Conductive Ink Printing Research Articles

Optimization of trajectory processing algorithms to print 3D circuit boards using piezo ink jet and 6-axis robots

Direct printing of conductive inks at the surface of generic 3D objects using 6 axis robots is attracting an ever-increasing interest, however the high precision positioning and the generation of smooth printing trajectories still represent a bottleneck for the manufacturing of 3D electronic circuits. This work presents a new approach for the rapid prototyping of 3D electronics onto generic objects using a 6 axis robot equipped with a piezo jetting printhead and a high speed laser profiler and a six steps protocol composed by the: i) 3D scan of the substrate and mesh smoothing, ii) 2D circuit projection on the planarized mesh and generation of the 3D trajectory, iii) normals alignment of points lying in the 3D trajectory, iv) retrieve of the effective toolhead TCP translation speed along the 3D trajectory with a blank run, v) synchronization of the ink jetting frequency with the effective toolhead speed, vi) generation of the robot code and print.The effect of mesh and normals smoothing and of circuit design on the effective toolhead translation speed was systematically investigated in order to minimize speed fluctuations/heterogeneous ink deposition during printing, the computational load and shape deviation from the pristine 3D substrate.Conductive tracks printed on an ABS dome displayed geometry and line resistance in line with those predicted by a semi-empirical model using the robot nominal speed and silver ink conductivity, thus showing that the robot operated under stable and well controlled conditions during the printing process.The developed process displayed an average duty cycle of ca. 30 min from the 3D scan to the printing of the 3D circuit, thus showing that it could be suitable for the rapid prototyping/benchmarking of 3D electronics on generic objects.

E-Textile by Printing an All-through Penetrating Copper Complex Ink.

Wearable electronics is an emerging field in academics and industry, in which electronic devices, such as smartwatches and sensors, are printed or embedded within textiles. The electrical circuits in electronics textile (e-textile) should withstand many cycles of bending and stretching. Direct printing of conductive inks enables the patterning of electrical circuits; however, while using conventional nanoparticle-based inks, printing onto the fabric results in a thin layer of a conductor, which is not sufficiently robust and impairs the reliability required for practical applications. Here, we present a new process for fabricating robust stretchable e-textile using a thermodynamically stable, solution-based copper complex ink, which is capable of full penetrating the fabric. After printing on knitted stretchable fabrics, they were heated, and the complex underwent an intermolecular self-reduction reaction. The continuously formed metallic copper was used as a seed layer for electroless plating (EP) to form highly conductive circuits. It was found that the stretching direction has a significant role in resistivity. This new approach enables fabricating e-textiles with high stretchability and durability, as demonstrated for wearable gloves, toward printing functional e-textile.

Inkjet-Printed Polyelectrolyte Seed Layer-Based, Customizable, Transparent, Ultrathin Gold Electrodes and Facile Implementation of Photothermal Effect

Recently, interest in transparent electrodes has been increasing in biomedical engineering applications for such as electro-optical hybrid neuro-technologies. However, conventional photolithography-based electrode fabrication methods have limited design customization and large-area applicability. For biomedical engineering applications, it is crucial that we can easily customize the electrode design for different patients over a large body area. In this paper, we propose a novel method to fabricate customization-friendly, transparent, ultrathin, gold microelectrodes using inkjet printing technology. Unlike with typical direct printing of conductive inks, we inkjet-printed a polymer nucleation-inducing seed layer, followed by mask-less vacuum deposition of ultrathin gold (<6 nm) to produce selectively, high-transparency electrodes in the predefined shapes of the inkjet-printed polymer. Owing to the design flexibility of inkjet printing, the transparent ultrathin gold electrodes can be highly efficient in design customization over a large area. Simultaneously, a layer of nonconductive gold islands is formed in the nonprinted region, and this nanostructured layer can implement a photothermal effect that offers versatility for novel biomedical applications. As a demonstration of the effectiveness of these transparent electrodes, and the facile implementation of the photothermal effect for biomedical applications, we successfully fabricated transparent resistive temperature detectors. We used these to directly sense the photothermal effect and to demonstrate their bioimaging capabilities.

