Special Issue "Selected Papers from the NMJ2018"

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Optics and Lasers".

Deadline for manuscript submissions: closed (31 December 2018)

Special Issue Editors

Guest Editor
Dr. Anming Hu

509 Dougherty Engineering Building, Department of Mechanical, Aerospace and Biomedical, University of Tennessee, Knoxville, TN, USA
Website | E-Mail
Phone: +1-865-974-5993
Fax: +1-865-974-5274
Interests: ultrafast laser materials interaction and processing; laser micro-nano manufacturing; laser 3D printing; nano-photonics; nanotechnology for electronics; sensing, energy and environmental applications
Guest Editor
Prof. Dr. Ing. Jolanta Janczak-Rusch

Überlandstrasse 129, Laboratory for Joining Technologies and Corrosion, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
Website | E-Mail
Phone: +41 58 765 4529
Interests: micro- and nano-joining; soldering; brazing and diffusion bonding; new joining materials and technologies; nano-multilayers; composite materials
Guest Editor
Prof. Dr. Tomokazu Sano

Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Japan
Website | E-Mail
Interests: laser nano-micro-macro-processing, laser nano/micro-joining, laser-matter interaction
Guest Editor
Dr. Peng Peng

Department of Materials Processing and Control Engineering, School of Mechanical Engineering and Automation, International Research Institute for Multidisciplinary Science, Beihang University, Beijing, 100191, China
Website | E-Mail
Phone: (+86)-130-5148-3485
Interests: micro/nano-joining and manufacturing, laser sintering, low temperature packaging for electronics, nanoengineering for water treatment

Special Issue Information

Dear Colleagues:

After the successful conferences in Niagara Falls, Canada in 2016 (NMJ2016), Emmetten, Switzerland in 2014 (NMJ2014) and Beijing, China in 2012 (NMJ2012), it is our pleasure to invite you to the 4th International Conference on Nanojoining and Microjoining (NMJ2018), which will be held in Nara, Japan on December 2–5, 2018. The conference provides a platform for scientific and industrial discussion and exchange in the emerging fields of nano and micro joining technologies, as follows:

  • Joining for integration of nano-/micro-scale materials and devices
  • Micro joining for assembly of implantable medical devices
  • Method development for nano/micro joint characterization
  • Mechanisms and materials science of nano-/micro joining
  • Process issues in nano/micro joining

The main goal of this special issue, “special issue of NMJ2018”, is to advance the new science and technology in the fields of e.g. micro-electronics, medical implants, sensing devices and packaging, which have an urgent need for advanced joining technologies to integrate, package and assemble nano- and micro-scale materials and components at ever-low temperatures. In the micro-devices and micro-systems, innovative microjoining are still needed to allow faster and more reliable fabrication and long life services. In the field of nanojoining, printed electronics, wearable and flexible electronics, 3D printing at nanoscale resolution and molecular electronics are the emergent applications in the coming decades. We invite investigators interested in nano- and microjoining innovation to contribute to this issue with 400CHF publication discount, the topics will cover all fields of NMJ2018.

Dr. Anming Hu
Prof. Dr. Jolanta Janczak-Rusch
Dr. Sano Tomokazu
Dr. Peng Peng
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Applied Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Nanojoining Microjoining Interfacial diffusions for micro- and nanojoining
  • Micro- and nanoscopic additive manufacturing
  • nano-/micro-scale materials
  • nano-/micro-scale devices
  • implantable medical devices
  • nano/micro joint characterization

Published Papers (23 papers)

