MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Volume 46 , Issue 11
Showing 1-40 articles out of 40 articles from the selected issue
  • King-Ning Tu, Jong-ook Suh, Albert Tzu-Chia Wu, Nobumichi Tamura, Chih ...
    2005 Volume 46 Issue 11 Pages 2300-2308
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    Spontaneous Sn whisker growth on Cu leadframe finished with Pb-free solder is a serious reliability problem in electrical and electronic devices. Recently, Fortune magazine had an article to describe the urgency of the problem. The spontaneous growth is an irreversible process, in which there are two atomic fluxes driven by two kinds of driving force. There are a flux of Cu atoms and a flux of Sn atoms. The Cu atoms diffuse from the leadframe into the solder finish driven by chemical potential gradient to form intermetallic compound of Cu6Sn5 in the grain boundaries of the solder, and the growth of the compound at room temperature generates a compressive stress in the solder. To relieve the stress, a flux of Sn atoms driven by the stress gradient diffuses away to grow a spontaneous Sn whisker which is stress-free. The typical industry solution is to insert a diffusion barrier of Ni between the Cu and solder to prevent the diffusion of Cu into the solder. It is insufficient, because we have to uncouple the irreversible processes and stop both the fluxes of Cu and Sn. A solution is presented here.
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  • Yoshiharu Kariya, Tomokazu Niimi, Tadatomo Suga, Masahisa Otsuka
    2005 Volume 46 Issue 11 Pages 2309-2315
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    Micro-bulk fatigue testing developed to investigate the fatigue lives and damage mechanisms of Sn–3.0Ag–0.5Cu and Sn–37Pb solder alloys. The fatigue life of micro-bulk solder obeyed Manson–Coffin’s empirical law, and the fatigue ductility exponents were about 0.5 for both Sn–Ag–Cu and Sn–Pb alloys. The fatigue life of Sn–3.0Ag–0.5Cu alloy was 10 times longer than that of Sn–37Pb alloy under symmetrical cycling at 298 K, although fatigue resistance of Sn–3.0Ag–0.5Cu alloy was not very superior under asymmetrical wave and elevated temperature condition. The fatigue crack was developed from extrusion and intrusion of slip band in Sn–3.0Ag–0.5Cu alloy, while the crack was observed at colony boundary and grain boundary in Sn–37Pb alloy. The difference in damage mechanism may affect the susceptibility to fatigue life test condition of reversibility.
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  • Qiang Yu, Jae-Chul Jin, Do-Seop Kim, Masaki Shiratori
    2005 Volume 46 Issue 11 Pages 2316-2321
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    The use of Sn–Zn–Bi and Sn–Zn solders is increasing because of their low cost and low melting point. Therefore, it is important to ensure the fatigue strength of Sn–Zn–Bi and Sn–Zn solder joints. In this study, the mechanical fatigue strength of Sn–Zn–Bi and Sn–Zn solder joints was evaluated by using chip scale package (CSP) specimens. The influence of surface treatment on the fatigue strength was investigated by using specimens with Ni/Au or pre-flux on a Cu-pad. These specimens were aged at 85, 125 and 150°C for 500 and 1000 h to investigate the influence of the appearance of intermetallic compounds at the joint interface. Through a series of isothermal mechanical shear fatigue tests and finite element method (FEM) analyses, it was found that the fatigue lives of Sn–Zn–Bi and Sn–Zn solder joints were greatly affected by the aging temperature. In particular, when Sn–Zn–Bi and Sn–Zn solder joints with Ni/Au plating of the Cu-pad were aged at a temperature above 125°C, the fatigue strength decreased remarkably in comparison with the specimens without Ni/Au plating.
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  • Sun-Yun Cho, Young-Woo Lee, Kyoo-Seok Kim, Young-Jun Moon, Ji-Won. Lee ...
    2005 Volume 46 Issue 11 Pages 2322-2328
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    In order to evaluate the reliability of Sn–8 mass%Zn–3 mass%Bi (hereafter, Sn–8Zn–3Bi) solder, thermal shock tests (temperature range: from 233 to 353 K) and high temperature humidity tests (test condition: 353 K, 85% relative humidity) were conducted. The PCB (Printed Circuit Board) pads were finished by OSP (Organic Solderability Preservative), Sn and Ni/Au. The electric part for test was QFP (Quad Flat Package), and the lead was plated by Sn–3 mass%Bi. The joint strength was estimated by pull testing, and Zn-phase behavior in solder joint was examined.
    The pull strengths of Sn–8Zn–3Bi joints in the as-soldered state were measured to be about 16N, irrespective of the PCB pad coatings. After thermal shock testing (hereafter, TS test) up to 1000 cycles, the pull strengths decreased to around 14N. Meanwhile, after high temperature humidity testing (hereafter, HTH test) up to 1000 h, the pull strengths deceased to around 6N, irrespective of the PCB pad coatings. The reason for the drastic decrease of pull strength after the HTH test was proven to be a crack that was observed along the zinc oxide-phase. The Zn-phase in the Sn–8Zn–3Bi solder changed from a separate acicular shape to a lined-up branched arrangement after HTH tests of 1000 h.