Biodegradable Cellulose Nanocomposite Substrate for Recyclable Flexible Printed Electronics

AbstractPrinted, flexible, and hybrid electronic technologies are advancing rapidly leading to remarkable developments in smart wearables, intelligent textiles, and health monitoring systems. Flexible electronics are typically fabricated on petroleum‐derived polymeric substrates. However, in the light of global environmental concerns regarding fossil raw materials, there is a need to drive the production of flexible electronics devices based on sustainable materials. Additionally, there is a need to reduce the quantity of electronic waste by developing material recovery and recycling technologies. Here, a fully biobased and biodegradable substrate tailored for printed flexible electronic applications is developed. Based on a nanocomposite of cellulose nanofibril (CNF) and hydroxyethyl cellulose (HEC), the substrate shows excellent mechanical and optical properties for printed flexible electronics applications. High‐resolution screen printing of conductive ink and typical electronics assembly processes are possible to realize on the substrate. An electrocardiograph (ECG) device is fabricated on the cellulosic substrate as a technology demonstrator and its performance is confirmed on human volunteers. Last, end‐of‐life scenarios are studied for printed electronic devices where device degradation and subsequent material recovery concepts are presented. This work demonstrates that sustainable plant‐derived materials can play a big role toward a green transition in the electronics industry.

Extrusion-Based 3D Printing of Stretchable Electronic Coating for Condition Monitoring of Suction Cups.

Suction cups (SCs) are used extensively by the industrial sector, particularly for a wide variety of automated material-handling applications. To enhance productivity and reduce maintenance costs, an online supervision system is essential to check the status of SCs. This paper thus proposes an innovative method for condition monitoring of SCs coated with printed electronics whose electrical resistance is supposed to be correlated with the mechanical strain. A simulation model is first examined to observe the deformation of SCs under vacuum compression, which is needed for the development of sensor coating thanks to the 3D printing process. The proposed design involves three circle-shaped sensors, two for the top and bottom bellows (whose mechanical strains are revealed to be the most significant), and one for the lip (small strain, but important stress that might provoke wear and tear in the long term). For the sake of simplicity, practical measurement is performed on 2D samples coated with two different conductive inks subjected to unidirectional tensile loading. Graphical representations together with analytical models of both linear and nonlinear piezoresistive responses allows for the characterization of the inks’ behavior under several conditions of displacement and speed inputs. After a comparison of the two inks, the most appropriate is selected as a consequence of its excellent adhesion and stretchability, which are essential criteria to meet the target field. Room temperature extrusion-based 3D printing is then investigated using a motorized 3D Hyrel printer with a syringe-extrusion modular system. Design optimization is finally carried out to enhance the surface detection of sensitive elements while minimizing the effect of electrodes. Although several issues still need to be further considered to match specifications imposed by our industrial partner, the achievement of this work is meaningful and could pave the way for a new generation of SCs integrated with smart sensing devices. The 3D printing of conductive ink directly on the cup’s curving surface is a true challenge, which has been demonstrated, for the first time, to be technically feasible throughout the additive manufacturing (AM) process.