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Research

Open AccessArticle Acquisition of Multi-Modal Images of Structural Modifications in Glass with Programmable LED-Array-Based Illumination
Appl. Sci. 2019, 9(6), 1136; https://doi.org/10.3390/app9061136
Received: 27 December 2018 / Revised: 11 March 2019 / Accepted: 12 March 2019 / Published: 18 March 2019
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Abstract
Ultrashort laser pulses can induce structural modifications in bulk glass, leading to refractive index change and scattering damage. As bright-field, dark-field, and phase imaging each provide complementary information about laser-induced structures, it is often desired to use multiple observations simultaneously. As described herein, [...] Read more.
Ultrashort laser pulses can induce structural modifications in bulk glass, leading to refractive index change and scattering damage. As bright-field, dark-field, and phase imaging each provide complementary information about laser-induced structures, it is often desired to use multiple observations simultaneously. As described herein, we present the acquisition of bright-field, dark-field, and differential phase-contrast images of structural modifications induced in glass by femtosecond laser pulses with an LED array microscope. The contrast of refractive index change can be enhanced by differential phase-contrast images. We also report on the simultaneous acquisition of bright-field and dark-field images of structural modifications in a glass with LED-array-based Rheinberg illumination. A single-shot color image is separated to obtain bright field and dark field images simultaneously. We provide an experimental demonstration on multi-modal imaging of structural modifications in a glass with an LED array microscope using temporally-coded illumination and color-coded illumination. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Microstructural Investigations of Low Temperature Joining of Q&P Steels Using Ag Nanoparticles in Combination with Sn and SnAg as Activating Material
Appl. Sci. 2019, 9(3), 539; https://doi.org/10.3390/app9030539
Received: 10 January 2019 / Revised: 31 January 2019 / Accepted: 1 February 2019 / Published: 6 February 2019
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Abstract
Quenching and partitioning (Q&P) steels show a good balance between strength and ductility due to a special heat treatment that allows to adjust a microstructure of martensite with a fraction of stabilized retained austenite. The final heat treatment step is performed at low [...] Read more.
Quenching and partitioning (Q&P) steels show a good balance between strength and ductility due to a special heat treatment that allows to adjust a microstructure of martensite with a fraction of stabilized retained austenite. The final heat treatment step is performed at low temperatures. Therefore, joining of Q&P steels is a big challenge. On the one hand, a low joining temperature is necessary in order not to influence the adjusted microstructure; on the other hand, high joint strengths are required. In this study, joining of Q&P steels with Ag nanoparticles is investigated. Due to the nano-effect, high-strength and temperature-resistant joints can be produced at low temperatures with nanoparticles, which meets the contradictory requirements for joining of Q&P steels. In addition to the Ag nanoparticles, activating materials (SnAg and Sn) are used at the interface to achieve an improved bonding to the steel substrate. The results show that the activating materials play an important role in the successful formation of joints. Only with the activating materials, can joints be produced. Due to the low joining temperature (max. 237 °C), the microstructure of the Q&P steel is hardly influenced. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Microstructure of Joint between Stranded Wire and Substrate Welded by Ultrasonic Welding
Appl. Sci. 2019, 9(3), 534; https://doi.org/10.3390/app9030534
Received: 31 December 2018 / Revised: 30 January 2019 / Accepted: 1 February 2019 / Published: 5 February 2019
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Abstract
In order to improvement electronic and mechanical properties, welding between stranded wires and terminals is important. However, welding methods to obtain high-quality joints using stranded wires are still limited. In this report, we applied ultrasonic welding to join a Cu stranded wire to [...] Read more.
In order to improvement electronic and mechanical properties, welding between stranded wires and terminals is important. However, welding methods to obtain high-quality joints using stranded wires are still limited. In this report, we applied ultrasonic welding to join a Cu stranded wire to a Cu substrate. Cross-sections of the weldments were taken and observed by several microscopy techniques to elucidate the weldability and soundness of the joints. After ultrasonic welding, each wire in the stranded wire was joined together at the region where the stranded wire was joined to the substrate without any defect. Each wire was welded through the Ag coating layer, and the stranded wire and the substrate was also welded through the outermost coating layers. It was found that ultrasonic welding is an efficient technique for producing high quality joints without any defect at the interface. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Transient Liquid Phase Bonding of Copper Using Sn Coated Cu MWCNT Composite Powders for Power Electronics
Appl. Sci. 2019, 9(3), 529; https://doi.org/10.3390/app9030529
Received: 31 December 2018 / Revised: 28 January 2019 / Accepted: 31 January 2019 / Published: 4 February 2019
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Abstract
