Conductive Tracks Research Articles

Research on Printed Conductive Silver Layer based on Inkjet Photo Paper

Printed electronics is an emerging technology that applies traditional printing or coating processes to the manufacture of electronic devices and products. In order to find a low-cost, high-performance, environmentally-friendly flexible substrate suitable for electronic devices, the printability between four kinds of inkjet photo papers and nano-silver ink was investigated. First, different surface morphologies of the inkjet photo papers were measured by a confocal laser scanning microscopy. Then, a pen and a gravure printer were used to test the printability between photo papers and nano-silver ink. It was found that the conductive track and pattern was influenced by the surface morphology of the photo papers. Furthermore, a four-probe test showed that the conductivity of the ink layers on the four photo papers was almost at the same level. Furthermore, a tearing test with 3 M tapes showed that the silk photo paper had the best tearing resistance. In general, silk photo paper has the best overall performance. This research could be beneficial for the development of flexible electronic devices which are low-cost, mass manufacture suitable and environment friendly.

Post-printing characterisation and design for additive manufacturing considerations for conductive tracks 3D-printed by material extrusion

Post-printing characterisation and design for additive manufacturing considerations for conductive tracks 3D-printed by material extrusion

Post-printing Characterisation and Design for Additive Manufacturing Considerations for Conductive Tracks 3D Printed by Material Extrusion

Post-printing Characterisation and Design for Additive Manufacturing Considerations for Conductive Tracks 3D Printed by Material Extrusion

Inkjet printing of silver nanowires on flexible surfaces and methodologies to improve the conductivity and stability of the printed patterns.

Silver nanowires (AgNWs) are known to be used for printing on rigid as well as flexible surfaces. Here we have developed a systematic approach for using AgNWs synthesized by the polyol method for printing on flexible surfaces using a simple inkjet printing method. Optimized ink formulation used in this work comprises a mixture of Ag NWs suspended in ethylene glycol directly taken after synthesis and isopropyl alcohol. Using such formulation saves time and loss of material while transferring to other solvents, which is the usual practice. The printed patterns demonstrate high conductivity and stability over many months, which can revolutionize the applications of functional nanomaterials in low-cost printed electronics. The importance of fragmentation of nanowires only to achieve specific aspect ratios, to facilitate easy jetting and to prevent clogging is demonstrated. Varied concentrations (10 mg mL−1 to 50 mg mL−1) of Ag NWs are used in ink formulations in order to print highly conductive patterns (resistance < 50 Ω sq−1) in a minimal number of passes. The same composition was also seen to facilitate simple and time-efficient nano-welding at room temperature, which improves the conductivity and stability of the printed patterns.

Chemical inspection and elemental analysis of electronic waste using data fusion - Application of complementary spectroanalytical techniques

This study is focused on the development of analytical methods for characterization of printed circuit boards (PCBs) from mobile phones by direct analysis using three complementary spectroanalytical techniques: laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), laser-induced breakdown spectroscopy (LIBS), and micro X-ray fluorescence spectroscopy (micro-XRF). These techniques were combined with principal component analysis (PCA) to investigate the chemical composition on the surface and depth profiling of PCB samples. The spatial distribution of important base metals (e.g. Al, Au, Ba, Cu, Fe, Mg, Ni, Zn), toxic elements (e.g. Cd, Cr, Pb) as well as the non-metallic fraction (e.g. P, S and Si) from conductive tracks, solder mask and integrated components were detected within the PCB samples. Univariate and multivariate approaches were also performed to obtain calibration models for Cu determination. The results were compared to reference concentrations obtained by inductively coupled plasma-optical emission spectrometry (ICP-OES) after microwave-assisted acid leaching using aqua regia. To this end, two PCB samples (50 × 34 mm2) were cut into small parts of 40 subsamples (10 × 8.5 mm2) and analyzed by ICP-OES and the Cu concentrations ranged from 13 to 45% m m−1. Partial least squares (PLS) regression was used to data fusion of analytical information from LIBS and micro-XRF analysis. The proposed calibration methods for LIBS and micro-XRF were tested for the 40 PCB subsamples, in which the best results were obtained combining both data sources though a low-level data fusion. Root mean square error of cross validation (RMSEC) and recoveries were 3.23% m m−1 and 81–119% using leave-one-out cross validation.