Aerosol printing and flash sintering of conformal conductors on 3D nonplanar surfaces

Printing techniques have been extensively studied as a promising route towards large-scale, low-cost and high-throughput manufacturing process for electronic devices. With the recently emerging applications in wearable electronics and customizable conformal electronics, it calls for the necessity to develop printed electronics that function on complex, 3D nonplanar architectures. In this study, aerosol printing and flash sintering of conformal conductors on nonplanar surfaces are demonstrated. Various printed patterns are fabricated by aerosol printing of conductive ink by copper nanoparticles (Cu NPs) on both planar and nonplanar surfaces. Pulsed flash light introduces rapid sintering of the printed Cu patterns in the ambient environment. For the nonplanar patterns, a back reflector is utilized to improve the uniformity of sintering. As a result, highly conductive customizable nonplanar Cu patterns with conductivity at 10%–12% of that of bulk Cu are obtained. Effects of different sintering conditions, including sintering voltage and mounting distance on the conductivity of sintered patterns are studied. For nonplanar patterns, conductivity values at different localized spots on the nonplanar rod are also investigated to evaluate the uniformity of nonplanar sintering. The processes of aerosol printing and flash sintering have provided a facile manufacturing route for conformal conductors on arbitrary nonplanar objects.

High resolution electrohydrodynamic printing of conductive ink with an aligned aperture coaxial printhead

High resolution electrohydrodynamic printing of conductive ink with an aligned aperture coaxial printhead

3D Particle Free Printing of Biocompatible Conductive Hydrogel Platforms for Neuron Growth and Electrophysiological Recording.

Electrically conductive 3D periodic microscaffolds are fabricated using a particle-free direct ink writing approach for use as neuronal growth and electrophysiological recording platforms. A poly (2-hydroxyethyl methacrylate) (pHEMA)/pyrrole ink, followed by chemical in situ polymerization of pyrrole, enables hydrogel printing through nozzles as small as 1 μm. These conductive hydrogels can pattern complex 2D and 3D structures and have good biocompatibility with test cell cultures (~94.5% viability after 7 days). Hydrogel arrays promote extensive neurite outgrowth of cultured Aplysia californica pedal ganglion neurons. This platform allows extracellular electrophysiological recording of steady-state and stimulated electrical neuronal activities. In summation, this 3D conductive ink printing process enables preparation of biocompatible and micron-sized structures to create customized in vitro electrophysiological recording platforms.

Printing accuracy tracking with 2D optical microscopy and super-resolution metamaterial-assisted 1D terahertz spectroscopy

Printable electronics is a promising manufacturing technology for the potential production of low-cost flexible electronic devices, ranging from displays to active wear. It is known that rapid printing of conductive ink on a flexible substrate is vulnerable to several sources of variation during the manufacturing process. However, this process is still not being subjected to a quality control method that is both non-invasive and in situ. To address this issue, we propose controlling the printing accuracy by monitoring the spatial distribution of the deposited ink using terahertz (THz) waves. The parameters studied are the printing speed of an industrial roll-to-roll press with flexography printing units and the pre-calibration compression, or expansion factor, for a pattern printed on a flexible plastic substrate. The pattern, which is carefully selected, has Babinet’s electromagnetic transmission properties in the THz frequency range. To validate our choice, we quantified the geometric variations of the printed pattern by visible microscopy and compared its accuracy using one-dimensional THz spectroscopy. Our study shows a remarkable agreement between visible microscopic observation of the printing performance and the signature of the THz transmission. Notably, under specific conditions, one-dimensional (1D) THz information from a resonant pattern can be more accurate than two-dimensional (2D) microscopy information. This result paves the way for a simple strategy for non-invasive and contactless in situ monitoring of printable electronics production.

Electrohydrodynamic jet printing for desired print diameter

Advent of flexible sensor technology necessitates micro-additive manufacturing for printing of conductive inks on flexible substrate. Electrohydrodynamic (EHD) jet printing, being one of such micro additive manufacturing methods, is under research boost, now-a-days. In EHD printing very fine drops can be deposited on the substrate surface with the help of applied electric field, so that the electric field parameters can be regulated to vary the size of the printed drops. Thus, there is more flexibility in EHD printing, as compared with other micro additive manufacturing, for achieving the targeted print width (line printing) or printed drop diameter (dot printing). However, there are five controllable process parameters (excluding nozzle, ink, substrate, and post printing parameters), selection of which is very challenging to achieve the expected print diameter. Thus, in this work, an attempt has been made to print silver nanoparticle on glass substrate by EHD jet printing for achieving 140 μm diameter dots from a capillary nozzle of 840 μm inner diameter. Three parameters (out of five) i.e., voltage, pulse frequency and duty ratio has been selected analytically to achieve the targeted print diameter. Finally, printing of silver dots with 145 μm to 165 μm diameter has been achieved, in this work.