In this paper, a novel transient liquid phase bonding material was fabricated by consequent electroless plating of Cu and Sn on a multi-walled carbon nanotube (MWCNT). The resulting Sn-Cu-MWCNT composites were used to join the Cu interconnects at 260°C. After 8 min of [...] Read more.
In this paper, a novel transient liquid phase bonding material was fabricated by consequent electroless plating of Cu and Sn on a multi-walled carbon nanotube (MWCNT). The resulting Sn-Cu-MWCNT composites were used to join the Cu interconnects at 260°C. After 8 min of reflow time, a complete transformation of Cu3Sn intermetallic compound (IMC) occurred, leaving a Cu/MWCNT-Cu3Sn /Cu joint capable of withstanding the high operating temperature. Due to flake-like morphology, the Sn-Cu-MWCNT composite particles were well packed with lesser voids. The shear strength of the Cu/Cu3Sn-MWCNT/Cu joint was measured as 35.3 MPa, thus exhibiting the scope for replacing conventional transient liquid phase (TLP) powders in the future. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Femtosecond Laser Irradiation of Carbon Nanotubes to Metal Electrodes
Appl. Sci. 2019, 9(3), 476; https://doi.org/10.3390/app9030476
Received: 12 December 2018 / Revised: 22 January 2019 / Accepted: 28 January 2019 / Published: 30 January 2019
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Abstract
Carbon nanotubes (CNTs) have excellent performance, which means that they could be better electrical conductors. However, the problem of the connection of CNTs to electrodes limits their application. Particularly, improving connection efficiency while ensuring the quality of the connection is a big challenge, [...] Read more.
Carbon nanotubes (CNTs) have excellent performance, which means that they could be better electrical conductors. However, the problem of the connection of CNTs to electrodes limits their application. Particularly, improving connection efficiency while ensuring the quality of the connection is a big challenge, because it is difficult to form Ohmic contact between CNTs and electrodes. To address this issue, we propose the use of a femtosecond laser to irradiate the contact surface between the CNTs and the electrodes to obtain a good connection quality and electrical performance. At the same time, since the laser-induced connection acts on all the contact surfaces in the irradiation area, the connection efficiency can be improved, which provides a new idea for the large-scale preparation of the connection. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Laser-Scribed Lossy Microstrip Lines for Radio Frequency Applications
Appl. Sci. 2019, 9(3), 415; https://doi.org/10.3390/app9030415
Received: 30 December 2018 / Revised: 17 January 2019 / Accepted: 21 January 2019 / Published: 26 January 2019
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Abstract
Laser-direct writing has become an alternative method to fabricate flexible electronics, whereas the resistive nature of laser-scribed conductors may distort the radio-frequency characteristics of circuits for high-frequency applications. We demonstrate that the transmission characteristics of microstrip lines are insensitive to the resistance of [...] Read more.
Laser-direct writing has become an alternative method to fabricate flexible electronics, whereas the resistive nature of laser-scribed conductors may distort the radio-frequency characteristics of circuits for high-frequency applications. We demonstrate that the transmission characteristics of microstrip lines are insensitive to the resistance of laser-scripted conductors when the sheet resistance is not above 0.32 Ω/□. On the other hand, the transmission and reflection characteristics of the MS lines can be simply modified through the accommodation of the resistance of the conductors, because a laser can trigger the sintering and melting of laser produced silver nanostructures. This could provide an alternative way to fabricate radio frequency (RF) resistors and promote their applications to flexible radio-frequency devices and systems. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Porosity Elimination in Modified Direct Laser Joining of Ti6Al4V and Thermoplastics Composites
Appl. Sci. 2019, 9(3), 411; https://doi.org/10.3390/app9030411
Received: 31 December 2018 / Revised: 20 January 2019 / Accepted: 23 January 2019 / Published: 26 January 2019
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Abstract
Hybrid lightweight components with strong and reliable bonding qualities are necessary for practical applications including in the automotive and aerospace industries. The direct laser joining method has been used to produce hybrid joints of Ti6Al4V and glass fiber reinforced polyamide (PA66-GF30). Prior to [...] Read more.
Hybrid lightweight components with strong and reliable bonding qualities are necessary for practical applications including in the automotive and aerospace industries. The direct laser joining method has been used to produce hybrid joints of Ti6Al4V and glass fiber reinforced polyamide (PA66-GF30). Prior to the laser joining process, a surface texturing treatment is carried out on Ti6Al4V to improve joint strength through the formation of interlock structures between Ti6Al4V and PA66-GF30. In order to reduce the generated micro-pores in Ti6Al4V-PA66-GF30 joints, a modified laser joining method has been proposed. Results show that only very few small micro-pores are generated in the joints produced by the modified laser joining method, and the fracture strength of the joints is significantly increased from 13.8 MPa to 41.5 MPa due to the elimination of micro-pores in the joints. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Effect of Aging Treatment on Microstructural Evolution of Rapidly Solidified Eutectic Sn-Pb Alloy Powders
Appl. Sci. 2019, 9(3), 392; https://doi.org/10.3390/app9030392
Received: 3 January 2019 / Revised: 21 January 2019 / Accepted: 22 January 2019 / Published: 24 January 2019
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Abstract
