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This review paper aims to introduce the inkjet printing as a tool for fabrication of flexible/wearable sensors. It summarizes inkjet printing techniques including various modes of operation, commonly used substrates and inks, commercially available inkjet printers and variables affecting the printing process. More focus is on the drop-on-demand printing mode, a strongly considered printing technique for patterning conductive lines on flexible and stretchable substrates. As inkjet-printed patterns are influenced by various variables related to its conductivity, resistivity, durability and dimensions of printed patterns, the main printing parameters (e.g. printing multilayers, inks sintering, surface treatment, cartridge specifications and printing process parameters) are reported. The embedded approaches of adding electronic components (e.g. surface-mounted and optoelectronic devices) to the stretchable circuit are also included.

In this paper, inkjet printing techniques for fabrication of flexible/stretchable circuits will be reviewed. Specifically, the various modes of operation, commonly used substrates and inks and variables affecting the printing process will be presented. Next, examples of inkjet-printed electronic devices will be demonstrated. These devices will be compared to their rigid counterpart in terms of ease of implementation and electrical behavior for wearable sensor applications. Finally, a summary of key findings and future research opportunities will be presented.

In conclusion, it is evident that the technology of inkjet printing is becoming a competitor to traditional lithography fabrication techniques, as it has the advantage of being low cost and less complex. In particular, this technique has demonstrated great capabilities in the area of flexible/stretchable electronics and sensors. Various inkjet printing methods have been presented with emphasis on their principle of operation and their commercial availability. In addition, the components of a general inkjet printing process have been discussed in details. Several factors affect the resulting printed patterns in terms of conductivity, resistivity, durability and geometry.

The paper focuses on flexible/stretchable optoelectronic devices which could be implemented in stretchable circuits. Furthermore, the importance and challenges related to printing highly conductive and highly stretchable lines, as well as reliable electronic devices, and interfacing them with external circuitry for power transmission, data acquisition and signal conditioning have been highlighted and discussed. Although several fabrication techniques have been recently developed to allow patterning conductive lines on a rubber substrate, the fabrication of fully stretchable wearable sensors remains limited which needs future research in this area for the advancement of wearable sensors.

The industry standard for applying the identification nomenclature to Printed Circuit Boards (PCBs) is silkscreen legend printing, using white ink. This multi‐step process has minimal flexibility for applying unique legends e.g. serialization numbers to individual boards. This paper describes a new, alternative single step direct legend printing system which uses piezoelectric inkjet technology, the leading digital imaging method for a variety of industrial applications. The advantages that this, inherently clean and efficient, drop‐on‐demand, printing process brings to legend printing include increased flexibility, shorter process times, good legend definition, accurate placement, small footprint equipment and reduced labour and material usage.

Recent years have seen a significant increase in the use of inkjet technology for printing on textile fabrics. Typical inkjet printed textile products included curtains, large advertising posters, flags and banners. As a result of the need for such inkjet printed products to have a greater durability, especially for outdoor applications, inks containing pigments as the colourants are gaining more interests. However, pigments may give rise to logistical problems in terms of their dispersion stability within the ink formulation, consequently blocking the nozzles within the inkjet print head. This paper reports methods for the preparation of pigment dispersions and of inkjet printing ink formulations and the methods for the evaluation of the suitability of pigmented ink formulations for jet printing on textile materials. In particular, the suitability of three magenta pigments for inkjet inks were assessed and reported.

The purpose of this paper is to present an exhaustive review of research studies and activities in the inkjet printing of conductive materials.

This paper gives a detailed literature survey of research carried out in inkjet printing of conductive materials.

This article explains the inkjet printing process and the various types of conductive inks. It then examines the various factors that affect the quality of inkjet printed interconnects such as printing parameters, materials and substrate treatments. Methods of characterising both the inkjet printing process and the electrical properties of printed conductive materials are also presented. Finally relevant applications of this technology are described.

Inkjet printing is currently one of the cheapest direct write techniques for manufacturing. The use of this technique in electronic manufacturing, where interconnects and other conductive features are required is an area of increasing relevance to the fields of electronics manufacturing, packaging and assembly. This review paper would therefore be of great value and interest to this community.

This paper aims to summarize the latest developments both in terms of theoretical understanding and experimental techniques related to inkjet fluids. The purpose is to provide practitioners a self-contained review of how the performance of inkjet and inkjet-based three-dimensional (3D) printing is fundamentally influenced by the properties of inkjet fluids.

This paper is written for practitioners who may not be familiar with the underlying physics of inkjet printing. The paper thus begins with a brief review of basic concepts in inkjet fluid characterization and the relevant dimensionless groups. Then, how drop impact and contact angle affect the footprint and resolution of inkjet printing is reviewed, especially onto powder and fabrics that are relevant to 3D printing and flexible electronics applications. A future outlook is given at the end of this review paper.

The jettability of Newtonian fluids is well-studied and has been generalized using a dimensionless Ohnesorge number. However, the inclusion of various functional materials may modify the ink fluid properties, leading to non-Newtonian behavior, such as shear thinning and elasticity. This paper discusses the current understanding of common inkjet fluids, such as particle suspensions, shear-thinning fluids and viscoelastic fluids.