СПОСОБИ МЕТАЛІЗАЦІЇ КЕРАМІКИ, ВИКОРИСТОВУВАНІ ПРИ ВИРОБНИЦТВІ СИЛОВИХ ЕЛЕКТРОННИХ МОДУЛІВ І ЕЛЕКТРОВАКУУМНИХ ПРИЛАДІВ

Power electronic modules are used in engineering related to the need to transmit high-current signals. Typical areas of application of such modules are aircraft navigation systems, elements of switching power circuits and other high-load connections. The central unit of the module is a ceramic base, on which conductive tracks are formed and electronic components are mounted. The finished substrate is often called a switchboard. The substrate performs two main functions: Is the dielectric basis of the printed circuit formed on one or two sides. Provides heat dissipation emitted by semiconductor crystals and circuit elements. Used for substrates non-hygroscopic ceramics, heat-resistant, is an insulating material with high mechanical and dielectric properties. It is relatively easy to manufacture and low cost. In the manufacture of power modules using ceramic substrates of aluminum oxide or nitride with a multilayer metallized coating with a thickness of several microns to several tens of microns (depending on the application), which provides the required degree of adhesion of the coating to ceramics and applied on one or both sides. The main requirements for the finished product are the minimum dimensions and low cost of materials and production process. In addition, the decisive factors are high technical characteristics, resistance to environmental influences and reliability. The design of the finished module must provide minimum values of transient thermal resistances, distributed inductances of power busbars, high insulation voltage. Adhesion strength depends on many factors: coating technology, film material, substrate material; and may decrease during operation of the finished product. During the operation of power modules, they are subjected to thermal and mechanical loads, including vibration. This leads to the destruction of components from overheating and damage to the mechanical damage of the modules. Often the failure occurs in the structure of the substrate-coating conductor. The main reason for this destruction is the low adhesive strength of the metal film to the ceramic base.

Development of a full roll-to-roll manufacturing process of through-substrate vias with stretchable substrates enabling double-sided wearable electronics

In the recent years, there has been a growing interest towards printed stretchable electronics used in diagnostics, health-monitoring, and wearable applications. Double-sided electronic circuits with through-substrate vias offer a solution where the amount of printed circuitry and assembled SMDs (surface-mount devices) in direct contact with the human skin can be minimized. This improves not only the wearability and cost-effectiveness of the printed electronic devices but also the product safety and comfort to wear. Another factor decreasing the unit costs in printed electronics is the use of high volume, high speed, and continuous roll-to-roll (R2R) manufacturing processes. In this current paper, a full R2R process for the manufacturing of through-substrate vias on stretchable thermoplastic polyurethane (TPU) substrate was developed and verified. The through-substrate via-holes were manufactured in R2R using either laser-cutting or die-cutting. Rotary screen printing was used to print conductive tracks onto both sides of the stretchable substrate and to fill the via-holes. Eventually, conductive and stretchable through-substrate vias with low sheet resistance and low resistance deviation were reliably achieved with the developed process.

Material ejection dynamics in direct-writing of low resistivity tracks by laser-induced reverse transfer

Laser-induced reverse transfer (LIRT) is a direct-write technique for patterning materials onto transparent substrates. A laser pulse transmits through the transparent material and a small air gap to ablate a donor target surface, the vaporised target species then transfer to the transparent material. There is not yet a detailed understanding of the material ejection and deposition processes, and reports show high-resistivity films and only limited demonstration of conductive linear tracks. Here we use a recently developed capability of holographic phase contrast imaging at nanosecond temporal resolution to report the morphology of the confined ablation plume. This reveals previously unobserved phenomena such as the influence of the rebounding pressure wave and a >80% longer plasma lifetime of a confined plume, showing the importance of plume shielding and incubation effects for applications. Focusing on silver, graphite and copper, static and scanned beam experiments show the dominant role of sputtering of fragmented particles rather than vapour condensation. The results highlight the challenges in using LIRT for conformal coating without surface damage but will excite further study of this rarely explored technique, with potential for facile, reliable fabrication of conductive patterns and digitally controlled customisation of glass products for applications such as embedded sensors and electronics.

