bluuebunny/crossref_metadata_2025 huggingface dataset:
The Development of Superplasticity and Deformation Mechanism Maps in an Ultrafine-Grained Magnesium Alloy
Authors: Kawasaki Megumi , Figueiredo Roberto B. , Langdon Terence G.
Published: November 2016

Magnesium alloys with refined grain structure are often superplastic at elevated temperatures with maximum elongations up to more than 1000%. The superplastic behavior of this material agrees with deformation by grain boundary sliding. Dislocation climb becomes the rate controlling mechanism at higher stresses but the rate controlling mechanism at lower stresses is not fully documented. This report examines the development of superplasticity in a magnesium ZK60 alloy and shows that an increase in stress exponent and decrease in elongation takes place at low stresses. Deformation mechanism maps are constructed considering Regions I, II and III and Coble creep.
The Interface Character Distribution and Intergrannular Corrosion Resistance of Duplex Stainless Steel UNS S32304
Authors: Zhang Jian Sheng , Zhu Yan Li , Fang Xiao Ying , Yin Wen Hong , Qin Cong Xiang
Published: November 2016

The duplex stainless steels (UNS S32304) after solid solution annealing at two different temperature (1323K and 1573K) were subjected to the same cold rolling with ε =3 and subsequent annealing for 230 min at 1323 K . The corresponding interface character distribution (ICD) were determined by electron backscatter diffraction (EBSD). The results show that a larger population of phase boundaries (PB) having K-S orientation relationship (OR) between the neighboring δ and γ grains was introduced and therefore higher intergrannular corrosion resistance (ICR) were resulted in the specimen initially solid-solution annealed at 1573K.
The Role of the Nd/Zn Ratio on the Stability of Mg-Zn-Nd Clusters and the Evolution of Texture in Two Mg-Zn-Nd Alloys during Annealing
Authors: Sanjari Mehdi , Farkoosh Amir Rezaei , Kabir Abu S.H. , Su Jing , Jung In Ho , Yue Stephen , Amirkhiz Babak Shalchi , He You Liang
Published: November 2016

Texture evolution in two magnesium alloys, Mg-4%Zn-1%Nd and Mg-1%Zn-1%Nd (weight percentage), was studied after rolling and the subsequent isothermal annealing. The finish rolling was completed in a single pass with a thickness reduction rate of ~30% at 100 °C and a rolling speed of 1000 m/min. After cooling to room temperature, the rolled samples were annealed at 350 °C for different annealing times. Upon annealing, the maximum intensity of the basal pole texture decreases as recrystallization progresses. In the Mg-1Zn-1Nd alloy (with a high Nd/Zn ratio), texture weakening is maintained even after complete recrystallization and grain coarsening, while in the Mg-4Zn-1Nd alloy, texture strengthening occurs after grain coarsening, and a single peak replaces the double split basal peaks. In the Mg-1Zn-1Nd alloy, grain coarsening is accompanied by a bimodal grain size distribution, whereas in the Mg-4Zn-1Nd alloy, the grain coarsening leads to a uniform grain size distribution. TEM investigations show the formation of the Zn and Nd rich clusters at early stage of annealing in both alloys. During recrystallization, these clusters were dissolved in the Mg-4Zn-1Nd alloy, but they are more stable in the Mg-1Zn-1Nd alloy. In our opinion, the formation of these stable clusters is one of the main factors for texture weakening of the Mg-Zn-RE alloys.
Microstructure and Residual Stress in Rotary Friction Welded Dissimilar Metals of AA7020 Aluminium Alloy with 316L Steel
Authors: Gan Wei Min , Hofmann Michael , Ventzke Volker , Randau Christian , Huang Yuan Ding , Kriele Armin , Brokmeier Heinz Guenter , Mueller Martin
Published: November 2016

Rotary friction welding (RFW) was used in the current study to join the dissimilar metals AA7020-T6 aluminium alloy and 316L steel. Neutron diffraction was performed to investigate the texture gradient around the weld line and to map the residual stress over the whole specimen. The texture analysis showed a weak shear component near the bond line of AA7020-T6-T6 side which indicated a plastic deformation of AA7020-T6 during welding. The shear bands were also observed in optical microstructures. Relatively high tensile residual stresses were observed near the bond line on the AA7020-T6 side, which were in-homogeneously distributed from the perimeter to the rod centre, while high compressive residual stresses were found in the sample centre at the bond line in the 316L steel.
Residual Stress Measurements on IN718 Fatigue Specimens Using X-Ray Diffraction Techniques
Authors: Gao Yi Fei , Wang Shu Lan
Published: November 2016

Residual stress measurements were successfully performed on the representative IN718 fatigue specimens by X-Ray Diffraction. All surface residual stresses were found to be compressive. A stress gradient normal to the surface was observed on all specimens. The residual stresses tended to become less compressive with increasing depth into the parts. Residual stress measurement is the special requirement for NADCAP CRITERIA AC 7101/7. In this paper, residual stress measurements were successfully performed on two IN718 low cycle fatigue test specimens.
Microstructure-Property Relationships in Medium-Mn Steels with Metastable Retained Austenite
Authors: Grajcar Adam , Morawiec Mateusz
Published: November 2016