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  • Ikuo Shohji, Kiyokazu Yasuda, Tadashi Takemoto
    2005 Volume 46 Issue 11 Pages 2329-2334
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    A tensile test was conducted to evaluate thermal fatigue resistances of Sn–Ag and several Sn–Ag–Cu lead-free solder alloys. The test is based on the strain rate change method to obtain a strain rate sensitivity index, m. The m values were investigated at various strains during the tensile test until fracture. The plots of m and strain where m is measured showed a linear relationship. Therefore, the m value at zero strain, m0, and the gradient of the fitting line, k, were obtained by extrapolation. Using m0 and k values investigated, an estimation of the thermal fatigue resistance of the solder joint was attempted. The ranking of the reciprocals of m0 and k in the solders is relatively in good agreement with that of the thermal fatigue resistance of the solder joints, and thus m0 and k can be indexes to develop a new lead-free solder with the excellent thermal fatigue resistance. Moreover, the influences of the aging treatment on m0, k and the microstructure of the solder were also investigated.
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  • Takehiko Takahashi, Susumu Hioki, Ikuo Shohji, Osamu Kamiya
    2005 Volume 46 Issue 11 Pages 2335-2343
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    The low-cycle fatigue behavior of Sn–3.5 mass%Ag, Sn–0.7 mass%Cu lead-free solders and Sn–37 mass%Pb solder were investigated at a strain rate of 0.1%/s with a non-contact extensometer at room temperature (22±3°C). In addition, the relationship between the surface features in the low-cycle fatigue test and the fatigue life of those solders were investigated by image processing. The fatigue lives of Sn–3.5 mass%Ag and Sn–0.7 mass%Cu were better than that of Sn–37 mass%Pb. The low-cycle fatigue behavior on each solder followed Coffin–Manson equation. The surface deformation in fine wrinkles was observed in the low-cycle fatigue test at each solder. The surface features for each solder were evaluated by image processing from the surface deformation. The surface features in the low-cycle fatigue test did not appear until under 10% of the fatigue life for Sn–3.5 mass%Ag, until 10% of the fatigue life for Sn–0.7 mass%Cu, and until 20% of the fatigue life for Sn–37 mass%Pb.
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  • Joo Won Lee, Zin Hyoung Lee, Hyuck Mo Lee
    2005 Volume 46 Issue 11 Pages 2344-2350
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    Quaternary Sn–Ag–Cu–Ni composite solders were made with several different ratios of Cu/Ni to study the effect of Cu/Ni on the type of intermetallic compound phase at the joint interface. The eutectic solders of Sn–3.5Ag and Sn–3.5Ag–0.7C (numbers are all in mass% unless specified otherwise) were used as references together with the ternary composite solder of Sn–3.0Ag–7.0Cu tested previously. When the ratio of excess Cu/Ni alloyed in the original composite solder was 7:3, 6:4 and 5:5, the reinforcing intermetallic compound (IMC) was (Cu,Ni)6Sn5. When the ratio was Cu:Ni=3:7, both phases of (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 showed up while only the (Ni,Cu)3Sn4 phase was observed in the solder with a Cu:Ni ratio of 1:9. For the interfacial reaction of the eutectic Sn–3.5Ag–0.7Cu with the rolled Ni substrate, the thick (Cu,Ni)6Sn5 layer was formed on the thin (Ni,Cu)3Sn4 layer. The addition of Ni was effective to suppress the formation of the thick (Cu,Ni)6Sn5 IMC. When the (CuxNi1−x)6Sn5 IMC layer was formed, the value of x was lager than 0.6 while for the case of (NyCu1−y)3Sn4 the value of y was larger than 0.8. The addition of Ni enhanced the bonding properties and retarded the growth of IMC. In the Ni bearing composite solder, there was no significant sedimentation of reinforcing particles during reflow, which took place commonly in the other composite solders. Wettability and mechanical properties of the Ni bearing solders were also compared.
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  • Shinji Ishikawa, Eiji Hashino, Taro Kono, Kohei Tatsumi
    2005 Volume 46 Issue 11 Pages 2351-2358
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    The bumps for flip chip interconnection are becoming smaller and smaller. Since lead-free solders became popular, Ni-based under bump metallization (UBM) has attracted attention in recent years because of their slower reaction rate than traditional Cu-based UBM. However, there is little data concerning the solid state reaction between small lead-free solder bumps and Ni-based UBM. In this work, Sn–3Ag–0.5Cu and Sn–3.5Ag solder bumps were fabricated with 110-μm-diameter solder balls on electrolytic Ni, and the growth kinetics of intermetallic compound (IMC) layers and the morphology of bumps during long-term aging were investigated. The IMC layer exhibited parabolic growth, and the activation energy values for the Sn–3Ag–0.5Cu or Sn–3.5Ag solder/Ni UBM were obtained. The growth rate accelerated at 463 K or above. (Ni,Cu)3Sn4 or Ni3Sn4 IMC was formed mainly at the solder/Ni interface after long-term aging. Large voids were formed at the solder/IMC interface at 463 K or above. The voids are the result of stress by volume expansion due to IMC growth. Coarse Ag3Sn grains were observed adjacent to the voids and contributed to void initiation.