Preparation of Printable and Biodegradable Cellulose-Laponite Composite for Electronic Device Application

Printable and biodegradable printed circuit boards (PCBs) prepared by using cellulose as the continuous matrix, laponite as flame retardant filler with various weight ratio (0, 5, 10 and 20 wt% with respect to the α-cellulose quantity used to prepare the composites) and 1-ethyl-3-methylimidazolium acetate ([emim][OAc]) as the recoverable dissolution medium. Prepared cellulose-composites were subjected into physical, chemical, thermal, mechanical and biodegradation analyses to check the suitability of the cellulose-laponite composite for biodegradable electronic application. The addition of laponite into cellulose increased the degradation temperature, flame retardancy and decreased the mechanical properties of the cellulose-laponite composites. The surface nature of the cellulose composite converted from hydrophilic to hydrophobic (contact angle value increased in the range from 50° to 112°) by treating with relatively small amount of hydrophobizing agent (< 1 wt%). The conductive ink printing experiments on the composites explaining the role of hydrophobizing agent and laponite in the composites. Biodegradability of the cellulose was evaluated by enzyme treatments and derived the effect of laponite, hydrophobic agent and conductive ink.

Electronic Component Mounting for Durable E-Textiles: Direct Soldering of Components onto Textile-Based Deeply Permeated Conductive Patterns.

For the improvement of the performance and function of electronic textiles (e-textiles), methods for electronic component mounting of textile circuits with electrical and mechanical durability are necessary. This manuscript presents a component mounting method for durable e-textiles, with a simpler implementation and increased compatibility with conventional electronics manufacturing processes. In this process, conductive patterns are directly formed on a textile by the printing of conductive ink with deep permeation and, then, components are directly soldered on the patterns. The stiffness of patterns is enhanced by the deep permeation, and the enhancement prevents electrical and mechanical breakages due to the stress concentration between the pattern and solder. This allows components to be directly mounting on textile circuits with electrical and mechanical durability. In this study, a chip resistor was soldered on printed patterns with different permeation depths, and the durability of the samples were evaluated by measuring the variation in resistance based on cyclic tensile tests and shear tests. The experiments confirmed that the durability was improved by the deep permeation, and that the samples with solder and deep permeation exhibited superior durability as compared with the samples based on commercially available elastic conductive adhesives for component mounting. In addition, a radio circuit was fabricated on a textile to demonstrate that various types of components can be mounted based on the proposed methods.

Properties enhancement of graphene and chemical reduction silver nanoparticles conductive inks printed on polyvinyl alcohol (PVA) substrate

Inkjet printing of conductive ink on flexible substrates is emerging as an attractive technology for wide variety applications. In this study, graphene and silver nanoparticles (AgNPs) conductive inks were printed on polyvinyl alcohol (PVA) substrates by inkjet printer. Effect of different solvents, printing cycles and annealing time on the performance of conductive ink was investigated. Three different groups of solvents were used to prepare the conductive ink; deionized water (DI): ethylene glycol (EG): glycol (G), isopropyl alcohol (IA): ethylene glycol (EG): glyceol (G) and dimethylformamide (DMF): Ethylene glycol (EG): Glyceol (G). DMF: EG: G solutions produced conductive ink with higher stability, wettability and electrical conductivity compared to other conductive ink formulations. It was observed that increased of printing cycles (from 1 to 5) times and annealing time (from 0 to 30) min had increase the electrical conductivity. During stretching, graphene conductive ink on PVA substrate shows lower electrical conductivity reduction compared to that of AgNPs conductive ink. Flaky shape of graphene able to maintain the conductive paths under loading condition.