A number of excellent review papers on the applications of inkjet and inkjet-based 3D printing already exist. This paper focuses on highlighting the current scientific understanding and possible future directions.

The purpose of this paper is to study the repeatability of path manufacturing in the drop on demand inkjet printing process and the influences of environmental and application factors on path resistance.

Paths were printed as multiline paths in packets one-, two- and three-layer paths on polyimide substrates using nanoparticle silver ink. The sintering conditions were determined experimentally. The paths were subjected to climatic and shock exposures and to bending processes. The resistance, profile and width of the paths were measured and analyzed. The temperature distribution for electrically heated paths was measured to identify the defects.

This research shows the repeatability of printing processes and identifies the sources that cause diversification in path parameters after the whole technological process. The influence of shock, climatic and mechanical exposures on path electrical properties is indicated. An effective method for identifying defects thermally is shown.

The research could have limited universality by arbitrarily use of substrate material, ink, printhead, process parameters and kind of sample exposures.

The research includes practically useful information about the width, thickness, defects and resistances and their changes during a typical application for a path printed with different technological parameters.

This research presents the results of original empirical research on problems concerning the manufacture of paths with uniform parameters and shows how path parameters will change under exposures that may occur in a typical application. The research combines both production and application aspects.

This paper aims to study the packing density of printed paths on different substrate materials. It presents problems which appear when the necessity of printing one or more narrow paths occurs.

A piezoelectric printhead containing nozzles with a diameter of 35 µm was used for printing nanoparticle silver ink on different polymer substrates which were treated by plasma or not treated at all. The shape, defects, resistance and printing parameters for the printed paths were analysed.

The obtained results allow the identification of the sources of the technological problems in obtaining a high packing density of the paths in a small area of substrate and the repeatable prints.

The study could have limited universality because of the chosen research method; printhead, ink, substrate materials and process parameters were arbitrarily selected. The authors encourage the study of other kinds of conductive inks, treatment methods and printing process parameters.

The study includes practically useful information about widths, shapes, defects and the resistance of the paths printed using different technological parameters.

The study presents the results of original empirical research on problems of the packing density of inkjet printed paths on a small area of substrate and identifies problems that must be resolved to obtain effective interconnections in the inkjet technology.

This paper aims to encompass the technological advancements in the area of flexible sensing electronics fabrication particularly for wearable device development applications. In the recent past, it is evident that there is a tremendous growth in the field of flexible electronics and sensors fabrication technologies all around the world. Even though, there is a significant amount of research has been carried in the past decade, but still there is a huge need for exploring novel materials for low temperature processing, optimized printing methods and customized printing devices with accurate feature control.

The author has done an extensive literature survey in the proposed area and found that the researchers are showing significant interest in exploring novel materials, new conductive ink processing methods suitable for additive manufacturing, and fabrication technologies for developing the plastic substrate-based flexible electronics for the on growing demands of wearable devices in the market.

The author has consolidated some of the recent advancements in the area of flexible sensing electronics using the inkjet-printing platform carried out by the researchers. The novel customized inkjet-printing technology, materials selections for device development, compatibility of the materials for the inkjet-printing process and the interesting results of the devices fabricated are highlighted in this paper.

The author has reported the novel inkjet-printing platforms explored by researchers in the recent past for various applications which primarily includes gas sensing. The author has consolidated in a crisp manner about the technology, materials compatible for inkjet-printing, and the exciting results of the printed devices. The author has reported the advantages and challenges of the proposed methods by the researchers. This work will bridge the technical gap in the inkjet-printing technology and will be useful for the researchers to take forward the research work on this domain to the next level.

To review opportunities for use of digital printing in the printed circuit board (PCB) industry and to introduce background to ink jet printing, process development and applications in order to reduce costs, enhance efficiency and to enable PCB producers to operate in a more sustainable and flexible manner.

This paper has been written to provide a review of ink jet printing applications in the PCB industry. Ink jet print technology background, ink development and the processes made possible by ink and print head improvements have been described together with a description of the benefits available through digital printing.

It was found that there have been significant developments over recent years in both hardware technology (print heads and accurate print platforms) as well as improvements in the design of inks both for ink jet print performance and functional characteristics. These improvements have been integrated to provide an exciting new technology which can be applied in the manufacture of PCBs to reduce manufacturing costs and increase flexibility of manufacture.

The value of the paper lies in its ability to provide information on the scope of opportunities for ink jet printing in the PCB manufacturing process through the use of a range of new inks having specific properties. The design and development of highly accurate machinery provides the opportunity to attain the desired print resolution.

This paper aims to present a requirements analysis for the processing of water-based electrode dispersions in inkjet printing.

A detailed examination of the components and the associated properties of the electrode dispersions has been carried out. The requirements of the printing process and the resulting performance characteristics of the electrode dispersions were analyzed in a top–down approach. The product and process side were compared, and the target specifications of the dispersion components were derived.

Target ranges have been identified for the main component properties, balancing the partly conflicting goals between the product and the process requirements.

The findings are expected to assist with the formulation of electrode dispersions as printing inks.

Little knowledge is available regarding the particular requirements arising from the systematic qualification of aqueous electrode dispersions for inkjet printing. This paper addresses these requirements, covering both product and process specifications.