A position measurement system for precision alignment of roll-to-roll printing and sensitivity analysis of thermal deformation

Roll-to-roll processing in the field of printed electronics is the process of creating electronic circuits or devices on a roll of flexible plastic or metal foil, and it can be used in the manufacture of many products, such as RFID tags, solar cells, and flexible display panels, at a much lower cost than that in the semiconductor lithography process. This process is also more efficient in producing electronic devices in a large volume than semiconductor lithography. As with lithography, roll-to-roll processing also needs to achieve accurate layer-to-layer alignment in fabricating multi-layered circuits or devices. This alignment precision, in fact, is a critical factor in determining the integration and performance of printed electronics. In other words, it is essential to achieve highly precise alignment in roll-to-roll printing for the full commercialization of printed electronics. To that end, this study proposes an alignment pattern that is directly printed on a web as a solution that can enhance the alignment precision in roll-to-roll printing. Based on this, the study also proposes a web position measurement system using optical measurement instruments and verifies its applicability and reliability. Considering the fact that tension on the web and heat generated in the process of curing may deform the web, we conducted experiments and simulations to analyze the measurement sensitivity when the web is actually deformed and we present the results of the study.     

A novel cross directional register modeling and feedforward control in multi-layer roll-to-roll printing

For the adaption of roll-to-roll printing method to the printed electronics, it is mandatory to increase the resolution of register control. Therefore, it is desired to derive a mathematical model for register and to develop a controller to reduce the register error. The cross direction register error was derived considering both the lateral motion of a moving web and the transverse position of a printing roll. And a feedforward control method was proposed to cancel out the disturbance of CD register from upstream span. The proposed controller could be used to improve the performance of the CD register controller in a large area roll-to-roll printing machine. The mathematical modeling and proposed control method were validated by numerical simulations and experimental verifications in various operating conditions using a multi-layer direct gravure printing machine. These results show that the proposed feedforward control scheme greatly improves the control performance of register control in overcoming the upstream disturbances.     

Preview control of web position in roll-to-roll printing using alignment patterns

In printed electronics systems, the roll-to-roll process is a next-generation process technology that may be applied to the production of various electronic products such as flexible electronic devices, solar cells, and display panels. The process allows for production at low unit cost and high speed. As a factor for improving the print quality, there are ink viscosity, printing speed, printing pressure, and alignment precision. Among these factors, alignment precision, a critical factor in the performance of an electronic circuit, is the accurate alignment of layers in a multi-layered structure. In our previous study, we suggested a measurement method for improving the alignment precision by using an optical pre-measuring device and an alignment pattern that is printed by roll-to-roll printing process. In the measuring system, when a web is transported in the web feed direction, the optical pre-measuring device measures the quantity of light reflected by the alignment pattern. A lateral position can be aligned accurately based on the measured signal. However, because the position is measured in advance in the web feed direction, it is not applicable to a real-time printing system, and when the lateral position is measured using the optical pre-measuring device, a lateral position error, that is generated by disturbances induced by tension acting on the web and the vibration of the motor, can be estimated. A motor driven linear translation stage for lateral direction is used to minimize the lateral position errors in roll-to-roll systems. In this paper, we propose a preview control system to reflect the measured lateral position error to the printing result at the appropriate time for improving the alignment precision in roll-to-roll printing. As a control method, using roll-to-roll model, the system of disturbance, lateral angle and lateral position can be expressed as a state-space equation. Based on this equation, a preview controller to find the optimal value of state and control error is designed in a similar method to the conventional preview control method used for the active suspension system of a vehicle. Then, the alignment results are verified using another optical measuring device of a web transport system.

     

Analysis of dynamic thermal characteristic of register of roll-to-roll multi-layer printing systems

Register control is essential in the roll-to-roll printing of organic thin-film transistors. Specifically, microscale accuracy is required in the control of the overlay printing register. To achieve such precise control, the characteristics of the substrate under the operating conditions, such as the drying temperature and the tension applied to the substrate, should be considered. In this study, the variations of the elastic modulus and thermal deformation with the drying temperature were investigated, and the correlations among the change in the thermal characteristic of the substrate, the tension, and register error were also analyzed. The results of the analyses showed that the thermal deformation produced by the temperature change generated tension and register error, with the effect increasing with increasing drying temperature. System identification techniques were further used to develop a register model for estimating the register error due to thermal and elastic strains. The maximum estimation ability of 86.27% of the developed model is higher than that of a conventional register model.     