The microstructural stability of rapidly solidified eutectic Sn–Pb alloy solder powders was investigated through aging at room temperature (25 °C) and temperatures of 40 °C–120 °C. The coarsening behavior of the Pb-rich phase both at room and elevated temperatures was observed. The evident [...] Read more.
The microstructural stability of rapidly solidified eutectic Sn–Pb alloy solder powders was investigated through aging at room temperature (25 °C) and temperatures of 40 °C–120 °C. The coarsening behavior of the Pb-rich phase both at room and elevated temperatures was observed. The evident coarsening of the Pb-rich phase was detected upon storage after 40 days. At elevated temperatures, a similar sequence of Pb-rich phase coarsening was observed; however, it occurred substantially more quickly. Pb-rich coarsening rate kinetics at different temperatures were estimated using the Arrhenius equation. The apparent activation energy was 45.53 ± 4.23 KJ/mol, which indicates that grain boundary diffusion is a crucial mass transport mechanism controlling Pb-rich phase coarsening under annealing. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Femtosecond Pulse Laser Near-Field Ablation of Ag Nanorods
Appl. Sci. 2019, 9(3), 363; https://doi.org/10.3390/app9030363
Received: 4 January 2019 / Accepted: 18 January 2019 / Published: 22 January 2019
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Abstract
Ag nanorods (Ag NRs) with a mean aspect ratio of 3.9 were prepared through a wet-chemical method, and the absorption spectra for various aspect ratios were obtained. The morphology transformation of Ag NRs irradiated with a femtosecond pulse laser was investigated through transmission [...] Read more.
Ag nanorods (Ag NRs) with a mean aspect ratio of 3.9 were prepared through a wet-chemical method, and the absorption spectra for various aspect ratios were obtained. The morphology transformation of Ag NRs irradiated with a femtosecond pulse laser was investigated through transmission electron microscopy (TEM). The near-field ablation was dependent on the laser polarization and wavelength. Laser-induced high electric field intensity was observed at the ends, middle, and junctions of the Ag NRs under various ablation conditions. Through simulation, the evolution mechanism was analyzed in detail. The effect of laser polarization angle on plasmonic junction welding was also investigated. By controlling the electronic field distribution, several nanostructures were obtained: bone-shaped NRs, T-shaped NRs, dimers, trimers, curved NRs, and nanodots. This study suggests a potentially useful approach for the reshaping, cutting, and welding of nanostructures. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Joining of Carbon Fiber Reinforced Plastic to Aluminum Alloy by Reactive Multilayer Films and Low Power Semiconductor Laser Heating
Appl. Sci. 2019, 9(2), 319; https://doi.org/10.3390/app9020319
Received: 13 November 2018 / Revised: 3 January 2019 / Accepted: 8 January 2019 / Published: 17 January 2019
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Abstract
This study investigated the characteristics and strength of the dissimilar joints between carbon fiber reinforced plastic (CFRP) epoxy composites and aluminum alloys using two different heating methods, Ni/Al reactive multilayer films (RMF) and a low power continuous wave diode laser. To enhance the [...] Read more.
This study investigated the characteristics and strength of the dissimilar joints between carbon fiber reinforced plastic (CFRP) epoxy composites and aluminum alloys using two different heating methods, Ni/Al reactive multilayer films (RMF) and a low power continuous wave diode laser. To enhance the adhesion, the top resin layer of the CFRP and the surface of the aluminum alloy were patterned by femtosecond laser. Polycarbonate (PC) was used as a filler material during the joining processes. ANSYS simulation was applied to elucidate the thermal kinetics of the self-propagation reaction and the thermal profile, and evaluate the possibility of joining CFRP to aluminum using Ni/Al RMFs. The SEM image of the cross-section shows that melted PC flowed into the CFRP–aluminum alloy interface, suggesting strong mechanical bonding. A tensile strength of 9.5 MPa was reached using Ni/Al multilayers as heat sources, which provides a new way for joining CFRPs and aluminum alloys in space or under water. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Joining with Reactive Nano-Multilayers: Influence of Thermal Properties of Components on Joint Microstructure and Mechanical Performance
Appl. Sci. 2019, 9(2), 262; https://doi.org/10.3390/app9020262
Received: 13 December 2018 / Revised: 7 January 2019 / Accepted: 9 January 2019 / Published: 12 January 2019
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Abstract
Reactive nano-multilayers (RNMLs), which are able to undergo a self-heating exothermal reaction, can, e.g., be utilised as a local heat source for soldering or brazing. Upon joining with RNMLs, the heat produced by the exothermal reaction must be carefully adjusted to the joining [...] Read more.
