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1 – 10 of over 4000Yansong Tan, Xin Li, Xu Chen, Zhenwen Yang and Guo-Quan Lu
This paper aims to use nano-silver paste to design a new bonding method for super-large-area direct-bonded-aluminum (DBA) plates. It compared several frequently used bonding…
Abstract
Purpose
This paper aims to use nano-silver paste to design a new bonding method for super-large-area direct-bonded-aluminum (DBA) plates. It compared several frequently used bonding methods and proved the feasibility of an optimized low-pressure-assisted double-layer-printed silver sintering technology for large-area bonding to increase the thermal conductivity of power electronic modules with high junction temperature, higher power density and higher reliability.
Design/methodology/approach
The bonding profile was optimized by using transparent glasses as substrates. Thus, the bonding qualities could be directly characterized by optical observation. After sintering, the bonded DBA samples were characterized by nondestructive X-ray computed tomography system, scanning electron microscopy equipped with an energy dispersive spectrometer. Finally, bonding stress evolution was characterized by shear tests.
Findings
Low-pressure-assisted large-area double-layer-printed bonding process consisting of six-step was successfully developed to bond DBA substrates with the size of 50.8 × 25.4 mm. The thickness of the sintered-silver bond-line was between 33 and 74 µm with the average porosity of 12.5 per cent. The distribution of shear strength along the length of DBA/DBA bonded sample was from 9.7 to 18.8 MPa, with average shear strength of 15.5 MPa. The typical fracture primarily propagated in the sintered-silver layer and partially along the Ni layer.
Research limitations/implications
The bonding stress needs to be further improved. Meanwhile, the thermal and electrical properties are encouraged to test further.
Practical implications
If nano-silver paste can be used as thermal interfacial material for super-large-area bonding, the thermal performance will be improved.
Social implications
The paper accelerated the use of nano-silver paste for super-large-area DBA bonding.
Originality/value
The proposed bonding method greatly decreased the bonding pressure.
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Keywords
Qiyin Lin, Zhengying Wei, Ning Wang and Wei Chen
The purpose of this paper is to study the influence of large-area texture/slip surface, especially the area and position of large-area texture surface on journal bearing, and…
Abstract
Purpose
The purpose of this paper is to study the influence of large-area texture/slip surface, especially the area and position of large-area texture surface on journal bearing, and improve the tribological performances of journal bearing.
Design/methodology/approach
A modified texture/slip numerical boundary condition with double parameters is presented and is applied onto the region where surface textures locate to represent the impact of actual texture/slip surface. A phase change condition is used to analyze cavitation phenomena.
Findings
The global/cumulative texture effect can be represented by applying texture/slip condition onto the region where it locates. The area and position of texture/slip surface would significantly affect the cavitation and load-carrying capacity. Texture/slip surface would not affect the pressure and load-carrying capacity when it locates at cavitation zone. The effect of texture/slip surface on load-carrying capacity would be beneficial if it locates at the pressure rise region, but its effect would be adverse if it locates at the pressure drop region. Well-designed texture/slip surface can improve tribological performances.
Originality/value
The developed texture/slip boundary condition can be a suitable and useful tool to analyze the effect of large-area texture/slip surface and especially to optimize the area and position of large-area texture surface. This approach can be complementary to conventional approach which is used to analyze the influence of textures’ real configurations and parameters.
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Riyaz Ali Shaik and Elizabeth Rufus
This paper aims to review the shape sensing techniques using large area flexible electronics (LAFE). Shape perception of humanoid robots using tactile data is mainly focused.
Abstract
Purpose
This paper aims to review the shape sensing techniques using large area flexible electronics (LAFE). Shape perception of humanoid robots using tactile data is mainly focused.
Design/methodology/approach
Research papers on different shape sensing methodologies of objects with large area, published in the past 15 years, are reviewed with emphasis on contact-based shape sensors. Fiber optics based shape sensing methodology is discussed for comparison purpose.
Findings
LAFE-based shape sensors of humanoid robots incorporating advanced computational data handling techniques such as neural networks and machine learning (ML) algorithms are observed to give results with best resolution in 3D shape reconstruction.