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  • Jaesik Lee, Jae-Pil Jung, Chu-Seon Cheon, Yunhong Zhou, Michael Mayer
    2005 Volume 46 Issue 11 Pages 2359-2365
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    Flip chip bumping by stencil printing method using a new composition of solder paste, Sn–1.8%Bi–0.8%Cu–0.6%In, all in mass%, was investigated. Sn–3.5%Ag, Sn–37%Pb and Sn–36%Pb–2%Ag were selected as references for the experiment. The solder pastes were printed on the under bump metallization (UBM) of a Si-wafer using a stencil, where diameter and thickness of the stencil opening were 400 and 150 μm, respectively. The UBM deposit comprised 0.4 μm each of Al, Ni and Cu, and 20 nm of Au from bottom to top of the metallization, sequentially. The printed paste bumps were reflow soldered in air, and the peak soldering temperature of Sn–1.7Bi–0.8Cu–0.6In and Sn–3.5Ag was 523 K and of Sn–37Pb and Sn–36Pb–2Ag was 503 K. From the experimental results the solder bumps of Sn–1.8Bi–0.8Cu–0.6In alloys were well-formed with a mean height of 260 μm. The shear strength of Sn–1.8Bi–0.8Cu–0.6In at 523 K (as-reflowed) showed the highest value of 6.5N followed by those of Sn–3.5Ag, Sn–37Pb and Sn–36Pb–2Ag solders. After 1000 h aging, while the shear strength of the Sn–1.8Bi–0.8Cu–0.6In showed 27% decrease compared to as-reflowed conditions, it was still 15–30% higher than those of Sn–37Pb, Sn–36Pb–2Ag and Sn–3.5Ag solders. Intermetallic compounds (IMCs) formed on the interface between solder and UBM were (Cu,Ni)6Sn5. As aging time went on up to 1000 h, the content of Ni in the IMC changed from 6.6% at initial stage (as-reflowed) to 13.5% at final stage (1000 h aging).
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  • Dae-Gon Kim, Seung-Boo Jung
    2005 Volume 46 Issue 11 Pages 2366-2371
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    The interfacial microstructure of Sn–0.7Cu solder with ENIG (electroless Ni/immersion Au) was studied using scanning electron microscopy (SEM), electron probe micro analyzer (EPMA) and transmission electron microscopy (TEM). (Cu,Ni)6Sn5 intermetallic compound (IMC) layer was formed at the interface between the solder and Ni–P under bump metallurgy (UBM) upon reflow. The thickness of the (Cu,Ni)6Sn5 IMC layer increased with isothermal aging time. Two distinctive layers, P-rich and Ni–Sn–P, were additionally found from TEM observation. Analytical studies using energy dispersive spectrometer (EDS) equipped in TEM revealed that the composition of the P-rich layer is close to that of a mixture of Ni3P and Ni, while that of the Ni–Sn–P layer is analogous to the P-rich layer but containing a small amount of Sn in it. The shear force of the joints decreased during isothermal aging. The decrease of the shear force should be mainly due to the microstructural degradation within the solder.
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  • Kunihiro Noguchi, Y\\={u}ya Endou, Isao Shimizu, Yasuhide Ohno
    2005 Volume 46 Issue 11 Pages 2372-2379
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    Shear strength of Sn–0.39 mass%–3.9 mass%Ag–0.5 mass%Cu lead free solder joint interface on non-resist pure Cu pad were measured to evaluate the true joint strength. Shear test was carried out under the shear speed, Vs=0.14 mm/s and the shear height, Z=0 μm from the non-resist substrate surface. Shear fracture generated and propagated complicatedly on the joint interface. The shear strength using the non-resist pure Cu pad was lower than that using the FR-4 print board. The reaction layer was composed of Cu5.6Sn and Cu6Sn5 intermetallic compound with column shape on the joint interface. Reaction layer thickness, t, column space, s and column width, w have been investigated to analyze the layer structure morphology. Silver composition in the solder influenced on shear strength but not on reaction layer structure morphology. Shear crack propagated intricately in the solder side and the reaction layer side. Shear fracture had the ductile deformation area of the solder and the brittle fracture area of the intermetallic compound.
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  • Seishi Kumamoto, Hitoshi Sakurai, Kazuki Ikeda, Katsuaki Suganuma
    2005 Volume 46 Issue 11 Pages 2380-2385
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    The critical issue for soldering on electroless Ni–Au surface finishes is fragile solder joints. Previous studies have indicated that these weak joints are a result of the formation of a P-rich layer at the joint interface. In this study, the new flux, which contains a Cu compound, demonstrates improved solder joint strength for solder ball attachment on electroless Ni–Au surface finishes. Cross-sectional analysis revealed that this new flux gives a thinner P-rich layer at the joint interface than that seen with a conventional flux. Moreover, the formation of a uniformly thin Cu–Sn intermetallic layer on the Ni–P plated surface is observed after reflow soldering. We conclude that this Cu–Sn layer formation during reflow impedes extra diffusion of Ni into solder from the plating surface so that the growth of a P-rich layer can be effectively inhibited and, thus, the joint strength is improved.
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  • Jeong-Won Yoon, Hyun-Suk Chun, Seung-Boo Jung
    2005 Volume 46 Issue 11 Pages 2386-2393
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    The interfacial reactions and joint reliabilities between Sn–9 mass%Zn solder and an electroless nickel-immersion gold (ENIG) plated Cu substrate were investigated during reflow and isothermal aging at temperatures between 343 and 423 K for aging times of up to 2400 h. After reflowing and aging, the intermetallic compound (IMC) formed at the interface was found to be AuZn3. No Ni-containing reaction products, such as Ni–Zn, Ni–Sn and Ni3P, were observed to form at the interface. The interfacial microstructure and shear strength remained nearly unchanged, irrespective of the reflow time, and the fractures occurred in the solder matrix. In the ball shear tests conducted after aging treatment, the shear strength of the samples decreased during the initial 100 h of aging and then remained constant with prolonged aging. The interfacial reaction between the Sn–Zn solder and the Ni–P plating layer was found to be suppressed by the formation of a layer-type Au–Zn IMC layer, resulting in the desirable interfacial reaction. Compared to the fast interfacial reaction between the Sn–9Zn solder and Cu substrate, the Sn–9Zn/ENIG solder joint was considered to have a superior joint reliability.