Modeling and compensation of the machine directional register in roll-to-roll printing

For mass manufacturing of printed electronics using roll-to-roll printing, high-resolution register control among multi-layers is required. A mathematical model of a machine directional (MD) register was derived, where the compensation method was proposed to cancel out the upstream disturbance of the MD register. The proposed MD register model and compensator could be used to improve the performance of the MD register controller in multi-layer roll-to-roll printed electronics. The proposed compensator was experimentally verified at various operating conditions. The results show that the proposed compensator improves the control performance of the MD register in overcoming upstream disturbances     

Statistical analysis on the effect of calendering process parameters on the geometry and conductivity of printed patterns

The quality of printed electronics products depends largely on geometrical and morphological characteristics of printed pattern, such as pattern thickness and surface roughness. In this study, we employ the calendering process in order to control the pattern thickness, surface roughness, and conductivity of printed pattern. Both pressure and heat are used to change micro structure as well as morphology of printed layer during the calendering process. The effect of process parameters including temperature, pressure, and speed are investigated by using statistical techniques. Individual effects and interaction effects of the parameters are analyzed with Analysis of Variance (ANOVA) method. The results show that the pattern thickness, surface roughness, and resistivity of printed pattern decrease with increase of temperature and pressure. We also report that temperature is the most influential factor among the parameters. This study demonstrates that the calendering process can be used to enhance the quality of printed electronics products by controlling the surface quality of printed layer.     

Microstructure Control in 3D Printing with Digital Light Processing

Digital light processing stereolithography is a promising technique for 3D printing. However, it offers little control over the surface appearance of the printed object. The printing process is typically layered, which leads to aliasing artefacts that affect surface appearance. An antialiasing option is to use greyscale pixel values in the layer images that we supply to the printer. This enables a kind of subvoxel growth control. We explore this concept and use it for editing surface microstructure. In other words, we modify the surface appearance of a printed object by applying a greyscale pattern to the surface voxels before sending the cross-sectional layer images to the printer. We find that a smooth noise function is an excellent tool for varying surface roughness and for breaking the regularities that lead to aliasing. Conversely, we also present examples that introduce regularities to produce controlled anisotropic surface appearance. Our hope is that subvoxel growth control in stereolithography can lead 3D printing towards customizable surface appearance. The printing process adds what we call ground noise to the printed result. We suggest a way of modelling this ground noise to provide users with a tool for estimating a printer's ability to control surface reflectance.     

Effect and experiment of curvature radius of 3‐D printed conformal load‐bearing antenna array on EM performance

Prototypes of a special conformal load‐bearing antenna array (CLAA) which has nondevelopable surface, are designed, fabricated, and tested, and the effect of the substrate curvature radius on its EM performance is also researched in this work. A novel three‐dimensional (3‐D) printing technology and fabrication equipment based on micro‐droplet spraying and metal laser sintering are proposed to create patch array and divider network on a non‐developable curved rigid substrate. In order to compare with conventional technology (such as chemical etching), a planar CLAA prototype with two patches, operating frequency at 5GHz, is designed and fabricated by two different technologies, the surface roughness, fabrication tolerance, and EM performance are tested and compared. Finally, a spherical CLAA prototype with eight patches, operating frequency at 13GHz, is designed and fabricated by the novel 3D printing, measured EM performance demonstrate the applicability of additive manufacturing for this special CLAA.     

Metal deposition on flexible membrane through the combination of localized electrochemical deposition and electroless plating

In this paper, we combined localized electrochemical deposition and electroless plating process for fabricating the metal pattern with the large area on flexible membrane. The pattern of the anode plate can rapidly transfer to the cathode membrane by localized electrochemical deposition. The thickness of the pattern can be increased by electroless plating process. The width of the mask pattern was close to the width of the final pattern. The anode plate can be used over fifty times for this process until the pattern was electrolyzed completely. This method provides a possible low cost approach to fabricate high metal structures on the flexible substrate with large area. It may have the potential to be applied in the fabrication of e-paper, flexible printed circuit and eventually adapted to roll-to-roll process.     

熔融沉积制造表面粗糙度参数显著性及预测模型研究

为了确定影响熔融沉积制造(FDM)打印件表面粗糙度的显著性因素,设计了基于 温度、打印速度和层厚的9 组正交实验。通过探针式粗糙度仪测量打印件表面粗糙度,并进行 了信噪比计算和波动分析,确定了影响表面粗糙度的显著性因素。利用田口法、多元回归方程 和指数方程对表面粗糙度进行预测,确定FDM 打印件最小表面粗糙度的参数组合。分析结果 表明：层厚对于表面粗糙度的影响程度最大,温度次之,打印速度最小;为了验证其有效性和 适用性,针对不同打印模型和FDM 打印机进行了验证性实验。实验结果表明：在预测模型方 面,多元回归方程的预测结果优于指数方程和田口法。并且,上述结论对不同打印模型和FDM 打印机具有较为宽泛的适用性。     

