around their coupled thermo-mechanical properties. Finally, the applicability of this approach was investigated in the field of electrochemical devices, where the influence of a porous substrate was investigated, whereby tightly bound and highly conductive current collectors were printed onto fibre based supercapacitors, enhancing their accessible capacitance. This work, therefore, demonstrates the potential for the ECAM approach in a diversity of applications.Open Acces

    Selective Resistive Sintering: A Novel Additive Manufacturing Process

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    Selective laser sintering (SLS) is one of the most popular 3D printing methods that uses a laser to pattern energy and selectively sinter powder particles to build 3D geometries. However, this printing method is plagued by slow printing speeds, high power consumption, difficulty to scale, and high overhead expense. In this research, a new 3D printing method is proposed to overcome these limitations of SLS. Instead of using a laser to pattern energy, this new method, termed selective resistive sintering (SRS), uses an array of microheaters to pattern heat for selectively sintering materials. Using microheaters offers significant power savings, significantly reduced overhead cost, and increased printing speed scalability. The objective of this thesis is to obtain a proof of concept of this new method. To achieve this objective, we first designed a microheater to operate at temperatures of 600⁰C, with a thermal response time of ~1 ms, and even heat distribution. A packaging device with electrical interconnects was also designed, fabricated, and assembled with necessary electrical components. Finally, a z-stage was designed to control the airgap between the printhead and the powder particles. The whole system was tested using two different scenarios. Simulations were also conducted to determine the feasibility of the printing method. We were able to successfully operate the fabricated microheater array at a power consumption of 1.1W providing significant power savings over lasers. Experimental proof of concept was unsuccessful due to the lack of precise control of the experimental conditions, but simulation results suggested that selectivity sintering nanoparticles with the microheater array was a viable process. Based on our current results that the microheater can be operated at ~1ms timescale to sinter powder particles, it is believed this new process can potentially be significantly quicker than selective laser sintering by increasing the number of microheater elements in the array. The low cost of a microheater array printhead will also make this new process affordable. This thesis presented a pioneering study on the feasibility of the proposed SRS process, which could potentially enable the development of a much more affordable and efficient alternative to SLS
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