Optimisation of substrate angles for multi-material and multi-functional inkjet printing

Three dimensional inkjet printing of multiple materials for electronics applications are challenging due to the limited material availability, inconsistencies in layer thickness between dissimilar materials and the need to expose the printed tracks of metal nanoparticles to temperature above 100 °C for sintering. It is envisaged that instead of printing a dielectric and a conductive material on the same plane, by printing conductive tracks on an angled dielectric surface, the required number of silver layers and consequently, the exposure of the polymer to high temperature and the build time of the component can be significantly reduced. Conductive tracks printed with a fixed print height (FH) showed significantly better resolution for all angles than the fixed slope (FS) sample where the print height varied to maintain the slope length. The electrical resistance of the tracks remained under 10Ω up to 60° for FH; whereas for the FS samples, the resistance remained under 10Ω for samples up to 45°. Thus by fixing the print height to 4 mm, precise tracks with low resistance can be printed at substrate angles up to 60°. By adopting this approach, the build height “Z” can be quickly attained with less exposure of the polymer to high temperature

Electrical Sintering of Silver Nanoparticle Ink Studied by In-Situ TEM Probing

Metallic nanoparticle inks are used for printed electronics, but to reach acceptable conductivity the structures need to be sintered, usually using a furnace. Recently, sintering by direct resistive heating has been demonstrated. For a microscopic understanding of this Joule heating sintering method, we studied the entire process in real time inside a transmission electron microscope equipped with a movable electrical probe. We found an onset of Joule heating induced sintering and coalescence of nanoparticles at power levels of 0.1–10 mW/m3. In addition, a carbonization of the organic shells that stabilize the nanoparticles were found, with a conductivity of 4 105 Sm−1

The sea voyage as a marriage snare: gender in novels about the passage between the Netherlands and the Dutch East Indies (1869–1891)

Medieval and Early Modern Studie

Surface Treatments for Inkjet Printing onto a PTFE-Based Substrate for High Frequency Applications

This document is the Accepted Manuscript version of a Published Work that appeared in final form in the journal Industrial and Engineering Chemistry Research [copyright © American Chemical Society] after peer review and technical editing by the publisher. To access the final edited and published work see: http://pubs.acs.org/doi/abs/10.1021/ie4006639Inkjet printing onto laminates for use in high frequency applications (high frequency laminates) is challenging, due to the substrate surface roughness present after etching away the copper layer(s). This has a detrimental effect on interconnect losses as the frequency increases. In this paper, different surface treatments to reduce the surface roughness of a typical high frequency laminate (RO3006) are investigated. In particular, the importance of matching the substrate surface energy to the ink to achieve a smooth coated layer for the case of a UV cured insulator is demonstrated. This is achievable within the parameters of heating the platen, which is a more flexible approach compared to modifying the ink to improve the ink-substrate interaction. In printing onto the surface modified substrates, the substrate roughness was observed to affect the printed line width significantly. A surface roughness factor was introduced to take into account the phenomenon by modifying the original formula of Smith et al. Lastly, the authors show that the printed line widths are also influenced by the surface tension arising from charges present on the surface modified substrates

The effect of droplet ejection frequency on the dimensions of inkjet-etched micro-via holes in poly4(-vinyl phenol) thin films

This article was published in the Journal of Physics D: Applied Physics [© IOP Publishing Ltd] and the definitive version is available at: http://dx.doi.org/10.1088/0022-3727/45/12/125303The relationship between the size of inkjet-etched via-holes produced in poly4(-vinyl phenol) thin films and the number of ethanol drops dispensed was established for a range of droplet ejection frequencies. The physical mechanism underlying this relationship is proposed and the dependence of the development of via-hole dimensions on the droplet ejection frequency is believed to be attributable to the extent of evaporation of the solvent between two consecutive drop dispenses. The results indicate complete penetration of the via-holes through the polymer layer when produced at low droplet ejection frequencies. Electroplating was used to deposit Cu into the created holes to further confirm the absence of polymer residue at low frequencies. A threshold frequency, under which no via-hole enlargement occurs, has been found. The study systematically focuses on the influence of droplet ejection frequency on the size of the inkjet-etched via-holes versus the number of droplets used in poly4(-vinyl phenol) dielectric thin films for printed electronics application