High electrical conductivity waterborne inks for textile printing

Printing of conductive inks is an attractive means of manufacturing of electronic components on flexible substrates including textiles. The textiles thus produced are often referred to as “e-textiles.” When high electrical conductivity is required, inks are preferably made from metal nanoparticles such as silver. However, such inks are expensive and generally not known to withstand severe washing and wearing to which textiles are normally subjected during the end use. In the present study, which forms a part of a larger study by the authors, waterborne dispersions of conductive grades of carbon black were converted into finished inks followed by washing and creasing tests to ascertain the durability of these inks. We found that not only were the inks stable after letdown with different binders, but they possessed high electrical conductivity despite the fact that the final pigment loading in all of the formulated inks was significantly less than the pigment loading that is generally found in commercial conductive inks. In addition, the electrical conductivity after washing and creasing tests of the formulated inks was found to be significantly greater than that of the tested commercial conductive inks. This shows that using large surface area, highly conductive grades of carbon black pigments in relatively small amounts in inks for textile printing is beneficial in achieving some of the critically required characteristics, particularly those pertaining to durability of the ink film.

Recent Advancements in Wearable &amp; Smart Textiles: An Overview

Abstract Smart wearable textile’ becomes a major segment of electronic-textiles (e-textiles) along with smart clothing and information science (wearable computer). Wearable textiles can sense, react and adapt themselves accordingly to external conditions or stimuli and wearable textiles can be divided into active and passive smart wearable textiles which can be work with human brain with cognition, reasoning, activating capacity. Generally, different unsaturated polymeric substrates as polyaniline, polypyrrole, polytiophene and polyacetylene are used as inherently conductive materials. Now these day single/ multiwalled-nano carbon tubes (SWCNT/MWCNT) and Ag, Cu, Au nanoparticles are used as e-textiles basic yarn materials with variable cross sectional areas (sandwiched, coated, shelled, tri-lobal or twisted forms). Their conductivity ranges can varies within 10-1-10-8-cm-1. The products are assorted with a varieties of depth as centrally controlled sensors, actuators, circuit tree added conductive stitched or embroidered fabric, planer electric yarn, data transferring devices, conductive ink printing, textile Bluetooth antenna, integrated fabric area networked clothing, EMI shielding, power supply clothing, Numetrex sports bra (Textronics), intelligence textile wears like WarmX vest, textile headband for facial EMG and knee sleeve and flex sensor or even as pressure sensor providing relief from post-medical operational health risk hazards. e-textiles can be used in military applications in detection of enemies or biochemical threats. Recently developed ‘Biodegradable Smart Shirt’ textile platform is also able to monitor vital signs and heartbeats or palpitation rates for the patient using data management based information applications. Wearable e-textile has been introduced to fashion articles, for example: ICD+ Jacket with fabricated embroidered textile keypad or improvised to Softswitch remote control and light switch and pillow covers (made by Phillips Electronics and Levi Strauss) which can perform multiple modalities of works like mobile connect, geo-navigation and MP3 players as per the consumer’s choices. This paper particularly aims to review all the latest developments of wearable e-textiles.

Spraying dynamics in continuous wave laser printing of conductive inks

Laser-induced forward transfer (LIFT), though usually associated with pulsed lasers, has been recently shown to be feasible for printing liquid inks with continuous wave (CW) lasers. This is remarkable not only because of the advantages that the new approach presents in terms of cost, but also because of the surprising transfer dynamics associated with it. In this work we carry out a study of CW-LIFT aimed at understanding the new transfer dynamics and its correlation with the printing outcomes. The CW-LIFT of lines of Ag ink at different laser powers and scan speeds revealed a range of conditions that allowed printing conductive lines with good electrical properties. A fast-imaging study showed that liquid ejection corresponds to a spraying behavior completely different from the jetting characteristic of pulsed LIFT. We attribute the spray to pool-boiling in the donor film, in which bursting bubbles are responsible for liquid ejection in the form of projected droplets. The droplet motion is then modeled as the free fall of rigid spheres in a viscous medium, in good agreement with experimental observations. Finally, thermo-capillary flow in the donor film allows understanding the evolution of the morphology of the printed lines with laser power and scan speed.