Evaluating thermoset resin substrates for 3D mechatronic integrated devices and packaging

AbstractMiniaturization efforts and increasing demands regarding reliability of mechatronic systems require new materials and processes for the 3D mechatronic integrated devices (3D-MID) technology. Currently, in the area of 3D-MID mostly thermoplastic materials are in use in the industry, which are metallized using the LPKF-LDS® process. This paper is supposed to demonstrate the eligibility of thermoset resins as a new material class for 3D-MID applications and as a packaging option for silicon chips which are currently encapsulated using transfer molding of thermosets. The reliability of the conductor tracks made using a LDS-additive free process as well as the adhesion forces are investigated. Different laser parameters for structuring of two different substrate materials are compared. For reliability testing a thermal shock test is applied. Furthermore, the adhesion is tested using Hot-Pin-Pull testing. The conductor tracks surpass 2000 cycles thermo-mechanical load without showing strong deterioration of the track resistivity. The incorporated approach enables electrically reliable functionalization of packaged dummy chips including vias for connection to terminals on the chips. The results of the tested injection moldable thermoset resins are comparable to state-of-the-art 3D-MID thermoplastic substrates and thus, suited as circuit carrier material in electronic packaging.

Scalable Process to Develop Durable Conductive Cotton Fabric

Developing a scalable process is critical to manufacture conductive fabric for commercial applications. This paper describes a scalable coating process that is compatible with existing industrial finishing processes of fabrics. In this process, the fabric is continuously dipped in water-based metal salt and the reducing agent solution to impart conductive particles on the fiber surface. After 10 consecutive cycles of dip coating, the fabric shows 6 Ω/in. of resistance. The process is tuned to minimize process cost and material cost, and maximize the durability of the fabric. This paper also introduces an easy protective coating technique of the conductive fabric that improves the durability of the conductive fabric without sacrificing the comfort properties of textile fabrics such as breathability and flexibility. The encapsulated conductive fabric shows good air-permeability and it is 6.96 cm3/cm2/s. Moreover, the conductivity of the encapsulated fabric is quite stable after four accelerated washing cycles. Additionally, the fabric remains conductive on the surfaces and is suitable for using as a conductive track and connectors.

A fully printed flexible multidirectional thermal flow sensor

This work presents the development and evaluation of a fully printed multi-directional thermal flow sensor on PET substrate. The device consists of conductive Ag tracks and printed thermistors based on BaTiO3, activated carbon and a solvent based thermoset polymeric system. Each element presents similar temperature—electrical resistance behavior (in terms of normalized values), thus enabling utilization as sensing and active elements for thermal two-dimensional flow sensing. A custom experimental setup was used for evaluating the device under two modes of operation, namely constant current and constant resistance. It was observed that in the range of 0 to 25 standard liters per second (SLPM) of air flow, constant resistance provided better input dynamic range than constant current (2.75 and 0.12 mW respectively), while constant resistance mode exhibited a sensitivity of approximately two orders of magnitude greater than that of constant current mode. For constant resistance mode, sensitivities of 0.46 mW/SLPM for zero flow and 0.08 mW/SLPM for flow greater than 6 SLPM were extracted, while for constant current mode the corresponding sensitivity values were 0.018 mW/SLPM for zero flow and 0.0036 mW/SLPM for flow greater than 6 SLPM. The device was capable of successfully detecting the flow direction throughout the target flow range. The influence of the flow magnitude on detecting flow angle was found to be negligible. The proposed device can be mounted to various non-planar surfaces, after the necessary re-calibration. It can be mass produced with various printing technologies for applications as a flexible two-dimensional flow sensor with low fabrication cost.

Optimal Design of Pneumatic Flotation for Roll-to-Roll Conveyance in the Production of Printed Circuits

Flexible printed electronic circuits have recently attracted attention as an alternative promising methodology due to the additive process being more environmentally friendly and using less raw material compared to conventional lithography and chemical vapor deposition. However, printed circuits produced by roll-to-roll (R2R) conveyance are often scratched, which can result in breaks in the conductive tracks, cracks, or pinholes. This study investigated a proposed optimal design for an air bar for use in an R2R printing system. The optimal distance between the roll surface and floating substrate for preventing scratching of the printed circuit was investigated. The optimal design—including the blower frequency, size of air holes, and density of air holes—was investigated using simulations of fluid–structure interactions for estimating substrate behavior during pneumatic flotation. The distribution of air pressure in the space between the substrate and the surface of the air bar was calculated, and the deformation of the substrate by the air pressure was analyzed. The optimal design of the air bar was verified in numerical simulations and experiments using various conditions.