The study addresses relationships between the microstructure and mechanical properties of thermomechanically processed carbide-free bainitic steels containing 3% and 5% Mn. A simulated thermomechanical processing using Gleeble equipment and thermomechanical hot strip rolling were applied to produce fine-grained mixtures of blocky-type and interlath metastable retained austenite embeded between bainitic ferrite laths. To monitor the transformation behaviour of retained austenite into strain-induced martensite interrupted tensile tests were applied. The identification of morphological features of retained austenite and strain-induced martensite was carried out using scanning electron microscopy (SEM) equipped with EBSD (Electron Backscatter Diffraction). The amount of retained austenite was determined by the EBSD technique. It was found that manganese content strongly affects mechanical stability of retained austenite resulting in a different degree of TRIP effect in the investigated alloys and subsequent mechanical properties of produced sheets.
Casting of an Mg Alloy Clad Strip Using a Twin Roll Caster Equipped with a Scraper
Authors: Haga Toshio , Okamura Kentaro , Nishida Shinichi , Watari Hisaki , Matsuzaki Kunio
Published: November 2016

Casting of an Mg alloy clad strip was attempted with a twin roll caster equipped with a scraper in an oxidizing atmosphere. The base strip was AM60 and the overlay strip was AZ121. The AM60 strip was cast with a roll, and the upper side of the strip was scribed by the scraper. The molten AZ121 was poured on the scribed AM60 strip. The scribed surface of AM60 contacted the molten metal of AZ121 without exposure to the atmosphere. Therefore, the scribed surface was not oxidized. Most of the AZ121 strip was solidified by the other roll. The casting speed was 30 m/min. The roll load was 0.05 kN/mm. The roll speed was very high and the roll load was very small. However, the strips were bonded, and they did not peel with bending until breaking. The interface between the two strips was clear. When AM60 was on the outer side, the results of the V-bending test and the Erichsen test were better. These results mean that the ductility of AZ121 was improved by cladding with AM60.
High-Temperature Deformation Behavior of (Mo0.85Nb0.15)Si2 Crystals with C40/C11b Lamellar Microstructure
Authors: Hagihara Koji , Araki Haruka , Ikenishi Takaaki , Nakano Takayoshi
Published: November 2016

The effect of alloying element (such as Cr, Zr, and Ir) addition on the high-temperature creep deformation behavior of C40/C11b lamellar-structured (Mo0.85Nb0.15)Si2 silicide crystals was examined. The results indicated that these additions all lead to a decrease in the steady-state creep strain rate (SSCR) when the applied stress is parallel to the lamellar interface. To clarify the origin of this, the dependence of the creep deformation behavior on the microstructure was determined in detail. As a result, it was found that the C40 phase acts as a strengthening phase during the deformation of the C40/C11b duplex-phase crystals. The variant-1-type C11b phase grains, whose loading orientation is parallel to [001], also acts as an effective strengthening component. The decrease in SSCR by Cr or Zr addition is attributed to the increase in volume fraction of those C40 phase and C11b-V1 grains. The refinement of microstructure by Ir addition was also found to result in a modest decrease in the SSCR.
Material and Mechanical Aspects of CMAS Damage Progression on Thermal Barrier Coatings and its Non-Destructive Detection
Authors: Hayashi Yukie , Lokachari Siddharth , Yamagishi Satoshi , Okazaki Masakazu
Published: November 2016

Thermal barrier coatings (TBCs) on turbine blades in gas turbine engines are in some cases damaged at high temperatures exceeding 1200°C by calcium-magnesium-alumino-silicates (CMAS) resulting from the ingestion of siliceous minerals. In this study, material interaction between molten CMAS and yttria-stabilized zirconia (YSZ) was investigated using a single crystal YSZ material and a synthetic CMAS product. Reaction between the molten CMAS and YSZ was significant at high temperature resulting in the infiltration of CMAS into the dense bulk-YSZ. The extent of interaction between CMAS and YSZ was found to be dependent on the crystallographic plane of the YSZ. The change in elastic stiffness due to the CMAS infiltration was also found by using a vibrating reed technique. The CMAS infiltrated layer had elastic stiffness higher by approximately five times of the non-infiltrated one. An attempt to detect the CMAS damage progression was also made through an AC impedance method. The proposed AC impedance technique is expected to be a useful technique to evaluate the CMAS infiltration as well as the associated delamination of TBC top coat.
Complex Cell Physiology on Topographically and Chemically Designed Material Surfaces
Authors: Nebe J. Barbara , Moerke Caroline , Staehlke Susanne , Finke Birgit , Schnabelrauch Matthias , Anselme Karine , Helm Christiane A. , Frank Marcus , Rebl Henrike
Published: November 2016