Reactive nano-multilayers (RNMLs), which are able to undergo a self-heating exothermal reaction, can, e.g., be utilised as a local heat source for soldering or brazing. Upon joining with RNMLs, the heat produced by the exothermal reaction must be carefully adjusted to the joining system in order to provide sufficient heat for bond formation while avoiding damaging of the joining components by excessive heat. This heat balance strongly depends on the thermal properties of the joining components: a low thermal conductivity leads to heat concentration within the joining zone adjacent to the RNML, while a high thermal conductivity leads to fast heat dissipation into the components. The quality of the joint is thus co-determined by the thermal properties of the joining components. This work provides a systematic study on the influence of the thermal properties upon reactive joining for a set of substrate materials with thermal conductivities ranging from very low to very high. In particular, the evolution of the microstructure within the joining zone as a function of the specific time-temperature-profile for the given component material is investigated, focusing on the interaction between solder, RNML foil and surface metallisations, and the associated formation of intermetallic phases. Finally, the specific microstructure of the joints is related to their mechanical performance upon shear testing, and suggestions for optimum joint design are provided. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Evolution of Transient Liquid-Phase Sintered Cu–Sn Skeleton Microstructure During Thermal Aging
Appl. Sci. 2019, 9(1), 157; https://doi.org/10.3390/app9010157
Received: 19 December 2018 / Accepted: 27 December 2018 / Published: 4 January 2019
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Abstract
The evolution of the transient liquid-phase sintered (TLPS) Cu–Sn skeleton microstructure during thermal aging was evaluated to clarify the thermal reliability for die-attach applications. The Cu–Sn skeleton microstructure, which consists of Cu particles connected with Cu–Sn intermetallic compounds partially filled with polyimide resin, [...] Read more.
The evolution of the transient liquid-phase sintered (TLPS) Cu–Sn skeleton microstructure during thermal aging was evaluated to clarify the thermal reliability for die-attach applications. The Cu–Sn skeleton microstructure, which consists of Cu particles connected with Cu–Sn intermetallic compounds partially filled with polyimide resin, was obtained by the pressure-less TLP sintering process at 250 °C for 1 min using a novel Cu-solder-resin composite as a bonding material in a nitrogen atmosphere. Experimental results indicate that the TLPS joints were mainly composed of Cu, Cu6Sn5, and Cu3Sn in the as-bonded state, where submicron voids were observed at the interface between Cu3Sn and Cu particles. After thermal aging at 150, 175, and 200 °C for 1000 h, the Cu6Sn5 phase fully transformed into Cu3Sn except at the chip-side interface, where the number of the submicron voids appeared to increase. The averaged shear strengths were found to be 22.1 (reference), 22.8 (+3%), 24.0 (+9%), and 19.0 MPa (−14%) for the as-bonded state and specimens aged at 150, 175, and 200 °C for 1000 h, respectively. The TLPS joints maintained a shear strength over 19 MPa after thermal aging at 200 °C for 1000 h because of both the positive and negative impacts of the thermal aging, which include the transformation of Cu6Sn5 into Cu3Sn and the formation of submicron voids at the interface, respectively. These results indicate an excellent thermal reliability of the TLPS Cu–Sn skeleton microstructure. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Interface Growth and Void Formation in Sn/Cu and Sn0.7Cu/Cu Systems
Appl. Sci. 2018, 8(12), 2703; https://doi.org/10.3390/app8122703
Received: 30 November 2018 / Revised: 18 December 2018 / Accepted: 18 December 2018 / Published: 19 December 2018
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Abstract
In this work, the effects of electroplated Cu (EP Cu) and Cu addition (0.7%) in Sn solder on the intermetallic compounds (IMCs) growth and void formation were clarified by comparison with solder joints comprising of high purity Cu (HP Cu) substrate and pure [...] Read more.
In this work, the effects of electroplated Cu (EP Cu) and Cu addition (0.7%) in Sn solder on the intermetallic compounds (IMCs) growth and void formation were clarified by comparison with solder joints comprising of high purity Cu (HP Cu) substrate and pure Sn solder. After aging processes, a new IMC, Cu3Sn, was formed at the interface, in addition to Cu6Sn5 formed in the as-soldered joints. The EP Cu and Cu addition (0.7%) both had limited effects on the total IMCs thickness. However, the effects varied on the growth behaviors of different IMCs. Comparing to the void-free interface between Sn and HP Cu, a large number of voids were observed at the Cu3Sn/Cu interface in Sn/EP Cu joints. The formation of these voids may be induced by the impurities and fine grain, which were introduced during the electroplating process. The addition of Cu suppressed the inter-diffusion of Cu and Sn at the interface. Consequently, the growth of the Cu3Sn layer and formation of voids were suppressed. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessFeature PaperArticle The Effect of Interfacial Ge and RF-Bias on the Microstructure and Stress Evolution upon Annealing of Ag/AlN Multilayers
Appl. Sci. 2018, 8(12), 2403; https://doi.org/10.3390/app8122403
Received: 25 October 2018 / Revised: 21 November 2018 / Accepted: 22 November 2018 / Published: 27 November 2018
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Abstract
The present study addresses the structural stability and mass outflow of Ag10nm/Ge1nm/AlN10nm nanomultilayers (NMLs) during thermal treatments in different atmospheres (Ar and air). The nanomultilayers were obtained by magnetron sputtering under different deposition conditions (with [...] Read more.