Research limitations/implications
The literature review is limited to shape sensing application either two- or three-dimensional (3D) LAFE. Optical shape sensing is briefly discussed which is widely used for small area. Optical scanners provide the best 3D shape reconstruction in the noncontact-based shape sensing; here this paper focuses only on contact-based shape sensing.
Practical implications
Contact-based shape sensing using polymer nanocomposites is a very economical solution as compared to optical 3D scanners. Although optical 3D scanners can provide a high resolution and fast scan of the 3D shape of the object, they require line of sight and complex image reconstruction algorithms. Using LAFE larger objects can be scanned with ML and basic electronic circuitory, which reduces the price hugely.
Social implications
LAFE can be used as a wearable sensor to monitor critical biological parameters. They can be used to detect shape of large body parts and aid in designing prosthetic devices. Tactile sensing in humanoid robots is accomplished by electronic skin of the robot which is a prime example of human–machine interface at workplace.
Originality/value
This paper reviews a unique feature of LAFE in shape sensing of large area objects. It provides insights from mechanical, electrical, hardware and software perspective in the sensor design. The most suitable approach for large object shape sensing using LAFE is also suggested.
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Lifang Wu, Lidong Zhao, Meng Jian, Yuxin Mao, Miao Yu and Xiaohua Guo
In some three-dimensional (3D) printing application scenarios, e.g., model manufacture, it is necessary to print large-sized objects. However, it is impossible to implement…
Abstract
Purpose
In some three-dimensional (3D) printing application scenarios, e.g., model manufacture, it is necessary to print large-sized objects. However, it is impossible to implement large-size 3D printing using a single projector in digital light processing (DLP)-based mask projection 3D printing because of the limitations of the digital micromirror device chips.
Design/methodology/approach
A multi-projector DLP with energy homogenization (EHMP-DLP) scheme is proposed for large-size 3D printing. First, a large-area printing plane is established by tiling multiple projectors. Second, the projector set’s tiling pattern is obtained automatically, and the maximum printable plane is determined. Third, the energy is homogenized across the entire printable plane by adjusting gray levels of the images input into the projectors. Finally, slices are automatically segmented based on the tiling pattern of the projector set, and the gray levels of these slices are reassigned based on the images of the corresponding projectors.
Findings
Large-area high-intensity projection for mask projection 3D printing can be performed by tiling multiple DLP projectors. The tiled projector output energies can be homogenized by adjusting the images of the projectors. Uniform ultraviolet energy is important for high-quality printing.
Practical implications
A prototype device is constructed using two projectors. The printable area becomes 140 × 210 mm from the original 140 × 110 mm.
Originality/value
The proposed EHMP-DLP scheme enables 3D printing of large-size objects with linearly increasing printing times and high printing precision. A device was established using two projectors to practice the scheme and can easily be extended to larger sizes by using more projectors.
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Justin Nussbaum and Nathan B. Crane
Projection sintering, a system for selectively sintering large areas of polymer powder simultaneously with a high-power projector is introduced. This paper aims to evaluate the…
Abstract
Purpose
Projection sintering, a system for selectively sintering large areas of polymer powder simultaneously with a high-power projector is introduced. This paper aims to evaluate the suitability of laser sintering (LS) process parameters for projection sintering, as it uses substantially lower intensities, longer exposure times and larger areas than conventional LS.
Design/methodology/approach
The tradeoffs in sintering outcomes are evaluated by creating single layer components with varied exposure times and optical intensities. Some of these components were cross-sectioned and evaluated for degree of densification, while the single-layer thickness and the maximum tensile force was measured for the rest.
Findings
Shorter exposure times and higher intensities can create thicker and therefore stronger parts than when equal energy is applied over longer exposures. This is different from LS in which energy input (Andrew’s Number) is accepted as a reliable process variable. This difference is likely because significant thermal energy is lost from the sintering region during the exposure time – resulting in reduced peak temperatures. These thermal losses can be offset by imparting additional energy through increased exposure time or light intensity.