A crucial factor for ingrowth of permanent implants in the bone is the rapid cellular acceptance. The topographical features often follow mechanical aspects for implant stability. But several of these implants fail due to insufficient cell adhesion. Cells are able to perceive the physico-chemical properties of their surrounding and to pass these signals into the cell to modulate their adhesion structures, growth or production of extracellular matrix. However, the complex cell physiology at the material interface is not yet fully understood, particular on stochastically structured topographies resulting from industrial production. We could find out that corundum blasted titanium hampered the organization of actin filaments inside the cells, clustered adhesion components, e. g. beta-1 integrins and tensin, and the cells bridged the valleys which reduces cell-substrate contacts. These morphological changes strongly diminished the mineralization of osteoblasts. To shed light on cause and effect we reduced the physical complexity of the material surface by introduction of regular micro-structures (pillars, grooves) using deep reactive ion etching. Now it was more obvious what cells are doing on sharp edged topographies ‒ the actin filaments of our cells were clustered around the pillars. As a result the intracellular calcium signaling and the protein synthesis were impaired. Our recent findings indicated an attempted phagocytosis of the micro-pillars by osteoblasts. Therefore we conclude that implants used in orthopedic surgery should avoid any sharp-edged topographical features that could induce phagocytosis by the surrounding cells, which is an unnecessarily energy consuming process.
Long-Term Performance Analysis of Geomembrane Considering Stress Cracking Resistance
Authors: Jeon Han Yong
Published: November 2016

In this study, key properties of polyethylene resin and HDPE GM were tested for comparing their stress crack behaviors. Stress cracking time was differed from each type of resins and products. The failure times of ESCR test were too long compared to SP-NCTL's. The SP-NCTL results of RWOA was failed earlier than RWA‘s, GM1’s and GM2’s. But there was no difference between each sample of the results of ESCR test within short term testing duration. The ESCR test was influenced by stress relaxation during the test. The SP-NCTL test is reasonable for verifying stress cracking behavior and construction quality control. According to this study, ESCR test is not appropriate for determining the stress crack behavior, but SP-NCTL test is better test method for predicting the stress crack behaviors of HDPE GM.
Local Surface Phase Stability during Cyclic Oxidation Process
Authors: Calmunger Mattias , Eriksson Robert , Chai Guo Cai , Johansson Sten , Högberg Jan , Moverare Johan
Published: November 2016

Surface properties are essential for many engineering material ́s design issues, such as fatigue and corrosion performances. Austenitic stainless steels used in high-temperature applications, as for instance components in biomass-fired power plants, need sufficient corrosion resistance. At temperatures above 600 °C and in water vapor environment, Cr-vaporization will create Cr-depletion, causing a local change in chemical composition. This local change in chemical composition leads to phase transformation in some austenitic stainless steels. This paper reports the surface properties regarding the local phase transformation during thermal cycling in water vapor environment. Three commercial austenitic stainless steels are investigated, AISI 304, AISI 316L and Sandvik SanicroTM 28. The thermal cycling was performed up to 650 °C in a 15 mol.% water vapor environment. AISI 304 shows local surface phase transformation related to martensitic transformation due to locally changed chemical composition and increase in the martensitic transformation temperature (Ms). However, the other two austenitic stainless steels don’t show this martensitic transformation. The phase transformation and oxidation is discussed using microstructural investigations methods such as x-ray diffraction (XRD), electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS).
Influence of the Processing Variables on the Microstructure Evolution of a Bainitic Carbide-Free Steel
Authors: Taboada M.C. , Gutiérrez I. , Jorge-Badiola D. , van Bohemen S.M.C. , Hisker F. , Paul Georg
Published: November 2016

New trends focused on achieving higher performance steels has led to a so-called 3rd Generation Advanced High Strength Steels (AHSS), in which the typical polygonal ferrite found in TRIP steels as a matrix phase is replaced by harder phases as Carbide-Free Bainite (CFB) and/or (tempered) martensite. Besides, large volume fractions of retained austenite (R.A.) with adequate stability are aimed for to improve the formability of the steels. Si containing steels are regarded as the most suitable to retard cementite formation and consequently reach high volume fractions of RA. In this work, CFB annealing schedules were applied to dilatometer samples of Fe-0.22C-2.0Mn-1.3Si. The overaging temperature TB was varied between 390 oC and 480 oC, and other processing variables investigated were the austenitizing temperature Taus, and the overaging holding time tB. The annealed samples analyzed with LOM, FEG-SEM, EBSD and X-ray diffraction techniques show that markedly different complex microstructures made up of bainite, ferrite, MA phase and retained austenite (R.A) are accomplished depending on the specific thermal cycle. These results are described in detail and discussed in relation to the dilatometry measurements.
The Effect of Sample Preparation on the Microstructure of Austenitic-Ferritic Stainless Steel
Authors: Juuti Timo , Uusikallio Sampo , Kaijalainen Antti , Heinonen Esa , Tun Nyo Tun , Porter David A.
Published: November 2016