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  • Hiroshi Nishikawa, Akira Komatsu, Tadashi Takemoto
    2005 Volume 46 Issue 11 Pages 2394-2399
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    In order to clarify the effect of the addition of Co to Sn–Ag solder on the interfacial reaction between solder and metals, the reaction between solder and metals, such as plated Fe and Cu, has been investigated. Sn–3.5 mass%Ag–xCo solders (x=0, 0.1, 0.3, 0.5 and 1.0 mass%) was specially prepared in this study. A reaction test between the solders and plated iron was performed at 723 K for 32.4 ks by using an oven in a normal air to mainly investigate the effect of the addition of Co to solder on the dissolution thickness of plated iron. And then a reaction test between solder and a Cu substrate was carried out to investigate the effect of the addition of Co to solder on the wettability of solder and the formation of intermetallic compound at the interface. For the reflow process, specimens were heated in a radiation furnace at 523 K for 60 s and, for the aging process, some specimens were heat-treated in an oil bath at 423 K for 168 h and 504 h. As a result of the reaction test between the solder and plated iron, it was found that the addition of Co to Sn–3.5Ag solder was certainly effective to reduce the dissolution thickness of plated iron. Then as a result of the reaction test using Cu substrate, it was clear that there was little effect of the addition of Co on the wettability of solder and Sn–3.5Ag solder added minor Co was certainly effective to reduce the growth rate of the intermetallic compound at the aging process.
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  • Sung Soo Kim, Jong Hoon Kim, Seong Woon Booh, Tae-Gyu Kim, Hyuck Mo Le ...
    2005 Volume 46 Issue 11 Pages 2400-2405
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    The soldering behaviour of the eutectic Au–Sn alloy on two kinds of under bump metallurgy was studied in relation to time and temperature. For a Ni substrate, two types of the intermetallic compounds were observed at the joint: (Au,Ni)3Sn2 and (Au,Ni)3Sn. As the soldering temperature increased, the shape of the (Au,Ni)3Sn2 grains generally changed from a long, thin rod-type to a short, thick type. The degree of buildup of the interfacial intermetallic compounds was similar up to 32 min, even if the soldering was conducted at three different temperatures between 300°C and 400°C. In addition, the reaction of the eutectic Au–Sn solder with the sputtered under bump metallurgy (Al/Ni(V)/Au) was studied at 300°C. By 20 s of soldering, the protective Au layer was dissolved away and the Ni(V) layer started to dissolve into the solder. Thus, some of the Au reacted with the Al underlayer to form the Au8Al3 phase, which was accompanied by volume expansion at the joint. The (Au,Ni)3Sn2 layer was then lifted up, and several interlocked (Au,Ni)3Sn2 grains were broken and separated at weak points along the joint interface. In this way, the joint interface was separated from the Si chip, and a resultant failure occurred in the device.
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  • Takashi Yamamoto, Shigeaki Sakatani, Shinji Kobayashi, Keisuke Uenishi ...
    2005 Volume 46 Issue 11 Pages 2406-2412
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    For the formation of micro joint not to melt by secondary reflow soldering, we tried to enhance the reactivity of Sn–Ag solder with Au/Ni–20Co plating. It was confirmed that the addition of Co in Ni and existence of Au plating effectively accelerated the reaction and the Sn–Ag solder completely transformed to the intermetallic compounds with a higher melting temperature.
    Particularly, the addition of Co in Ni changed the interfacial reaction layer from Ni3Sn4 to (Ni,Co)Sn2 with higher diffusivity of Ni which enhanced the formation of the intermetallic phases. This process is expected to replace the packaging technology using high temperature solders.
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  • Jae-Ean Lee, Keun-Soo Kim, Katsuaki Suganuma, Junichi Takenaka, Koichi ...
    2005 Volume 46 Issue 11 Pages 2413-2418
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    The potentials of the newly designed Zn–xSn (x=40, 30, and 20 mass%) alloys as high temperature lead-free solders and their interface properties on Cu substrate were investigated, focusing on the interface microstructure and mechanical properties. Hypereutecic alloys show two endothermic peaks in differential scanning calorimetry (DSC), one appears at 200°C and the other varies from 365 to 383°C with decreasing Sn content. These peaks are well associated with the eutectic and liquidus temperatures of binary Zn–Sn alloys, and little undercooling were observed on cooling. Two Cu–Zn compound layers are formed at the Zn–Sn alloys/Cu interface. The reaction phases are identified as γ-Cu5Zn8 and ε-CuZn5 phases from the Cu side, and no Cu–Sn compound was identified. The thickness of the reaction layers and the joining strength increased with decreasing Sn content. Each joint shows a different fracture pattern, which gradually changes from transgranular in Zn–Sn alloys near the interface to the at ε-CuZn5/γ-Cu5Zn8 reaction layers with decreasing Sn content.
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  • Kazuhiro Nogita, Jonathan Read, Tetsuro Nishimura, Keith Sweatman, Sho ...