Practical implications
Most methods for evaluating LS process parameters, such as the energy melt ratio and Andrew’s Number, estimate energy input from basic process parameters. These methods do not account for thermal losses and assume that the powder absorbs all incident light. These methods become increasingly inaccurate for projection sintering with visible light where exposure times are much higher (>1s) and a larger portion of the light is reflected from the power’s surface. Understanding the appropriate sintering criteria is critical for the development of long-exposure sintering.
Originality/value
A new method of selectively sintering large areas is introduced that could sinter a wider variety of materials by enabling longer sintering times and may increase productivity relative to LS. This work shows that new processing parameters are required for projection sintering as traditional LS process parameters are inadequate.
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Grzegorz Wroblewski, Konrad Kielbasinski, Barbara Swatowska, Janusz Jaglarz, Konstanty Marszalek, Tomasz Stapinski and Malgorzata Jakubowska
The paper aims to present the research results related to transparent heating elements made from carbon nanomaterials. Heating elements were fabricated only with cost-effective…
Abstract
Purpose
The paper aims to present the research results related to transparent heating elements made from carbon nanomaterials. Heating elements were fabricated only with cost-effective techniques with the aim to be easily implemented in large area applications. Presented materials and methods are an interesting alternative to vacuum deposition of transparent resistive layers and etching of low-resistive patterns. Fabricated heating elements were designed to be used as de-icing structures in roof-top windows.
Design/methodology/approach
The paper presents the research results related to transparent heating elements made from carbon nanomaterials. Heating elements were fabricated only with cost-effective techniques with the aim to be easily implemented in large area applications. Presented materials and methods are an interesting alternative to vacuum deposition of transparent resistive layers and etching of low-resistive patterns. Fabricated heating elements were designed to be used as de-icing structures in roof-top windows.
Findings
The sheet resistance of obtained layers was between 9 and 11 kΩ/□; however, double-walled carbon nanotubes showed significantly higher optical transmission (around 70 per cent) than graphene nanoplatelets (around 55 per cent for visible and near infrared range). The amount of polymer resin had the influence on the paints stability, electrical properties and coatings adhesion.
Originality/value
Results show a novel method of fabrication of a large area and transparent heating elements with tunable resistance done through the change of spray coating paint composition.
Details
Keywords
Mingang Gao, Hong Chi, Baoguang Xu and Ruo Ding
The purpose of this paper is to focus on disruption management responding to large‐area flight delays (LFD). It is urgent for airways to reschedule the disrupted flights so as to…
Abstract
Purpose
The purpose of this paper is to focus on disruption management responding to large‐area flight delays (LFD). It is urgent for airways to reschedule the disrupted flights so as to relieve the negative influence and minimize losses. The authors try to reduce the risk of airline company's credit and economic losses by rescheduling flights with mathematic models and algorithm.
Design/methodology/approach
Based on flight classifications of real‐time statuses and priority indicators, all flights are prioritized. In this paper, two mathematic programming models of flight rescheduling are proposed. For the second model, an optimum polynomial algorithm is designed.
Findings
In practice, when LFD happens, it is very important for the airline company to pay attention to real‐time statuses of all the flights. At the same time, the disruption management should consider not only the economic loss but also other non‐quantitative loss such as passengers' satisfaction, etc.
Originality/value
In this paper, two mathematic programming models of flight rescheduling are built. An algorithm is designed and it is proved to be an optimum polynomial algorithm and a case study is given to illustrate the algorithm. The paper provides a theory support for airways to reduce the risk brought by LFD.
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Keywords
Rabindra N. Das, How T. Lin, John M. Lauffer and Voya R. Markovich
There has been increasing interest in the development of printable electronics to meet the growing demand for low‐cost, large‐area, miniaturized, flexible and lightweight devices…
Abstract
Purpose
There has been increasing interest in the development of printable electronics to meet the growing demand for low‐cost, large‐area, miniaturized, flexible and lightweight devices. The purpose of this paper is to discuss the electronic applications of novel printable materials.