Sample preparation of metastable austenitic-ferritic steels can have a significant effect on the apparent microstructure due to the transformation of austenite to martensite (γ - α'). As a result, these steels often have a complex microstructure with ferrite and martensite, which have relatively similar crystal structures, making it very difficult to analyse. However, the quantitative analysis of such microstructures and the effect of the sample preparation are very important for the further study of the steel. In this research, the effect of sample preparation in metastable austenitic-ferritic stainless steel was studied by using three different sample preparation methods. In addition to conventional mechanical etching with colloidical silica and electropolishing, focused ion beam (FIB) milling was used to create an optimal sample surface to be further analysed with electron backscatter diffraction (EBSD). Micrographs were obtained from each sample before and after sample preparation using field emission scanning electron microscopy (FESEM) and laser scanning confocal microscopy (LSCM), and the microstructure was analysed using EBSD. The surface flatness required for good EBSD analysis was significantly better using FIB milling than mechanical polishing, while electropolishing results in the greatest topography and an arched sample surface. The amount of martensite was found to be dependent on the sample preparation: least martensite was formed during electropolishing, while surprisingly mechanical polishing and FIB milling resulted in equal amounts of martensite.
Evaluation of Rolling Contact Fatigue by Using an X-Ray Diffraction Ring Analyzer
Authors: Kamura Naoya , Fujita Takumi , Sasaki Toshihiko
Published: November 2016

In this report, rolling contact fatigue (RCF) progression in two-cylinder type RCF testing is evaluated by using an X-ray diffraction ring analyzer, which can rapidly obtain tri-axial stress and the orientation of crystallite.
The large compressive and three principal stresses on the RCF surface are observed under boundary lubrication. It is considered that the crack occurrence and its propagation by asperity contact of surface roughness are caused by residual principal shear stress and the repeated contact stress. In addition, the behavior of RCF progression from the point of view of the X-ray measurements is similar for the driving and driven specimen until the generation of peeling begins. This supports the conclusion of Kaneta et al. that the RCF progression for the driven cylinder is the same as that for driving cylinder until peeling occurs.
Intermetallic Phases in New Steels
Authors: Bleck Wolfgang , Song Wen Wen , Zimmermann Alexander
Published: November 2016

Al containing intermetallic phases have been evaluated in various bcc and fcc steels. Attractive application options have been derived for hot working tools steels with respect to a reduction of resource critical alloying elements and in cold formable steels by the combined density reduction and strength increase.
Microstructural Characterization and Mechanical Properties of Stainless Steel Inlay Welded Dissimilar Materials
Authors: Kim Jun Hyong , Amanov Auezhan , Kang Myeong Sung , Kim Hak Doo , Pyun Young Sik , Choi Yoon Suk
Published: November 2016

This present work was carried out to characterize the microstructure and mechanical properties of austenitic stainless steel (SS) 316L to dissimilar welding of Inconel 52 and Inconel 82 fillers that were treated by ultrasonic nanocrystalline surface modification (UNSM) technique. The microstructure and hardness map of the specimens were characterized by optical microscope (OM) and micro-hardness tester. The increase in hardness and refinement in grain size after UNSM treatment were found for the SS 316L/52 and SS 316L/82. In addition, the induced compressive residual stress in the surface layer of base SS 316L was measured. It is expected that the increased hardness into several microns in depth and modified microstructure with a severe plastically deformed surface layer by UNSM technique can increase the resistance to corrosion and extend the service life of pressurized water reactors (PWRs).
Effect of Large Strain on Texture Formation Behavior of AZ80 Magnesium Alloy during High Temperature Deformation
Authors: Kim Kwon Hoo , Okayasu Kazuto , Fukutomi Hiroshi
Published: November 2016

In previous study, the formation behavior of texture and microstructure in AZ80 magnesium alloy under high temperature deformation was investigated. It was found that the basal texture was formed at stress of more than 15-20MPa and the non-basal texture was formed at stress of less than 15-20MPa. This means that stress of 15-20MPa is the change point of deformation mechanism. Therefore, in this study, uniaxial compression deformation of AZ80 magnesium alloy was carried out at high temperature deformation (stress of 15-20MPa). Behaviors of microstructure and texture development are experimentally studied. The material used in this study is a commercial magnesium alloy extruded AZ80. The uniaxial compression deformation is performed at temperature of 723K and strain rate 3.0×10-3s-1, with a strain range of between-0.4 and-1.3. Texture measurement was carried out on the compression planes by the Schulz reflection method using nickel filtered Cu Kα radiation. EBSD measurement was also conducted in order to observe spatial distribution of orientation. As a result of high temperature deformation, the maximum value of the flow stress is observed at the true stress-strain curves, and the main component of texture and the accumulation of pole density vary depending on deformation condition.
Diamond Based Schottky Photodiode for Radiation Therapy In Vivo Dosimetry
Authors: Prestopino Giuseppe , Santoni Enrico , Verona Claudio , Verona Rinati Gianluca
Published: November 2016

Diamond has long been considered as a suitable material for the fabrication of radiation detectors due to its outstanding physical properties. Even more so in the specific case of radiation therapy dosimetry applications, where the near-tissue equivalence radiation absorption, good spatial resolution and radiation hardness are required. Recently, a synthetic single crystal diamond dosimeter was developed at “Tor Vergata” University in cooperation with PTW-Freiburg, showing excellent dosimetric properties. Such a device was thus commercialized (microDiamondTM, PTW-type 60019) and widely accepted by the medical physics community, due to its reproducibility, reliability, accuracy and versatility. In this work, a novel diamond based dosimeter for in vivo application developed in our laboratories is presented. A basic dosimetric characterization of detector performances was performed under irradiation with 60Co and 6 MV photon beams. Response stability, short and long term reproducibility, fading effect, linearity with dose, dose rate dependence, and temperature dependence were investigated. The detector response was found to be reproducible and dose rate independent in the range between 0.5 and 5 Gy/min. Its temperature dependence was within 0.5% between 25 and 38 ◦C, and negligible fading effect was observed. The obtained results indicate the proposed novel diamond device as a promising candidate for in vivo dosimetry in radiation therapy application.
Structure Formation in Ni Superalloys during High-Speed Direct Laser Deposition
Authors: Klimova-Korsmik Olga G. , Turichin Gleb A. , Zemlyakov Evgeniy , Babkin Konstantin , Petrovsky Pavel , Travyanov Andrey
Published: November 2016