Large-area,high-temperature stainless steel foil substrate for manufacturing low-cost and flexible CMOS polysilicon TFTs

A large-area stainless steel foil substrate which is compatible with high-temperature (>800°C) processing was developed to support a hybrid printed and conventional process technology to fabricate polysilicon thin-film transistors (TFTs). The purpose was to build a platform that could lead to low-cost, roll-to-roll manufacturing of polysilicon TFTs. To fabricate a self-aligned top-gate TFT structure, a screen-printed dopant process, which requires high-temperature activation, was developed to substitute capital-intensive ion implantation. For the pilot line process, a 300-mm² and 100-μm-thick stainless steel substrate made of an alloy with a low thermal expansion coefficient (CTE) was chosen. Then, the foil finishing process was optimized to achieve flatness and minimize surface roughness. A barrier and dielectric encapsulation were developed to prevent trace metal diffusion from the substrate into the active layers. The polysilicon TFTs were then evaluated with static and dynamic bending tests.     

Super‐high‐resolution transfer printing for full‐color OLED display patterning

Abstract— A transfer‐printing method for the patterning of thin polymer layers is described. A hard stamp with a raised feature is brought into contact with a spin‐coated organic film under elevated pressure and temperature to break the films. The patterned film is then transfer printed onto the devices. This method is used to print red/green/blue subpixel arrays with a pattern size as small as 12 μm at a resolution of 530 ppi to demonstrate its ability for full‐color organic light‐emitting‐display fabrication. Devices with printed organic layers have similar performance to spin‐coated controls under optimized printing temperature and pressure settings. The critical physical parameters include a soft intermediate plate for the sharp breaking of edge patterns, control of surface energies, and printing at moderate temperature and pressure to achieve intimate contact between the printed layer and the underlying substrate.     

Roll‐to‐roll manufacturing considerations for flexible,cholesteric liquid‐crystal display (Ch‐LCD) media

Abstract— Roll‐to‐roll methods and equipment to manufacture a bistable, passively driven display media on a flexible substrate have been developed. Using continuous coating techniques and equipment, cholesteric liquid‐crystal droplets in a gelatin binder and a dark layer are simultaneously coated onto laser‐etched‐patterned transparent ITO conductors on a polymeric web. Second conductors are printed with a UV‐curable polymer thick‐film ink over the active display layers, followed by slitting and chopping to complete the manufacture of display media in a full roll‐to‐roll mode. Segmented‐ and matrix‐display media can be generated using these techniques. This paper will focus on the manufacturing considerations for producing matrix‐display media.     

Study of the hinge thickness deviation for a 316L parallelogram flexure mechanism fabricated via selective laser melting

3D printing offers great potential for developing complex flexure mechanisms. Recently, thickness-correction factors (TCFs) were introduced to correct the thickness and stiffness deviations of powder-based metal 3D printed flexure hinges during design and analysis. However, the reasons for the different TCFs obtained in each study are not clear, resulting in a limited value of these TCFs for future design and fabrication. Herein, the influence of the porous layer of 3D printed flexure hinges on the hinge thickness is investigated. Samples of parallelogram flexure mechanisms (PFMs) were 3D printed using selective laser melting (SLM) and 316L stainless steel powder. A 3D manufacturing error analysis was completed for each PFM sample via 3D scanning, surface roughness measurement and morphological observation. The thickness of the porous layer of the flexure hinge was independent of the designed hinge thickness and remained close to the average powder particle diameter. The effective hinge thickness could be estimated by subtracting twice the value of the porous layer thickness from the designed value. Guidelines based on finite element analysis and stiffness experiments are proposed. The limitations of the presented method for evaluating the effective hinge thickness of flexure hinges 3D printed via SLM are also discussed.

     

Three‐dimensional printing technologies for terahertz applications: A review

Three‐dimensional (3D) printing technologies enables fast prototyping of complex 3D objects with ever improving printing qualities. To date, 3D printing has been found useful in areas such as manufacturing, industrial design, aerospace, dental and medical industries, and many others. In this article, we review recent advances of 3D printing technologies for terahertz (THz) applications. Different 3D printing technologies and printable materials are first discussed and compared. 3D‐printed THz components and devices, which are categorized as waveguides/fibers, antennas, and quasi‐optical components, are further demonstrated. It is found that the performances and functionalities of 3D‐printed THz devices have been greatly enhanced, while the operating frequencies have been increased from the lower end of THz range to over 1 THz region. With further development of novel materials and printing techniques, it is believed that 3D printing technologies will play an important role in the realization of THz components for efficient control and manipulation of THz waves.     