Mechanically driven strategies to improve electromechanical behaviour of printed stretchable electronic systems

Stretchable electronics promise to extend the application range of conventional electronics by enabling them to keep their electrical functionalities under system deformation. Within this framework, development of printable silver-polymer composite inks is making possible to realize several of the expected applications for stretchable electronics, which range from seamless sensors for human body measurement (e.g. health patches) to conformable injection moulded structural electronics. However, small rigid electric components are often incorporated in these devices to ensure functionality. Under mechanical loading, these rigid elements cause strain concentrations and a general deterioration of the system’s electrical performance. This work focuses on different strategies to improve electromechanical performance by investigating the deformation behaviour of soft electronic systems comprising rigid devices through Finite Element analyses. Based on the deformation behaviour of a simple stretchable device under tensile loading, three general strategies were proposed: local component encapsulation, direct component shielding, and strain dispersion. The FE behaviour achieved using these strategies was then compared with the experimental results obtained for each design, highlighting the reasons for their different resistance build-up. Furthermore, crack formation in the conductive tracks was analysed under loading to highlight its link with the evolution of the system electrical performance.

Performance evaluation of conductive tracks in fabricating e-textiles by lock-stitch embroidery

Lock-stitch embroidery has been the centre of much interest as a versatile and precise method of producing conductive tracks in the fabrication of wearable electronic devices. However, improper fabrication parameter settings could result in the nonconformity of the conductive tracks and damage the conductive coating of the conductive yarns. In this study, we evaluate the appearance quality, dimensional stability and electrical resistance of conductive tracks by taking into account the embroidering speed (ES), stitch length (SL), needle thread pre-tension (NTP) and embroidering direction (ED). The conductive tracks are embroidered onto knitted fabric in different directions with silver-coated polyamide yarn as the needle thread. The results show that stitching the conductive tracks in the wale direction results in a more uniform stitch lines in comparison to the other directions. To resolve the problem of floated stitches, it is recommended that an SL of 4 mm and a higher NTP are used. The percentage of shrinkage in the wale direction is lower than in the course direction. The electrical resistance of the conductive tracks increases with a higher ES and shorter SL. It is also found that a thicker yarn is more sensitive to the NTP and some of the silver coating is rubbed off with an NTP of 50 gf. We also carry out an overlay plot analysis, through which we predict and validate the optimal embroidery parameters that balance appearance quality and electrical resistance. The technique parameters in this study can be used to embroider conductive tracks for smart clothing.

Innovative processing route combining fused deposition modelling and laser writing for the manufacturing of multifunctional polyamide/carbon fiber composites

An innovative manufacturing method, based on Fused Deposition Modelling (FDM) and Laser Writing (LW) technologies, was developed to integrate electrically conductive tracks within high strength 3D printed parts. Carbon fibers reinforced polyamide composites were processed by FDM according to three different printing architectures by varying the raster angle in the layer sequence. Laser writing was then performed to obtain conductive tracks on the surface of the printed parts. The process-structure-property relationship of components before and after the writing of conductive tracks was investigated. The tensile behaviour and the track resistance of samples were correlated to the direction of filament extrusion within the layers, and consequently to fibers orientation. Tracks showing good aesthetic quality and the lowest electrical resistance were obtained on samples with [±45] architecture. These tracks displayed the lowest electrical resistance ever reached by laser writing on metal-free polymer composites (0.008 kΩ/cm). Samples with [±45] architecture also showed high strength (72.9 MPa) and stiffness (7.7 GPa). The integration of FDM and LW emerges as a new approach to transform the surface of high strength polymer composites parts into a highly valuable system. These multifunctional components can find applications in several industrial fields such as automotive, aeronautics, and appliances.

The Efficacy of Polymer Coatings for the Protection of Electroless Copper Plated Polyester Fabric.

The selective metallisation of textiles is becoming a very important process in the development of electronic or e-textiles. This study investigated the efficacy of polymer coatings for the protection of copper (Cu) conductive tracks electroless plated on polyester (PES) fabric against laundering and rubbing, without essentially affecting the physical-mechanical and optical properties of the base material. After the electroless deposition of a consistent layer of Cu onto PES, four polymers were applied individually by screen-printing or padding. The physical-mechanical characterisation of coated textiles revealed that polyurethane resin (PUR) and modified acrylate resin (AR) had little effect on the air permeability, tensile strength and breaking tenacity of the PES, as compared to silicone elastomer polydimethylsiloxane (PDMS) and epoxy resin (ER). On the other hand, PUR and PDMS had higher abrasion resistance and photo-stability under prolonged UV irradiation, as compared to AR and ER. In addition, freshly Cu plated samples were coated with polymers, washed up to 30 cycles and characterised by measuring their electrical resistivity, determination of colour changes and the examination of the surface morphology. Based on these results, PUR presented the most suitable protection of Cu tracks on PES, with the lowest impact on physical-mechanical properties. ER is not recommended to be used for protection of Cu tracks on fabrics, due to its rigidity, low photo-stability, washing and wear durability.