Additive technologies are replacing the conventional methods of casting and subsequent time-consuming machining because of its high productivity. Resent engineering development in the field of additive manufacturing allows increasing assortment of useful powder materials. Technology of high-speed direct laser deposition (HSDLD) is a one of most perspective new technologies. It allows realizing heterophase process during the manufacturing, which there is process of partial melting of used powder is realized. The product is formed from a metal powder, which is supplied by compressed gas-powder jet directly into the laser action zone, wherein the jet can be as coaxial and as non-coaxial.
Ni-based alloys found their application in many industrial areas, mostly there are used engine systems, aircraft and shipbuilding, aeronautics. The unique combination of operational characteristics depending on the type of alloy makes them promising materials. Heating and cooling rates during direct laser deposition determine structure and affect on its properties. Research is focused on structure and phase formation within technological process of HSDLD for Ni-base superalloys. Mechanical tests were carried out on the static tensile test, microhardness was measured. Based on research results the high-speed direct laser deposition technology could be used for manufacturing of products from different Ni-based alloys without subsequent heat treatment.
CD8αβ+ γδ T Cells: A Novel T Cell Subset with a Potential Role in Inflammatory Bowel Disease
Authors: Kadivar Mohammad , Petersson Julia , Svensson Lena , Marsal Jan
Published: November 2016

γδ T cells have been attributed a wide variety of functions, which in some cases may appear as contradictory. To better understand the enigmatic biology of γδ T cells it is crucial to define the constituting subpopulations. γδ T cells have previously been categorized into two subpopulations: CD8αα+ and CD8− cells. In this study we have defined and characterized a novel subset of human γδ T-cells expressing CD8αβ. These CD8αβ+ γδ T cells differed from the previously described γδ T cell subsets in several aspects, including the degree of enrichment within the gut mucosa, the activation status in blood, the type of TCRδ variant used in blood, and small but significant differences in their response to IL-2 stimulation. Furthermore, the novel subset expressed cytotoxic mediators and CD69, and produced IFN-γ and TNF-α. In patients with active inflammatory bowel disease the mucosal frequencies of CD8αβ+ γδ T cells were significantly lower as compared with healthy controls, correlated negatively with the degree of disease activity, and increased to normal levels as a result of anti–TNF-α therapy. In conclusion, our results demonstrate that CD8αβ+ γδ T cells constitute a novel lymphocyte subset, which is strongly enriched within the gut and may play an important role in gut homeostasis and mucosal healing in inflammatory bowel disease.
Thermal and Electrical Characterizations of Ultra-Thin Flexible 3YSZ Ceramic for Electronic Packaging Applications
Authors: Zhao Xin , Jagannadham K. , Reainthippayasakul Wuttichai , Lanagan Michael. T. , Hopkins Douglas C.
Published: November 2016

This paper presents thermal and electrical characterizations of an ultra-thin flexible 3YSZ (3 mol% Yttria Stabilized Zirconia) ceramic substrate to explore its potential for electronic packaging applications. The thicknesses of the ultra-thin 3YSZ substrates were 20 μm and 40 μm. The flexible thin ceramic substrate can provide not only better modulus for higher robustness in manufacturing, especially in Z-axis direction of modules, but also low thermal resistance for high density 2D (two dimensional) / 3D (three dimensional) power module packaging applications. To better understand the thermal and electrical properties of the ultra-thin flexible ceramic, different measurements were employed. Thermal conductivity was measured at different temperatures by 3-omega method, the results were verified by thermo-reflectance measurement at room temperature. Relative permittivity was measured from 100 Hz to 10 MHz, with dielectric losses determined by dielectric spectroscopy. The dielectric breakdown of the ultra-thin flexible 3YSZ was measured, from room temperature to 150 °C. Weibull analysis was performed on 20 measurements for each temperature. The test results showed that the thermal conductivity of 3YSZ decreased from 3.3 W/mK at 235 K to 2.2 W/Mk at 600 K. The relative permittivity decreased from 30.9 to 27.3 for higher frequencies for both substrates with different thickness. The temperature-dependence of relative permittivity and dielectric loss was studied. The results showed that these two parameters increased slowly from −65 °C to 150 °C, but more repidly from 175 °C to 250 °C. The dielectric breakdown decreased at higher temperature, from 5.76 kV to 2.64 kV for thickness of 20 μm, 7.84 kV to 3.36 kV for thickness of 40 μm. SEM (Scanning Electron Microscopy), EDS (Energy-dispersive X-ray Spectroscopy) and XRD (X-ray Powder Diffraction) analysis was performed to compare the microstructure of 3YSZ ultra-thin substrate and that of AlN (Aluminum Nitride) substrate. The microstructure of 3YSZ consisted of smaller round particles and that of AlN contained larger columnar particles. FEA (Finite Element Analysis) simulations were also applied to demonstrate the thermal properties of 3YSZ in simplified model of power modules. Though the measurement results showed that it did not meet expectations for high temperature power modules, the present work showed potential applications of the ultra-thin 3YSZ substrates in low voltage power modules, LED modules.
Higher Efficiency Power Module Solutions by Chip Embedding
Authors: Essig Kay S , Chiu CT , Kuo Jarris , Chen Phidia , Yannou Jean-Marc
Published: November 2016