The present study addresses the structural stability and mass outflow of Ag 10 nm/Ge 1 nm/AlN 10 nm nanomultilayers (NMLs) during thermal treatments in different atmospheres (Ar and air). The nanomultilayers were obtained by magnetron sputtering under different deposition conditions (with and without the RF (Radio-Frequency)-bias application). The microstructure of the as-deposited and thermally treated NMLs were analyzed by XRD and SEM techniques, deriving morphology, microstructure and internal stress. Bias application during the deposition is found to create highly disordered interfaces and to have a very strong influence on the morphology and structural evolution with temperature of the nano-multilayers. Complete multilayer degradation is observed for the bias sample when annealed in Ar at 700 C, while the periodic multilayer structure is preserved for the non-bias samples. Structural and morphological changes are observed starting from 400 C, accompanied with Ag surface migration. The highest Ag amount on the surface is detected in air atmosphere for bias and non-bias samples annealed at temperatures as high as 700 C. The presence of Ge is found to strongly hinder the Ag surface migration. Ag outflow is measured to take place only through the network of surface cracks in the AlN barrier formed upon heating. The crack formation and Ag migration are discussed together with the stress relaxation. The present study demonstrates the feasibility to tailor the stress state of as-deposited NML structures and observe different structural evolution depending on the initial conditions. This paves the way for advanced experimental strategies to tailor directional mass outflow in nanoconfined filler systems for advanced nano-joining applications. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle A Modified Interposer Fabrication Process by Copper Nano-Pillars Filled in Anodic Aluminum Oxide Film for 3D Electronic Package
Appl. Sci. 2018, 8(11), 2188; https://doi.org/10.3390/app8112188
Received: 24 October 2018 / Revised: 4 November 2018 / Accepted: 4 November 2018 / Published: 8 November 2018
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Abstract
Though copper nano-pillars (CNPs) filled in anodic aluminum oxide (AAO) film has been developed for many years, the high pore-filling percentage in AAO is still a bottleneck. We have demonstrated a new electrodeposition method to fill CNPs in AAO without the seed layer [...] Read more.
Though copper nano-pillars (CNPs) filled in anodic aluminum oxide (AAO) film has been developed for many years, the high pore-filling percentage in AAO is still a bottleneck. We have demonstrated a new electrodeposition method to fill CNPs in AAO without the seed layer which is required in the traditional electrodeposition process. CNPs with uniform heights were obtained and the pore-filling percentage reached up to 97.5%. Low current density is beneficial for the high pore-filling percentage due to the uniform growing rate in different nanoscale pores. The high temperature increased the diffusion velocity of ions and enhanced the pore filling percentage but also corroded the AAO film simultaneously. Results showed that CNPs grains with <220> orientation were fabricated. Electrodeposition with low electric current could contribute to the forming of CNPs with (220) preferred orientation due to the promotion of dehydration reduction processes. The thermal conductivities of Cu-AAO interposers reaches 92.34 W/(m·K) and 3.19 W/(m·K) in vertical and horizontal directions, respectively. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Electrical and Mechanical Properties of Ink Printed Composite Electrodes on Plastic Substrates
Appl. Sci. 2018, 8(11), 2101; https://doi.org/10.3390/app8112101
Received: 26 September 2018 / Revised: 25 October 2018 / Accepted: 26 October 2018 / Published: 1 November 2018
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Abstract
Printed flexible electrodes with conductive inks have attracted much attention in wearable electronics, flexible displays, radio-frequency identification, etc. Conventional conductive inks contain large amount of polymer which would increase the electrical resistivity of as-printed electrodes and require high sintering temperature. Here, composite electrodes [...] Read more.
Printed flexible electrodes with conductive inks have attracted much attention in wearable electronics, flexible displays, radio-frequency identification, etc. Conventional conductive inks contain large amount of polymer which would increase the electrical resistivity of as-printed electrodes and require high sintering temperature. Here, composite electrodes without cracks were printed on polyimide substrate using binder-free silver nanoparticle based inks with zero-dimensional (activated carbon), one-dimensional (silver nanowire and carbon nanotube) or two-dimensional (graphene) fillers. The effect of fillers on resistivity and flexibility of printed composite electrodes were evaluated. The graphene filler could reduce the resistivity of electrodes, reaching 1.7 × 10−7 Ω·m after low power laser sintering, while the silver nanowire filler improved their flexibility largely during bending tests. The microstructural changes were examined to understand the nanojoining process and their properties. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Influence of Interfacial Intermetallic Growth on the Mechanical Properties of Sn-37Pb Solder Joints under Extreme Temperature Thermal Shock
Appl. Sci. 2018, 8(11), 2056; https://doi.org/10.3390/app8112056
Received: 25 September 2018 / Revised: 15 October 2018 / Accepted: 22 October 2018 / Published: 25 October 2018
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Abstract
Solder joints in thermally uncontrolled microelectronic assemblies have to be exposed to extreme temperature environments during deep space exploration. In this study, extreme temperature thermal shock test from −196 °C to 150 °C was performed on quad flat package (QFP) assembled with Sn-37Pb [...] Read more.