Automated quality control of printed flasks and bottles

The paper faces the quality control problem for printed flasks, bottles and cans, used as containers for drugs and beverages. The control is mainly aimed at identifying ink spots and faded prints produced by a serigraphic process, but the approach is generically applicable to any kind of printing and printed cylindrical surface. Differently from the existing systems, based on the acquisition of good printed samples, the automatic control is based on the original digital image feeded to the printing system. Therefore, the control takes place directly between the ideal model and the result of a complex printing process including a number of distortion and noise sources. Problems related to image acquisition, reconstruction and alignment are investigated; a novel technique for image-model verification, based on adaptive local deformation, is also proposed and tested over a significant set of samples. A complete prototype system designed for such quality control is finally described and its operating capability on the field is discussed.     

Robust control of multistage printing systems

Printing errors (e.g. doubling) in multistage printing machines are mainly caused by web tension fluctuations, which arise from excessive rotation non-synchronization errors among the driven rollers in different stages (units). Therefore, the critical task in printing quality control is to attenuate web tension variations. In this paper, a robust H_∞ control strategy is proposed to attenuate tension fluctuations when the system is subject to disturbances and variations in speed or other operating conditions. Three system robustness properties are analyzed by using structured singular value analysis (μ-analysis). A systematic investigation is taken to analyze the impacts of different parameter variations on system robustness, with a purpose of providing a reference for achieving robust stability in a multistage printing system. The effectiveness of the proposed robust H_∞ controller is evaluated by both simulation and experimental tests.     

The FEM based liquid transfer model in gravure offset printing using phase field method

The velocity control of a roller is crucial in gravure offset printing for determining the quality of the printed images such as width and thickness of an electric circuit. The velocity control also affects mass printability, especially when using micro-scale liquid of high conductivity ink. In this work, a liquid transfer model for gravure offset printing is developed using the phase field method to investigate interfacial dynamics. As a numerical scheme, the finite element method is used for discretization of the partial differential equation. The interfacial layer governed by the phase field variable is embodied by the Cahn–Hilliard equation for a convection–diffusion problem. The numerical results are compared with those from the literatures for their validation. The results were found to be in good agreement with both analytical and experimental results in the literatures. After the validation, the effects of several key factors in gravure offset printing, such as velocity, gravity, surface tension and viscosity on liquid transfer are studied with respect to the contact angle of the upper plate. The ranges of the velocity and contact angle are varied from 0.01 to 0.25?m/s and from 30° to 70°, respectively. Also, the values of the surface tension and viscosity are changed from 0.5 to 1.5?N/m and from 0.05 to 0.15 N?s/m², respectively. The simulation result showed that at α?=?β?=?60° regardless of gravity, the liquid transfer rate (R _%) is increased as the velocity of the upper plate is increased at velocities below 0.01?m/s for liquid with low density, whereas the liquid transfer rate is decreased as the velocity is increased for liquid with high density. Also, the liquid transfer rate is increased as the surface tension is increased until the contact angle (α?≤?β?=?60°) approached 60°. Whereas the liquid transfer rate is decreased as the surface tension is increased until the contact angle (α?≤?β?=?60°) is increased to 60°.     

Fast patterning microstructures using inkjet printing conformal masks

The presented paper describes a novel process using inkjet printing to pattern a conformal (built-on) mask onto photoresist for further microstructure formation. The advantages of using the inkjet printing conformal mask include no Cr photomask required, suitable for non-planar substrate, scalable for large area, and extreme low cost. The ink is ejected from the inkjet print-head controlled by the inkjet system. A CAD pattern from the designer can use this process to place the pattern ink onto the photoresist substrate. A conformal mask (made of ink) was directly built-on the photoresist substrate. The dried ink thickness has to be more than 1.8 μm thick as UV absorber. Following UV exposure, development, and ink removal, the designed microstructure patterns can be realized in photoresist such as microchannels and micro-columns.     

Manufacture of microfluidic chips using a gap-control method based on traditional 3D printing technique

The solution to the commercialization of polymer microfluidic chips lies in the development of a low-cost and concise method. We present in this paper a gap-control method for obtaining low cost microfluidic chips on PMMA (polymethyl methacrylate) sheets based on traditional 3D printing technique—fused deposition modeling. The influence of 3D printing parameters such as printing temperature, printing speed, wire flow rate and initial layer thickness on printing quality is studied by experiments. The effect of O₂ plasma parameters such as chamber power and treatment time on the adhesion strength between printed PLA (polylactic acid) structures and PMMA substrate is investigated. The dye filling tests demonstrate that there is no blocking or leakage over the entire microchannels. With this newly developed technology, low-cost and large scale microfluidic chips can be fabricated, which allows commercial manufacturing of microchannels over large areas.