    2005 Volume 46 Issue 11 Pages 2419-2425
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    Soldering alloys based on the Sn–Cu alloy system are amongst the most favourable lead-free alternatives due to a range of attractive properties. Trace additions of Ni have been found to significantly improve the soldering characteristics of these alloys (reduced bridging etc.). This paper examines the mechanisms underlying the improvement in soldering properties of Sn–0.7 mass%Cu eutectic alloys modified with concentrations of Ni ranging from 0 to 1000 ppm. The alloys were investigated by thermal analysis during solidification, as well as optical/SEM microanalyses of fully solidified samples and samples quenched during solidification. It is concluded that Ni additions dramatically alter the nucleation patterns and solidification behaviour of the Sn–Cu6Sn5 eutectic and that these changes are related to the superior soldering characteristics of the Ni-modified Sn–0.7 mass%Cu alloys.
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  • Chen-nan Chiu, Yu-chih Huang, An-ren Zi, Sinn-wen Chen
    2005 Volume 46 Issue 11 Pages 2426-2430
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    Isoplethal sections of the 250°C phase equilibria at 95 at%Sn and 97 at%Sn and that of the liquidus projection at 97 at%Sn of the Sn–Ag–Cu–Ni system were determined. Sn–Ag–Cu–Ni quaternary alloys at constant Sn contents were prepared. The alloys for the isothermal phase relationship determination were equilibrated at 250°C for various lengths of time, and then the equilibrium phases in the annealed alloys were analyzed. The alloys for the liquidus projection determination were melted at 1000°C, and were solidified in the furnace at a cooling rate approximately 10°C/min. The solidified alloys were metallographically examined and the primary solidification phases were determined. The isoplethal sections of the 250°C phase equilibria and the liquidus projection were constructed based on the quaternary experimental data and the 250°C isothermal sections and the liquidus projection of the constituent ternary systems, respectively. Neither ternary nor quaternary intermetallic compounds were found. Most of the binary compounds have significant ternary solubilities, but only very limited quaternary solubilities. Four different primary solidification phases are found of the Sn–Ag–Cu–Ni alloys with 97 at%Sn, and the compositional regime of the primary Ni3Sn2 phase is relatively much smaller.
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  • Ying-Hui Wang, Matiar R Howlader, Kenji Nishida, Takashi Kimura, Tadat ...
    2005 Volume 46 Issue 11 Pages 2431-2436
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    A method for room temperature bonding of lead-free solders in different environments (vacuum, N2, air) was developed to avoid the problems caused by the high melting temperature of lead-free alloys. The method is called as surface activated bonding (SAB) method. In order to understand the influence of oxidation of Sn–Ag alloy on the bonding characteristics, the surface oxides were removed by argon fast atom beam (Ar-FAB) irradiation and then the growth of the oxides on the alloy surfaces in air was investigated by using X-ray photoelectron spectroscopy (XPS). The oxidation of Sn–Ag alloy appeared a logarithm law at room temperature. The information gathered in the investigation was applied to flip chip bonding, using Sn–Ag–Cu solder bumps at room temperature. The bond strength in different bonding environments was compared, and the results showed that the bond strength depended on the oxide thickness, and by controlling the oxidation process, a room temperature bonding might be possible even in non-vacuum conditions.
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  • Masahiro Kubota
    2005 Volume 46 Issue 11 Pages 2437-2442
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    The structure and morphology of coarse-scale globular and smaller spheroidal particles in an isothermally aged Al–10Mg–0.5Ag (mass%) alloy have been charcterised by means of transmission electron microscopy. Coarse-scale globular and smaller spheroidal particles were commonly observed in an over-aged sample aged for 72 h at 240°C. The coarse-scale globular and smaller spheroidal particles were identified by electron microdiffraction to have the face-centered cubic structure of equilibrium β phase (Al3Mg2) (lattice parameter a=2.824 nm). The orientation relationship between the β phase and α-Al matrix was such that: (100)β||(100)α and [001]β||[001]α. This orientation relationship differs from those reported previously for the β phase formed in binary Al–Mg alloys. The coarse-scale globular β particles had invariably internal faulted structures.
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  • Masao Hayakawa, Saburo Matsuoka, Yoshiyuki Furuya, Yoshinori Ono
    2005 Volume 46 Issue 11 Pages 2443-2448
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    A new observation method was developed for visualizing microstructure on a chemical mechanically polished (CMP) surface for tempered martensite of JIS-SCM440, a medium-carbon steel.
    The CMP and an electropolished (EP) surfaces were observed using an atomic force microscope (AFM) and a field emission type-scanning electron microscope (FE-SEM), respectively. AFM images, FE-secondary and backscattered electron images and electron backscattered patterns (EBSP) were obtained for the CMP and EP surfaces.
    The AFM and FE-secondary electron images of the EP surface clearly visualized martensite blocks and cementite particles, since unevenness corresponding to blocks and cementite particles was created by electropolishing.
    On the other hand, the AFM images of the CMP surface revealed that the CMP process produced a very smooth surface with unevenness not exceeding 10 nm. The FE-backscattered electron images of the CMP surface only visualized the crystal misorientation of the martensite matrix microstructure, since the images are not influenced by surface unevenness.
    The CMP surface is more appropriate than the EP surface for EBSP measurements, since the CMP surface is smoother than that of the EP surface. Blocks with a high-angle boundary exceeding 15° could be recognized by EBSP mapping, but laths with a low-angle boundary below 3° could not.
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  • Atsunori Kamegawa, Takao Funayama, Junya Takahashi, Hitoshi Takamura, ...