Solder joints in thermally uncontrolled microelectronic assemblies have to be exposed to extreme temperature environments during deep space exploration. In this study, extreme temperature thermal shock test from −196 °C to 150 °C was performed on quad flat package (QFP) assembled with Sn-37Pb solder joints to investigate the evolution and growth behavior of interfacial intermetallic compounds (IMCs) and their effect on the pull strength and fracture behavior of Sn-37Pb solder joints under extreme temperature environment. Both the scallop-type (Cu, Ni)6Sn5 IMCs at the Cu lead side and the needle-type (Ni, Cu)3Sn4 IMCs at the Ni-P layer side changed to plane-type IMCs during extreme temperature thermal shock. A thin layer of Cu3Sn IMCs was formed between the Cu lead and (Cu, Ni)6Sn5 IMC layer after 150 cycles. The growth of the interfacial IMCs at the lead side and the Ni-P layer side was dominated by bulk diffusion and grain-boundary diffusion, respectively. The pull strength was reduced about 31.54% after 300 cycles. With increasing thermal shock cycles, the fracture mechanism changed from ductile fracture to mixed ductile–brittle fracture, which can be attributed to the thickening of the interfacial IMCs, and the stress concentration near the interface caused by interfacial IMC growth. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Mechanical Property of Sn-58Bi Solder Paste Strengthened by Resin
Appl. Sci. 2018, 8(11), 2024; https://doi.org/10.3390/app8112024
Received: 19 September 2018 / Revised: 13 October 2018 / Accepted: 16 October 2018 / Published: 23 October 2018
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Abstract
Sn-58Bi solder has been widely used for microelectronics packaging due to its low melting point temperature, good wetting performance, good mechanical properties, and low cost. Compared with Sn-Bi solder alloy and Sn-Pb solder alloy, the strength and plasticity of Sn-Bi solder are not [...] Read more.
Sn-58Bi solder has been widely used for microelectronics packaging due to its low melting point temperature, good wetting performance, good mechanical properties, and low cost. Compared with Sn-Bi solder alloy and Sn-Pb solder alloy, the strength and plasticity of Sn-Bi solder are not enough, due to the higher brittleness of bismuth, which thus limits the application of Sn-Bi solder. In order to improve the properties of Sn-Bi solder, a novel solder paste strengthened with resin was developed by mixing epoxy resin (ER) with Sn-58Bi solder, which enhanced the joint strength at a low cost. Aimed at the electronic industry, in this study, the spreadability of the novel solder paste was investigated, and the mechanical properties and microstructure of solder joints after reflow soldering were tested and analyzed. The results showed that when the content of epoxy resin was in the optimum range, the shear strength was significantly higher, reaching nearly twice that of Sn-58Bi solder alone. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Study on Microstructure and Fatigue Damage Mechanism of 6082 Aluminum Alloy T-Type Metal Inert Gas (MIG) Welded Joint
Appl. Sci. 2018, 8(10), 1741; https://doi.org/10.3390/app8101741
Received: 10 September 2018 / Revised: 19 September 2018 / Accepted: 20 September 2018 / Published: 27 September 2018
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Abstract
In this experiment, the T-joint of a 6082 aluminum alloy was welded by metal inert gas (MIG) welding and a fatigue test was carried out at room temperature. The mechanisms of generating pores and of fatigue fracture in welded joints are revealed in [...] Read more.
In this experiment, the T-joint of a 6082 aluminum alloy was welded by metal inert gas (MIG) welding and a fatigue test was carried out at room temperature. The mechanisms of generating pores and of fatigue fracture in welded joints are revealed in the case of incomplete penetration. There are two main types of pores: pores that are not welded and pores that are near the upper weld line of the weld. During welding, bubbles in the molten pool are adsorbed on the surface oxide film that is not penetrated, and cannot be floated to form pores; since it is a T-shaped welded joint, the molten pool is overhanged during welding, thereby forming pores near the fusion line. The fatigue strength of the welded joint based on the S–N curve at 107 cycles is estimated to be 37.6 MPa, which can reliably be predicted in engineering applications. Fatigue tests show that fatigue cracks are all generated in the pores of the incomplete penetration, and it and the pores form a long precrack, which leads to large stress concentration, and the fracture occurs under a small applied load. Grain morphology around the pores also has a large effect on the fatigue properties of the T-weld joint. In the weld’s fatigue fracture, it was found that the crack stable-extension zone exhibited ductile-fracture characteristics, and the instantaneous fault zone is composed of a large number of tear-type dimples showing ductile fractures. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Study on the Reliability of Sn50Pb49Sb1/Cu Solder Joints Subjected to γ-ray Irradiation
Appl. Sci. 2018, 8(10), 1706; https://doi.org/10.3390/app8101706
Received: 24 August 2018 / Revised: 10 September 2018 / Accepted: 13 September 2018 / Published: 20 September 2018
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Abstract
Cosmic radiation has always been the most obvious barrier to planetary travels, especially in long-duration deep space exploration missions. Therefore, the reliability of satellite materials and the requirements of satellite miniaturization have received considerable attention. In this paper, the effect of γ-ray [...] Read more.