The development in communication handheld devices has pushed the demand for packages with high level of functionality and complexity at the same time smaller package outline and decreased package thickness. Embedding active dies and/or passive components into the substrate is fulfilling these integration requirements, but embedding can have further beneficial effects (electrical performance, thermal dissipation, shielding) that deliver more benefit for embedding (1).

Whereas embedding dies in substrates seems a simple concept, it can come with strong advantages as found in the described case for Power Modules in terms of electrical performance and thermal dissipation.

In this paper we shall report the development of embedded technologies for Power Modules and compare electrical performance, thermal dissipation and reliability results with other Power Module package types. We shall report on an intelligent power module for server applications up to 1.5kW consisting of a driver IC and 2 MOSFETs using embedded die in substrate technology in high volume manufacturing.

We will describe the development of next generation embedding technologies for Power Modules, their expected benefits and respective application targets together with simulation results. We conclude with a brief overview of the challenges that come with embedded packaging supply chain.
Direct write lithography approach for Panel Level Package
Authors: Matsui Hiroshi , Nagao Tatsuya , Norimitsu Yoshinao
Published: November 2016

Fan-out processing a is booming technology at wafer level packaging. However, chip last process in fan-out gives great difficulty to lithography. At the same time, the industry is looking for increasing substrate size in order to reduce production cost. Direct write technology shall be the key lithography process having both flexibility and compatibility for large size substrate.
A deeper understanding on the motion behaviors of wire during ultrasonic wedge-wedge bonding process
Authors: Long Yangyang , Dencker Folke , Wurz Marc , Feldhoff Armin , Twiefel Jens
Published: November 2016

Ultrasonic wire bonding is a dominating interconnection technique that has been applied in packaging industry for decades. The phenomena at the wire/substrate interface and the wire/tool interface, however, are not clear yet. Specifically, the motion behaviors of the wire during the bonding process have to be deeply understood. In this project, the relative motion amplitudes at the wire/tool interface and the self-cleaning efficiency at the wire/substrate interface are investigated via the analysis of an artificially coated layer. For each experiment, a thin layer made of a specific material was coated onto the surface of a 400 μm wire by physical vapor deposition. The change of thicknesses of the layer was observed by a scanning electron microscope after the bonding process. The results indicated a complex relative motion behavior at the wire/tool interface. The relative motion amplitude at the fillets contact regions is higher than that at the other contact perimeter regions while the amplitude at the central area is the lowest. The insignificant influence of a 200 nm aluminum oxide layer on the bonding quality demonstrated the high self-cleaning efficiency of the wedge-wedge bonding process.
Advances in Wire Bonding Technology for Overhang Applications
Authors: Shah Aashish , Schulze Gary , Mendoza Nestor , Yang J.H. , Ellenberg Rob , Qin Ivy , Chylak Bob
Published: November 2016

Wire bonding is the most popular interconnect technology and the workhorse of the semiconductor packaging industry. Wire bonding is widely used for 3D packaging in which multiple dies are often stacked vertically in a ‘stacked die’ configuration. In such packages, one or more dies may be unsupported in an ‘overhang’ (e.g. cantilever beam) configuration. Wire bonding on an overhang die causes die deflection. If not optimized, it may lead to improper ball shape, inconsistent looping, pad crack and die crack issues. Therefore, careful process optimization is needed to have the best outcome in wire bonding performance. This optimization is often tedious and time-consuming. Moreover, recent trends towards minimizing package size (e.g. ultra-thin dies) and increasing number of die stacks add to the challenges of optimizing a wire bonding process for overhang devices.

This paper examines the challenges of wire bonding on overhang devices. Finite element analysis (FEA) of overhang devices is presented. Die deflection data obtained from the FEA correlates well with the experimental results obtained on the ball bonder. The FEA results show that die deflection increases significantly with decreasing die thickness and increasing overhang distance. Other factors such as substrate thickness, and bonding temperature also effect die deflection, although less significantly than die thickness and overhang distance. Various considerations for optimizing a ball bonding process on overhang devices are discussed. Experimental results of ball bonding optimization on 50 μm and 75 μm thick overhang devices with different overhang configurations are presented.
In-situ measuring module for transfer molding process monitoring
Authors: Kahle R. , Braun T. , Bauer J. , Becker K.-F. , Schneider-Ramelow M. , Lang K.-D.
Published: November 2016

While Moore's Law is slowing down heterogeneous integration and System-in-Package (SiP) are taking up the challenge towards further miniaturization. To ensure reliability of these packages often encapsulation by transfer molding is used – providing a highly productive and cost effective device housing. Though transfer molding is the dominant process for microelectronics encapsulation, the process details are typically not accessible directly but only via machine settings. To understand more of the mold process further research needs to be conducted to get inside information from the process. A sensor based system was developed to in-situ measure transient material data and process parameters. The temperature of the tool and melt front, the cavity pressure and cure related dielectric material data was measured with a first prototype.