Overview of printing wearable antenna

The usage of wearable textiles in antenna section has been seen increased due to the advanced in miniaturization of wireless devices. A wearable antenna is meant to be a part of the clothing and body used for communication purposes, which includes tracking and navigation, mobile computing and public safety. Printing of conductive ink gives the leisure of flexibility properties on electronics thus allowing it to be used on conformal surfaces such as textiles. However, the current printing techniques mostly suffer from ink incompatibility and limited of substrates to be printed with. Hence, this paper discusses an overview of conventional and current printing techniques of wearable antenna and a potential of automatic syringe deposition system to print electronics structure mainly antenna using conductive ink on conformal substrates particularly textiles.

Printing of Wearable Antenna on Textile

A wearable antenna which is meant to be a part of the clothing used for communication purposes includes tracking, navigation and mobile computing has been seen in demand due to the recent miniaturization of wireless devices. Printing of conductive ink provides flexibility properties on electronics thus allowing it to be used on conformal surfaces. However, the current printing techniques mostly suffer from ink incompatibility and limited of substrates to be printed with. Hence, this paper intend to discloses the printing of wearable antenna using alternative technique via syringe-based deposition system with conductive ink on textile. A validation between simulation and measurement of return loss, (S11) and radiation pattern of the antenna printed is also performed. It was found that a functional antenna is successfully printed on textile since the performances obtained are as expected. The antenna resonated at a minimum resonant frequency of 1.82 GHz which the S11 gathered at-18.90 dB. The radiation pattern for both simulation and measurement is as predicted since both have a larger magnitude of the main lobe than the side lobe. The magnitude of the main lobe from measurement was observed to be 8.83 dB higher than the magnitude of the main lobe of the simulation which is only 3.77 dB. It is proven that the syringe-based deposition system is capable of printing functional antenna on textile.

Interlaminar Magnetic Flux Assessment of a Transformer Core Measured by an Extra-Thin Printed Foil Detector

Transformer cores represent complex 3-D magnetization systems with balancing off-plane fluxes, normal to magnetization plane. Therefore, for optimizations of core performance, not only the information about the local induction distributions in the plane, but also perpendicular to it is highly essential. The conventional sensors for detections of off-plane inductions $B_{Z}$ ( ${t}$ ) are either of very high thicknesses, causing significant air gaps between laminations, or require extremely laborious preparations and are not reusable. In this paper, we developed an extra-thin ( $\approx 50~\mu \text{m}$ ), reusable foil detector with handles for easy and precise insertion and positioning in the interior of a laminated core. The detector was assembled by a low-cost 3-D printer, equipped with a micro-dispersing system for printing of conductive ink, controlled by in-house developed software. The manufactured foil sensor, due to its high mechanical stability, enables detections of off-plane flux at many different locations within an entire core. The detector was effectively tested in a three-phase model transformer core, stacked from three packages of different width. The results prove the important role of sensor thickness for precise detection of off-plane induction. Peak induction $B_{Z}$ increases in a strong non-linear way with increasing nominal magnetization $B_{\mathrm{ NOM}}$ . Maxima of $B_{Z}$ arise close to border regions of packages. $B_{Z}$ ceases for $B_{\mathrm{ NOM}} T, favoring low level of audible noise.

Manufacturing of a failure detection sensor for POM spur gears based on printing of conductive ink

Manufacturing of a failure detection sensor for POM spur gears based on printing of conductive ink