Woven Textile Pressure Switch

In this paper has shown that the three-dimensional hollow weaving technique enables to produce a textile pressure sensor in one continuous process. Based on the multilayer fabric principle, the hollow woven fabrics can be created by connecting adjacent layers of the fabrics according to certain rules. The appropriate fabric structure has been selected and the three-layer weaving technique was used to make the textile pressure switch. The fabric structure is selected to ensure that the top and bottom layers are kept at a distance from each other. The electrically conductive tracks were embedded in the hollow structure of the fabric in bottom and middle layers. Three conditions must be fulfilled in order to create the textile switch: a) the fabric in normal condition keeps the shape required, i.e. the conductive elements are physically separated from each other; b) when the fabric is pressed, conductive elements are in contact, i.e. the switch is now in an electrically on state; c) after the pressure has been removed the fabric returns to its original position, i.e. switch is in an electrically off state. The behavior of the electrically conductive yarn and conductive tracks were tested in various ways. The stainless steel yarn woven in particular way can be used to create woven conductive tracks. Example of application: the pressure sensitive woven rug, the whole area or part of which acts as the pressure sensor or simple switch. The pressure switch in the floor coverings can turn on alarm systems or indicator lamps in the floor or wall coverings for guidance systems in public buildings.

On the Feasibility of Fan-Out Wafer-Level Packaging of Capacitive Micromachined Ultrasound Transducers (CMUT) by Using Inkjet-Printed Redistribution Layers.

Fan-out wafer-level packaging (FOWLP) is an interesting platform for Microelectromechanical systems (MEMS) sensor packaging. Employing FOWLP for MEMS sensor packaging has some unique challenges, while some originate merely from the fabrication of redistribution layers (RDL). For instance, it is crucial to protect the delicate structures and fragile membranes during RDL formation. Thus, additive manufacturing (AM) for RDL formation seems to be an auspicious approach, as those challenges are conquered by principle. In this study, by exploiting the benefits of AM, RDLs for fan-out packaging of capacitive micromachined ultrasound transducers (CMUT) were realized via drop-on-demand inkjet printing technology. The long-term reliability of the printed tracks was assessed via temperature cycling tests. The effects of multilayering and implementation of an insulating ramp on the reliability of the conductive tracks were identified. Packaging-induced stresses on CMUT dies were further investigated via laser-Doppler vibrometry (LDV) measurements and the corresponding resonance frequency shift. Conclusively, the bottlenecks of the inkjet-printed RDLs for FOWLP were discussed in detail.

Liquid Crystal Elastomer Electric Locomotives.

In this letter, we present an electro-driven cylindrical actuator system composed of a bilayered liquid crystal elastomer/carbon black (LCE/CB) electro-driven soft actuator and a conductive track. The bilayered LCE/CB electro-driven actuator consists of an inner LCE circular band and several U-shaped CB conductive regions stuck on the outer surface of the LCE ring. Benefiting from the effective Joule heating of CB powder and the consequential inhomogeneous stress generated inside the bilayered LCE/CB film, the cylindrical actuator can roll forward with a rate of 1.6 mm/s along a stationary copper conductive track powered by a 50 V direct current supply. The dynamic connection between the rolling actuator and the conductive track effectively eliminates the limitation of electric wires in the complicated actuation set-ups of the LCE materials. This work might promote the development of electro-driven LCE actuators and have potential applications in the fields of soft robots and electric devices.

Effect of long-term mechanical cycling and laser surface treatment on piezoresistive properties of SEBS-CNTs composites

The piezoresistive behaviour of SEBS-CNTs nanocomposites was investigated to evaluate their.potential applications as strain sensors. Composites containing from 3%wt. to 7%wt. of CNTs were processed by injection moulding in order to evaluate the percolation threshold. The piezoresistive response under flexural strain of nanocomposites with a CNTs content above the percolation threshold was then studied. The nanocomposites showing the most promising performance were tested under cyclic conditions. Conductive tracks were then processed on nanocomposites surfaces (with 3 and 4% of CNTs) by means of a laser treatment. Samples with optimized laser tracks were then submitted to 1000 stretching/releasing cycles, showing improved piezoresistive performance.