    2005 Volume 46 Issue 11 Pages 2449-2453
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    The present paper describes the grain size refinements of an Al–7.8 mass%Mg alloy by hydrogen heat-treatment of so-called Hydrogenation–Disproportionation–Desorption–Recombination (HDDR) process. Upon hydrogenation of the alloys, a disproportionation reaction occurred in forming of MgH2 embedded in Al matrix phases. In the subsequent hydrogen-desorption of the alloys, MgH2 was decomposed and was resolved into Al matrix phase, in resulting in the original solid solution of the alloys. This means that the HDDR phenomena take place in the Al–7.8 mass%Mg alloy. It is rather surprising that the grain size of the alloy turned into a several 10 nm after HDDR treatments such as heat-treatment at 350°C under hydrogen pressure of 7.5 MPa for 72 h, in following by the hydrogen desorption treatment at 350°C for 4 h in vacuum. This could be the first report that HDDR treatments are effective in producing the fine grain size of the order of nm in Al-based alloys.
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  • S. V. S. Narayana Murty, Shiro Torizuka, Kotobu Nagai
    2005 Volume 46 Issue 11 Pages 2454-2460
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    During large strain deformation of materials, the high angle grain boundary spacing tends to approach the order of mean thermal diffusion distances for given deformation conditions. Based on the results of microstructural and grain size analysis in low carbon steel subjected to large strain-high Z deformation, the evolved ferrite grain size was found to be controlled by the Zener-Hollomon parameter and grain boundary diffusion was found to be the controlling mechanism.
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  • Tomoya Goda, Manabu Iguchi, Yasushi Sasaki, Hiromichi Kiuchi
    2005 Volume 46 Issue 11 Pages 2461-2466
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    Bubble formation from a downward-facing single-hole nozzle immersed in a still circular water bath has been observed with a high-speed video. An empirical equation is derived for the frequency of bubble formation, fB0, as a function of gas flow rate Qg, the inner and outer diameters of the nozzle, dni and dno, the acceleration due to gravity, g, and the physical properties of fluids. A cross-flow is imposed on the nozzle by rotating the bath around its vertical axis. The frequency of bubble formation in the presence of the rotating flow, fB, is predicted using fB0 and the rotating flow velocity, vθ.
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  • Olga. P. Terleeva, Young-Joo Oh, Myoung-Ryul Ok, Vladimir V. Utkin, He ...
    2005 Volume 46 Issue 11 Pages 2467-2472
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    The coating characteristics on the surfaces of the aluminum alloys A1230, A2017, Al–7.6 mass%Si, and Al–10.4 mass%Si formed at AC polarization were investigated. The intervals of current densities and process durations were checked, and data consisting of coating thickness and increases in size and weight were obtained. The presence of the high-temperature aluminum oxide phases, which provide high physical-mechanical coating characteristics, was registered with the help of the Bruker D8 Advanced X-ray diffractometer.
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  • Fumitaka Otsubo, Katsuhiko Kishitake, Toshio Terasaki
    2005 Volume 46 Issue 11 Pages 2473-2477
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    The self-fluxing alloy was thermal sprayed by using combustion flame spraying (FS) and high energy plasma spraying (HPS) as well as high velocity oxy-fuel spraying (HVOF) processes under different combustion chamber pressures of 0.56, 0.70 and 0.84 MPa. As-sprayed HVOF (0.56 MPa) coating contained a large amount of non-melted particles. Whereas, the as-sprayed HVOF (0.70 MPa) and (0.84 MPa) coatings were composed of melted and non-melted particles similar to the FS and HPS coatings. The compressive residual stress distributed through-thickness in the as-sprayed HVOF (0.56 MPa) coating. On the other hand, the tensile residual stress distributed through-thickness in the HVOF (0.70 MPa) and (0.84 MPa) coatings as well as the FS and HPS coatings. However, the through-thickness residual stress distribution of the HVOF coatings exhibited a low value under 100 MPa in the whole area of coating.
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  • Nader El-Bagoury, Toru Matsuba, Kaoru Yamamoto, Hirofumi Miyahara, Kei ...
    2005 Volume 46 Issue 11 Pages 2478-2483
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    The influences of solution and homogenization heat treatments and grain size on the microstructure and mechanical properties of cast Inconel 718 alloy have been investigated. The microstructure of as cast In718 alloy consists of primary γ, eutectic (γ+NbC) and eutectic (γ+Ni2Nb). Fine and coarse grain structure specimens were achieved by controlling casting temperature. The fine grain specimen has a higher volume fraction of Ni2Nb, 4.99%, than the coarse grain one, 3.45%. The volume fraction of NbC is 1.0 to 1.3% in both fine and coarse grain specimens, and almost unchanged by solution heat treatment. In case of the fine grain specimen, the as cast volume fraction of Ni2Nb decreases by solution treatment to 1.26% at the temperature of 1403 K for 0.5 h holding time and completely dissolute after 4 h at the same temperature. By increasing temperature to 1440 K, it takes only 2 h to vanish Ni2Nb from the microstructure. The coarse grain structure gives lower tensile strength for both as cast and as solution treated in compare with fine grain ones. The volume fraction of Ni2Nb phase has a significant influence on the tensile strength and strain values, while it has no effect on the yield stress and hardness measurements. The fracture crack during tensile test is selectively initiated at Ni2Nb phase and propagated along it in interdendritic zone.
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  • Satoru Kanai, Sachio Seto, Hiroyuki Sugiura
    2005 Volume 46 Issue 11 Pages 2484-2489
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    To investigate the feasibility of joining the TiAl intermetallic compound to titanium alloys, the diffusion bonding of TiAl to Ti–17 alloys (Ti–Al–Cr–Mo–Sn–Zr, near β-phase alloy) was performed, and the effects of joining parameters on the joint strength and the diffusion phase at the bonding interface were examined.