Cosmic radiation has always been the most obvious barrier to planetary travels, especially in long-duration deep space exploration missions. Therefore, the reliability of satellite materials and the requirements of satellite miniaturization have received considerable attention. In this paper, the effect of γ-ray irradiation on the reliability of Sn50Pb49Sb1/Cu solder joints was investigated. It was found that the influence of γ-ray irradiation on the thickness and morphology of the intermetallic compound layer in Sn50Pb49Sb1/Cu was not obvious. However, the formation and growth of micro-voids and micro-cracks was observed in Pb-based solid solutions. Due to the Compton effect, the γ-ray photon could knock the electron out of its orbit, which created the energetic electron. The accumulation of dislocated atoms and lattice vacancies generated by energetic electrons could be the main factor that caused the formation of micro-voids and micro-cracks. The pull force of Sn50Pb49Sb1/Cu solder joints was reduced by 22% after being irradiated at the dose rate of 0.25 Gy(Si)/s for 960 h. Fractographic analysis showed that after irradiation, the fracture type of solder joints was still ductile but the ductility of the solder joints decreased with slightly inconspicuous dimples. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Influence of Preheating Temperature on Cold Metal Transfer (CMT) Welding–Brazing of Aluminium Alloy/Galvanized Steel
Appl. Sci. 2018, 8(9), 1659; https://doi.org/10.3390/app8091659
Received: 20 August 2018 / Revised: 10 September 2018 / Accepted: 11 September 2018 / Published: 14 September 2018
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Abstract
Bead-on-plate cold metal transfer (CMT) brazing and overlap CMT welding–brazing of 7075 aluminium alloy and galvanized steel at different preheating temperatures were studied. The results indicated that AlSi5 filler wire had good wettability to galvanized steel. The preheating treatment can promote the spreadability [...] Read more.
Bead-on-plate cold metal transfer (CMT) brazing and overlap CMT welding–brazing of 7075 aluminium alloy and galvanized steel at different preheating temperatures were studied. The results indicated that AlSi5 filler wire had good wettability to galvanized steel. The preheating treatment can promote the spreadability of liquid AlSi5. For the overlap CMT welding–brazed joint, the microstructure of the joint was divided into four zones, namely, the interfacial layer, weld metal zone, zinc-rich zone, and heat affected zone (HAZ). The load force of the joints without preheating and 100 °C preheating temperature was 8580 N and 9730 N, respectively. Both of the joints were fractured in the fusion line with a ductile fracture. Further increasing the preheating temperature to 200 °C would decrease the load force of the joint, which fractured in the interfacial layer with a brittle fracture. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessFeature PaperArticle Self-Powered Fast Brazing of Ti-6Al-4V Using Ni/Al Reactive Multilayer Films
Appl. Sci. 2018, 8(6), 985; https://doi.org/10.3390/app8060985
Received: 26 May 2018 / Revised: 8 June 2018 / Accepted: 12 June 2018 / Published: 15 June 2018
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Abstract
Self-powered brazing of Ti-6Al-4V was performed using Ni/Al reactive multilayer films (RMFs) as self-propagated heat resources. BAlSi-4 was first coated on Ti-6Al-4V by plasma welding, then alternating layers of Ni and Al were successfully deposited on BAlSi-4 up to 32.9 μm thick with [...] Read more.
Self-powered brazing of Ti-6Al-4V was performed using Ni/Al reactive multilayer films (RMFs) as self-propagated heat resources. BAlSi-4 was first coated on Ti-6Al-4V by plasma welding, then alternating layers of Ni and Al were successfully deposited on BAlSi-4 up to 32.9 μm thick with e-beam deposition. The joint microstructure was investigated and the AlNi and Ni5Al3 phases were identified in the RMF. The cause for the two phases was determined to be differences in the diffusivity of Ni and Al, ultrafast brazing time, and faster cooling at the interface between brazing filler metal and the RMF. The maximum temperature of 683 °C was reached in the brazed joint, with a total RMF thickness of 135 μm, which is more than sufficient to melt the BAlSi-4 brazing material. The maximum bonding strength obtained was 10.6 MPa, with a self-power brazing procedure conducted in a minute. It is possible to further improve the bonding strength by using more ductile RMFs and/or modifying the bonding interface configuration. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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Open AccessArticle Diode Laser Welding/Brazing of Aluminum Alloy to Steel Using a Nickel Coating
Appl. Sci. 2018, 8(6), 922; https://doi.org/10.3390/app8060922
Received: 18 May 2018 / Revised: 29 May 2018 / Accepted: 30 May 2018 / Published: 4 June 2018
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Abstract
Joining Al alloy to steel is of great interest for application in the automotive industry. Although a vast number of studies have been conducted to join Al to steel, the joining of Al to steel is still challenging due to the formation of [...] Read more.
Joining Al alloy to steel is of great interest for application in the automotive industry. Although a vast number of studies have been conducted to join Al to steel, the joining of Al to steel is still challenging due to the formation of brittle Fe–Al intermetallic compounds. In this work, the microstructure and mechanical properties of the dissimilar Al/steel joints with and without a nickel coating are comparatively investigated. A homogenous reaction layer composed of FeZn10 and Fe2Al5 is formed at the interface in the joints without Ni coating, and the joint facture load is only 743 N. To prevent the formation of brittle Fe2Al5, Ni electroplated coating is applied onto a steel surface. It has been shown that a nonhomogeneous reaction layer is observed at the interfacial region: Ni5Zn21 is formed at the direct irradiation zone, while Al3Ni is formed at the fusion zone root. The microhardness of the interfacial layer is reduced, which leads to the improvement of the joint mechanical properties. The average fracture load of the Al/Ni-coated steel joints reaches 930 N. In all of the cases, failure occurs at the Ni coating/fusion zone interface. Full article
(This article belongs to the Special Issue Selected Papers from the NMJ2018)
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