Design/methodology/approach
The paper addresses the utilization of polymer nanocomposites as it relates to printable and flexible technology for electronic packaging. Printable technology such as screen‐printing, ink‐jet printing, and microcontact printing provides a fully additive, non‐contacting deposition method that is suitable for flexible production.
Findings
A variety of printable nanomaterials for electronic packaging have been developed. This includes nanocapacitors and resistors as embedded passives, nanolaser materials, optical materials, etc. Materials can provide high‐capacitance densities, ranging from 5 to 25 nF/in2, depending on composition, particle size, and film thickness. The electrical properties of capacitors fabricated from BaTiO3‐epoxy nanocomposites showed a stable dielectric constant and low loss over a frequency range from 1 to 1,000 MHz. A variety of printable discrete resistors with different sheet resistances, ranging from ohm to Mohm, processed on large panels (19.5×24 inches) have been fabricated. Low‐resistivity materials, with volume resistivity in the range of 10−4‐10−6 ohm cm, depending on composition, particle size, and loading, can be used as conductive joints for high‐frequency and high‐density interconnect applications. Thermosetting polymers modified with ceramics or organics can produce low k and lower loss dielectrics. Reliability of the materials was ascertained by (Infrared; IR‐reflow), thermal cycling, pressure cooker test (PCT) and solder shock testing. The change in capacitance after 3× IR‐reflow and after 1,000 cycles of deep thermal cycling between −55°C and +125°C was within 5 per cent. Most of the materials in the test vehicle were stable after IR‐reflow, PCT, and solder shock.
Research limitations/implications
The electronic applications of printable, high‐performance nanocomposite materials such as adhesives (both conductive and non‐conductive), interlayer dielectrics (low‐k, low‐loss dielectrics), embedded passives (capacitors and resistors), and circuits, etc.. are discussed. Also addressed are investigations of printable optically/magnetically active nanocomposite and polymeric materials for fabrication of devices such as inductors, embedded lasers, and optical interconnects.
Originality/value
A thin film printable technology was developed to manufacture large‐area microelectronics with embedded passives, Z‐interconnects and optical waveguides, etc. The overall approach lends itself to package miniaturization because multiple materials and devices can be printed in the same layer to increase functionality.
Details
Keywords
Francis J. Dance and John L. Wallace
For a full realisation of the packaging advantages of leadless ceramic chip carriers, these devices will be surface mounted on large area printed circuit boards. However, thermal…
Abstract
For a full realisation of the packaging advantages of leadless ceramic chip carriers, these devices will be surface mounted on large area printed circuit boards. However, thermal management and solder joint reliability concerns preclude the usage of conventional board materials and manufacturing processes in most high reliability applications. A new approach for achieving rugged, large area PCBs, incorporating thermal planes and the necessary thermal expansion match to chip carriers is described in this paper. The approach is based upon the use of a clad metal core substrate material fabricated from high conductivity copper and low thermal expansion rate Invar TM, a 36% nickel‐64% iron alloy. Mechanical, electrical and thermal properties of this clad metal are presented as well as techniques for adaption of PCB and porcelain/thick film technologies. Finally, other potential applications for this clad metal in the electronics industry are discussed.
S. Fuchs, K. Rindelhardt, J. Barrett and F. Stam
Describes the modification of a laboratory flip‐chip bonder to allow bonding of very large chips. The original optical system of the bonder was designed for chip sizes up to 5.0 …
Abstract
Describes the modification of a laboratory flip‐chip bonder to allow bonding of very large chips. The original optical system of the bonder was designed for chip sizes up to 5.0 ¥ 5.0mm2. It was desired to use the system for bonding chips larger than this, up to 23.0 ¥ 23.0mm2. Therefore a modification of the existing system was needed. Several options for purely optical modifications were identified and investigated. It was concluded that all optical solutions considered were not feasible because of either size or cost. Therefore attention was directed to a “mechanical solution”. The system was modified using a guide‐rail to move the microscope along the chip diagonally. It was proven that this works reliably for any size of chip. The overall costs of this solution are relatively low. It can be easily implemented for this type of bonder, which is widely used in laboratory flip‐chip research.