    The major results are as follows:
    For diffusion bonding of TiAl to Ti–17, joints which fractured at the TiAl base metal on the tensile test were obtained in case where the thickness of the diffusion phase at the bonding interface exceeded 10 μm. The observation of the diffusion phase revealed that a solid solution of TiAl matrix containing the alloying elements of Ti–17 such as Cr, Mo, Zr and Sn, and a small amount of Ti3Al particles were formed, while no lamellar Ti3Al detrimental to the joint strength was detected. This result can be interpreted by taking into account the effects of Cr and Mo on the Ti–Al phase diagram. The bonding temperature to give the maximum tensile strength of the TiAl to Ti–17 joint was found to be higher than those of TiAl to pure titanium joint and TiAl to Ti–6Al–4V alloy joint.
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  • Sosoon Park, Shigeo Kitsukawa, Kenji Katoh, Sigenori Yuyama, Hiroaki M ...
    2005 Volume 46 Issue 11 Pages 2490-2496
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    In Service Inspection by Acoustic Emission technique offers the user significant advantages, such as the capability of monitoring corrosion damage of the bottom plates of an oil tank without opening it. In this study, the mechanism of AE generation due to the corrosion of tank bottoms on strong acidic sand was examined. During the corrosion process, the corrosion rate and the AE activity were estimated and the relation between these two factors was examined. The sources of AE due to the corrosion of tank bottoms on an acidic soil were specified. Here, the physical foundations of a global diagnosis technique based on the AE method for evaluating the corrosion damage to tank bottoms were presented.
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  • Yoshiaki Mizukami, Kozo Osakada
    2005 Volume 46 Issue 11 Pages 2497-2503
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    Layered compaction manufacturing (LCM), which is a hybrid process of powder compaction and milling in layers, is applied to the fabrication of a cemented carbide mold (WC–9 mass%Co) for the forming of optical glass lenses with internal cooling channels, which are placed along the molding cavity. The mold is produced by repeating the process of powder compaction with the subsequent creation of grooves filled with paraffin wax as a sacrificial material. The channels placed along the molding cavity are formed during the sintering process by dewaxing. In the sintering process, the extent of deformation in the shape of the internal channels and molding cavity is measured. It is found that the shapes of the channels and cavity exhibit uniform linear shrinkage in the range from 17 to 19%. By filling the molding cavity with epoxy resin, the cooling capability of the mold by air is investigated by performing experiments as well as two-dimensional finite differences simulation. The cooling effect of the mold in the glass lens-forming process is also estimated by the simulation. For both resin and glass, when air is supplied to the channels, the obtained cooling rate is approximately ten times higher as compared to natural cooling at an ambient temperature.
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  • Wen-Jun Li, Rong Tu, Takashi Goto
    2005 Volume 46 Issue 11 Pages 2504-2508
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    TiB2–SiC system composites were prepared using TiB2 and SiC powders as starting materials by an arc-melted method in Ar atmosphere. The TiB2–SiC system was binary eutectic. The eutectic composition was 40TiB2–60SiC (mol%) showing a labyrinth texture. The hardness of the eutectic composite was 27 to 30 GPa at the loads from 0.98 to 9.8 N. The electrical conductivity of the composites increased with increasing the content of TiB2. The electrical conductivity of the eutectic composite slightly decreased from 6.5 to 6.1×105 Sm−1 with increasing temperature from 298 to 1200 K. The thermal conductivity of the composites increased with increasing the content of SiC. The thermal conductivity of the eutectic composite decreased from 70 to 45 WK−1 m−1 with increasing temperature.
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  • Daesup Kil, Yongjae Suh, Heedong Jang, Jaechen Lee, Changbin Song, Won ...
    2005 Volume 46 Issue 11 Pages 2509-2513
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    Nanosize powder of ZrVFe alloy has been prepared by a laser ablation method using a ZrVFe alloy as a target material. Ablation of the target alloy was carried out in a liquid container. The laser fluence, energy density at the target surface, was adjusted by manipulating the laser power and focus size to control the ablating conditions. The obtained colloidal dispersions of the nanoparticle were filtered and dried for characterization. The crystal structure of prepared nanoparticles maintained clear crystallinity and was the same as that of the original target alloy by comparison of the X-ray diffraction pattern. The particle sizes were distributed at around 100 nm depending on the used ablation conditions. The minimum average particle size of 71 nm was obtained at the laser fluence of 20.3 J/cm2, while the average size was not proportional to the laser fluence. The morphologies and oxidation state of the particle have been discussed for possible use of the ZrVFe powder as a getter material.
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  • Jun Akiyama, Masami Hashimoto, Hiroaki Takadama, Fukue Nagata, Yoshiyu ...
    2005 Volume 46 Issue 11 Pages 2514-2517
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    Orientation of hydroxyapatite (HAp) crystals is one of the promising ways to utilize their anisotropic nature of chemical and biological properties. On the other hand, the development of super conducting magnet technology enables to introduce a high magnetic field which can control crystal orientation of non-magnetic materials with magnetic anisotropy. In this study, a horizontal 10 T static magnetic field was imposed on slurry containing HAp crystals under the horizontal mold rotation during slip casting process so as to introduce c-axis orientation for some amount of crystals in the sample, and then it was sintered in atmosphere without the magnetic field. From SEM observation and X-ray diffraction, it has been found that the c-axis of pillar shape HAp crystals in the sample treated with the magnetic field and the mold rotation were oriented to a particular direction and it was enhanced by the subsequent sintering process, while the c-axis crystal orientation of the sample treated without the magnetic field and with the mold rotation was not observed before and after the sintering.