Microstructures prepared via inkjet printing and embossing techniques

The goal of the work presented in this thesis is the combined use of inkjet printing and embossing techniques to fabricate microstructures. The thesis is divided into two sections. The first part (Chapters 1 to 4) describes a bottom-up procedure using inkjet printing to fabricate microstructures onto polymeric substrates, whereas the second part (Chapters 5 and 6) describes hot-embossing and a new technique called photo-embossing for the creation of surface relief structures, that are filled using an inkjet printer to improve resolution. The introduction offers a literature survey that describes the history and recent achievements in the inkjet printing field. Inkjet printing has developed from only producing text and graphics into a major topic in current research and development. Chapter 2 describes the behaviour of ink droplets both in-flight as well as upon impinging the substrate, which are discussed in order to understand the basics of successful inkjet printing. For equally-sized droplets of a dilute polystyrene solution, a linear relationship, which decreased, was observed between the dried droplet diameter and the printing height. Whereas, increased concentrations revealed an initial exponential decay in the dried droplet diameter, which stabilized at greater heights. At higher concentrations and heights, the polymer is believed to form a skin on the surface of the inkjet printed droplet, which causes inhibition of the in-flight evaporation of the solvent. The size-selective segregation of monodisperse silica particles in drying droplets was also studied. It was observed that the particles sediment as close as possible towards the periphery; the actual distance between the location of segregated particles and the contact line increases with increasing particle size. The third chapter describes inkjet printing of functional materials. A polyurethane dispersion was inkjet printed to fabricate three-dimensional structure with single layers having a height of approximately 10 µm. Secondly, an aqueous TiO2 nanoparticle ink was printed that gels above a certain temperature. Droplets and lines with improved morphological control and resolution were achieved using this thermal gelation effect. Defect-free straight lines could be printed on hydrophobic surfaces, which is impossible with regular inks due to the dewetting nature of these substrates. Finally, the resolution of directly inkjet printed lines of silver nanoparticles on polymer substrates that have a lower surface energy than common polymer substrates was improved: lines with a resolution down to 40 µm were printed. After depositing silver nanoparticle inks, a thermal sintering step is required in order to render the particles conductive, which is discussed in Chapter 4. Polymer substrates can usually not withstand high temperatures and, therefore, require a low temperature during the sintering process. Two new techniques are discussed that sinter in a selective way so that the polymer substrate is not affected. These techniques are exposure to microwave radiation and argon plasma. With the former technique, the sintering time was shortened by a factor of 20 and three minutes were sufficient for sintering. Furthermore, the presence of conductive antennae further promotes sintering and times of 1 second are sufficient to obtain pronounced nanoparticle sintering. The second technique uses exposure to argon plasma; a process that shows a clear evolution starting from a sintered top layer into bulk material. Chapter 5 describes a new technique called photo-embossing. This method represents a photolithographic technique for the generation of polymer relief structures that are created by a deformation of the surface of the film, which is caused by a material flux induced by a local polymerization. One of the main problems in photo-embossing is the low aspect ratio of the formed features. Chapter 5 describes the improvement of the aspect ratio by adding compounds that interfere with the reaction kinetics, such as t-butyl hydroquinone (TBHQ) and reversible addition-fragmentation chain transfer (RAFT) agents. By adding these compounds the aspect ratios were significantly improved up to a factor of almost 10. The last chapter describes the inkjet printing of a silver nanoparticle ink onto a predefined topography pattern in a thermoplastic surface. These topographical structures have been embossed into the polymer surface. Subsequently, droplets of a silver nanoparticle ink were dispensed over the asformed micro-channels. As a consequence of capillary forces the micro-channels were filled with the ink and tracks with an improved resolution were formed. The silver tracks had widths ranging from 5 to 25 µm. In general, it can be concluded that inkjet printing represents a highly suitable technique for systematic and statistical studies, since multiple equally sized droplets can be dispensed into a matrix, which subsequently can be analysed. Furthermore, inkjet printing is capable of preparing highresolution conductive features on or into polymer substrates. Together with inkjet printing, (ink) materials can be saved, since the ink is only dispensed on demand. It is, however, necessary to tune the polymer substrate as well the conductive inks properties. Alternative and selective sintering methods open new routes to produce conductive features on common polymer foils that have a relatively low glass transition temperature. In combination with different embossing techniques inkjet printing could lead to a higher resolution and more continuous overall processing of electronic devices on flexible substrates in the future. The improved photo-embossed structures offer a simple and versatile alternative for the production of large-scale/large-area relief structures in thin polymer films

Reactive inkjet printing of polyurethanes

Reactive inkjet printing technology was used to create micron-scale polyurethane structures, such as dots, lines and pyramids. These structures were fabricated insitu and cured within five minutes by inkjet printing two separate inks successively from two separate print heads, with one ink containing isophorone diisocyanate, and the other consisting of an oligomer of poly(propylene glycol), a catalyst, and a cross-linking agent. The fast polymerization reaction that forms polyurethane at the surface opens a new route for rapid prototyping, as well as the use of inkjet printing as a technique for handling moisture-sensitive reactions. By the addition of fluorescent dyes to the polyol ink, confocal laser scanning fluorescence microscopy was used to investigate the miscibility behavior of both solutions on the substrate