Summarized this paper presents the development of a sensor based system to in-situ measure characteristic material properties and process parameters in a transfer mold machine. The in-situ measurement tool allows a live documentation, optimization and knowledge extension of transfer mold processes parallel to FEM simulation and external measuring like DSC analysis. The sensor approach can lead to material driven self-adjusting transfer mold machines with an economized process.
Alternative Metallurgies for MEMS Lid Seal
Authors: Shearer Catherine
Published: November 2016

MEMS devices are a segment of the electronics industry enjoying explosive growth. With the advent of the internet of things (IoT), the trajectory for growth will continue to be steep and price pressures on both the devices and packaging will be intense.

Current MEMS packaging schemes rely heavily on an architecture that employs a metal-can or laminate “lid” attached to the device package with a solder ring. This ring serves to connect the package elements together mechanically and to protect the device from noise (electronic or acoustic) and environmental damage.

Like most modern electronic devices, MEMS devices are subject to the challenges imposed by the requirement for lead-free packaging. As with many devices, solder connections formed within the package have a similar composition, and therefore a similar reflow profile, to the solder used to attach the packaged components to a substrate. Devices that yield well at the manufacturer are thus susceptible to field failure at the assembly site induced by remelting of the solder within the package during assembly reflow. Unlike in SIP packages where the solder joints in the module are often encased in mold compound, the ring seal in MEMS devices is exposed and unreinforced resulting in failures such as lid shift, solder flow or flux contamination in the device cavity, and package deconstruction - particularly during rework. These type of post-fabrication yield losses can be very costly.

Transient liquid phase (TLPS) sintering paste compositions are a new class of solder replacement materials that can be processed at typical reflow temperatures, but which do not remelt when subjected to subsequent thermal excursions. TLPS pastes combine solder alloy particles and reactive metal particles in proportions such that the solder ‘thermosets’ during a typical solder reflow cycle. This ‘thermosetting’ behavior results in a joint that does not remelt at the original reflow temperature, and thus enables the highly reliable electrical interconnect essential for assemblies that will undergo subsequent reflow excursions.

TLPS pastes are similar to solders in many respects. The electrical, thermal and mechanical performance is similar to conventionally used tin-based solders. The TLPS pastes are stored and applied like solder pastes. The reflow cycles used to form the TLPS paste joints are also similar to those for forming solder joints. However, unlike solder, TLPS materials do not change shape during reflow or wet substrates beyond the deposition footprint. Also unlike solder, the metals within the bulk of the TLPS interconnect react with one another resulting in a stable interconnect with a thermally robust bonding structure to joining surfaces, even after subsequent thermal cycles. These attributes present both unique opportunities and unique challenges for addressing MEMS lid seal applications. This paper will explore the key material and engineering challenges for implementation of TLPS paste in MEMS lid seal applications.
The Die Embedded and RDL structure on the high density substrate (i-THOP®) for mobile application
Authors: Kyozuka Masahiro , Yoshida Tatsuro , Shimizu Noriyoshi , Tanaka Koichi , Koyama Tetsuya
Published: November 2016

The current trend in the electronics industry is one of increased computing performance, combined with a seemingly unending demand for portability and increased miniaturization; this is especially evident in the significant changes to the semiconductor device. To sustain the performance-improvement trend without increasing total cost, the partitioning of single die into a multi-chip architecture is widely studied in industry. These partitioned chips are then integrated into a single system-in-package (SiP).

However, partitioning a single die into multiple split die causes two major challenges. The first is that it creates the need for very high density die to die interconnection. This interconnection is needed to provide enough routing density between the multiple die. Based on design studies, it believes that 2μm line and 2μm space is required in the package substrate.

The second challenge is created by the increase in the overall die size. After partitioning the single die, each resulting smaller die must have its own I/O circuits, and effectively increases the total die area. This increase is a penalty, as mobile devices have a limited package size. When comparing a conventional package on package (PoP), the SiP requires a higher pin count with a finer pitch connection between the die and the memory. This finer pitch is needed to have enough I/Os, but within a limited package size to support mobile devices.

To overcome these challenges, the structure of i-THOP® with POP pad, named “i-THOP® with Die embedded +ReDestribution Layer(RDL) structure”, has been developed. Herein, i-THOP® (integrated Thin film High density Organic Package) is a type of high-density substrate A key aspect to development of Die embedded +RDL is forming the multiple redistribution layers (RDL) over die and the fine pitch via connection. To achieve this, the proper material set was selected based on stress simulations and basic experiments. Regarding the manufacturing process, a conventional printed-circuit board (PCB) production line was used to minimize production cost. This article reports the manufacturing process and characteristics of the structure.
Voltammetric Detection of Low Copper Concentrations in Nickel Plating Baths
Authors: Pavlov Michael , Coffin Mitchell , Lin Danni , Shalyt Eugene
Published: November 2016

Nickel electroplating is widely used in semiconductor manufacturing, primarily during the packaging stage. It is not used as a final coating, but instead as a barrier layer to prevent formation of copper–tin intermetallic compounds that affect the reliability of solder joints. The nickel is deposited from baths containing nickel salt (in relatively high concentrations), boric acid, and other ions.

The quality of the deposited nickel is highly dependent on the composition of the plating bath. Metallic contaminants are acceptable when their concentrations are below approximately 30 ppm. Copper, lead, zinc, and cadmium, even in relatively small quantities (higher than 30 ppm) produce a dull, black, or skip plate condition in the low-current-density areas. These metals may be removed from the plating solution by low-current-density dummy plating, but a sensitive and accurate analytical method must be used to determine when to treat the bath. Copper is considered a main contaminant due to its higher concentrations in the bath and its most detrimental effect on the nickel deposit. To prevent plating defects, the bath contaminants must be monitored.
Addressing Flux Dip Challenges for 3D Integrated Large Die, Ultra-fine Pitch Interconnect
Authors: Marsan-Loyer C. , Danovitch D. , Boyer N.
Published: November 2016

The requirement for closely coupled, highly integrated circuits in the semiconductor industry has spawned alternative packaging innovations such as 2.5D/3D integration. The incredible potential of this alternative comes with great challenges, not the least of which is the unprecedented reduction in package interconnection pitch. Market acceptance of new fine-pitch microelectronic products is strongly dependent upon the development of flawless assembly processes that align with the traditional Moore-like expectation of higher performance without cost penalty. One such process is the application of flux to the interconnect surfaces in order to achieve effective joining. Insufficient flux quantity or flux activity can impede the formation of solid, reliable joints, while excessive quantities or activity can cause solder bridging or difficulties with downstream operations such as residue cleaning or underfill reinforcement. This delicate balance, already complex for traditional chip joining, is further challenged by the geometrical and spatial reductions imposed by pitch miniaturization, especially where large die, with over 100,000 interconnects, are concerned. This paper presents an overall development protocol to evolving a flux dipping operation to production-level thermocompression assembly of large die with ultra-fine pitch (60 μm) copper pillar interconnections. After reviewing the state of the art for fluxing technology and detailing the specific technical issues, we present and defend the chosen flux application approach with its corresponding parameters of interest. Physical and chemical characterization results for selected flux material candidates are reported in conjunction with an analysis of how their properties correlate to the flux dip application parameters. As part of this fundamental understanding, we investigate and report on flux dip coating behaviour and how it compares to other industrial dip coating applications. Finally, the results of process assembly experiments in a production-type environment are reviewed and discussed with respect to the previous characterizations. These experiments span downstream assembly process compatibility (i.e. cleaning and underfill) as well as product reliability.
Electrodeposited copper-graphite composites for low-CTE integrated thermal structures
Authors: Dwarakanath Shreya , Raj P. Markondeya , Demir Kaya , Smet Vanessa , Sundaram Venky , Tummala Rao
Published: November 2016

Emerging high-power and high-temperature electronic modules require thick copper structures for power-supply, thermal vias, heat-spreaders, and also as carriers or lead-frames for high-power packages. Such structures should coexist with glass and other low-CTE substrates to meet high-temperature performance, dimensional stability and superior device interconnection reliability with low stresses and warpage. The primary challenge with these packages arises from the coefficient of thermal expansion (CTE) mismatch between the conductors and the substrates. Cu-graphite composites with glass-matched CTE are explored to address this challenge through analytical modeling of properties such as CTE, Young's modulus and thermal conductivity, FEM predictions of glass warpage and stresses, process development to deposit copper-graphite composite films with high graphite loading of 64 vol. %, and warpage measurements using shadow-moiré. Results indicate that Cu-graphite composites can mitigate the warpage and stress issues in high-temperature and high-power packages.
Effects of Silicon Wafer Bump Pad Structures on Solder and Cu Pillar Flip-Chip Reliability
Authors: Asoy Shirley , Exon Scott , Zhu Liping , Moon Peter , Carroll Michael , Pan Shannon
Published: November 2016

Solder and Cu pillar flip-chip silicon die technologies have been widely used in chip to package mobile module products. During the early design phase, integrated circuit (IC) designers usually apply standard bump design rules, due to lack of information on the reliability of the metal layer stack-up with different bumping processes. However, module reliability data has demonstrated that the stack-up and thickness of the metal layers in a silicon die has a great effect on package stresses, especially for large area Cu pillar flip chip die. In this paper, the effects of bump pad structures on solder and Cu pillar bump reliability have been investigated. A 3D mechanical stress model was developed to compare and optimize various bump structures. A test vehicle with die and module was designed and assembled in a volume production environment. Assembly in-line data was collected and analyzed, and is presented in this paper. Reliability testing and failure analysis were performed to verify the failure modes. Guidelines for designing solder and Cu Pillar Flip-chip bump pad structures have been developed, and are presented in this paper.