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  • Yoshinori Morisaki, Hiroshi Araki, Hiroyuki Kitagawa, Masaki Orihashi, ...
    2005 Volume 46 Issue 11 Pages 2518-2524
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    Plastic deformation study of Bi2Te3-related materials was performed. The ingots were grown by the Bridgman method using source materials with nominal compositions of Bi0.5Sb1.5Te3, Bi2Sb2.85Se0.15 and Bi1.8Sb0.2Te2.85Se0.15. Disks were cut from the ingots, and were then deformed by either cold-pressing or by hot-pressing under pulse current heating. The crystal structures of the deformed samples were identified by X-ray diffraction. All diffraction peaks were assigned to the Bi2Te3 structure, and the diffraction patterns indicate that the surfaces and bottoms of the samples were highly oriented in the hexagonal (00-l) plane. Hall effect measurements show the carrier concentration of the samples to be at an order of magnitude of 1025 m−3 at room temperature. The power factor for the samples after hot-press deformation exceeded that for the original ingots. The results suggest that hot-press deformation enhances the thermoelectric properties of Bi2Te3-related materials.
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  • Yuma Horio, Hiroyuki Yamashita, Takahiro Hayashi
    2005 Volume 46 Issue 11 Pages 2525-2529
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    N-type Bi1.9Sb0.1Te2.6Se0.4 alloys were prepared by a rapid solidification technique and subsequent hot-pressing method. The microstructure and thermoelectric properties of the alloys were investigated as a function of the hot-pressing temperature and pressure. The X-ray diffraction measurements indicate that the grains are preferably aligned with the c-axis perpendicular to the direction of the hot-pressing force by the hot-pressing. Hot-pressing at higher temperature promotes the grain growth in the alloys. The Seebeck coefficient (α) and electrical resistivity (ρ) decrease with an increase in the hot-pressing temperature, whereas the thermal conductivity (κ) increases. The specimens prepared at higher temperature greater than 733 K show better thermoelectric performance: the largest dimensionless figure of merit (ZT) is 1.08 at room temperature.
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  • Hao-Long Chen, Yang-Ming Lu, Jun-Yi Wu, Weng-Sing Hwang
    2005 Volume 46 Issue 11 Pages 2530-2535
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    Nickel oxide (NiO) films with NaCl-type structure were deposited onto Corning glass substrates at different substrate temperatures by radio-frequency (RF) magnetron sputtering under an RF power of 200 W. The resulting films were analyzed by grazing-incidence X-ray diffraction, ultrahigh resolution scanning electron microscopy (HR-SEM) and high-resolution transmission electron microscopy (HR-TEM). The relationships among the gas ratio of O2, substrate temperature, preferred orientation and microstructure of the NiO films were investigated. Those films deposited at a substrate temperatures of 303 or 473 K with the ratio of oxygen varying from 0 to 100% displayed a (111) preferred orientation. At the substrate temperature of 673 K, while the (111)-orientated film was obtained under a low ratio of oxygen (<50% O2), a (200) preferred orientation was developed under 100% oxygen. All the films have a columnar structure with the growth direction perpendicular to the surface. The origin of the preferred orientations is also discussed.
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  • Shi-Wei Chen, Chun-Hao Koo, Hsin-Erh Huang, Chia-Hua Chen
    2005 Volume 46 Issue 11 Pages 2536-2540
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    This study investigates the characteristics of IMI (ITO–Metal–ITO) transparent conductive thin films, with an Ag–Ti alloy intermediate layer. Multi-layers were deposited by sputtering. ITO–AgTi–ITO films have better transmittance than ITO–Ag–ITO films in the visible wavelength range. The maximum transparency is 94% after being annealed at 573 K in a vacuum. Although the resistivity of ITO–AgTi–ITO films is slightly higher than that of ITO–Ag–ITO films, the former apparently exhibit greater thermal stability and durability. After exposure to the environment at 323 K with a relative humidity of 90% for 144 h, corrosive spots appear on ITO–Ag–ITO films but not on ITO–AgTi–ITO films.
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  • Zan Bian, Akihisa Inoue
    2005 Volume 46 Issue 11 Pages 2541-2544
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    New Ce–Cu–Fe–Al–Si bulk metallic glasses (BMGs) with high glass formation ability (GFA) and large supercooled liquid regions (ΔTx, ΔTx=TxTg) were developed. Investigation shows that the addition of Fe and Si elements is very effective to improve the glass formation ability of Ce-based BMGs. For an optimizing composition, the ΔTx value is 95 K and the alloy can be prepared into bulk metallic glass rods with the diameters of at least 10 mm. In the Ce–Cu–Al–Fe alloys, the glass transition temperature (Tg), crystallization temperature (Tx) and ΔTx increase with increasing Fe content. The reduced glass transition temperature (Trg=TgTl) of the present BMG system is about 0.5–0.6 and is much lower than that of other metal base BMG systems with high GFA. Compressive fracture strength (σf) and Young’s modulus (E) of the Ce–Cu–Al–Fe BMGs are ∼930 MPa and ∼45 GPa, respectively, and increase with increasing Fe content.
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  • Hua Men, Tao Zhang
    2005 Volume 46 Issue 11 Pages 2545-2547
    Published: 2005
    Released: November 15, 2005
    JOURNALS FREE ACCESS
    (Cu0.5Zr0.425Ti0.075)99Sn1 bulk glassy alloy exhibited a large plastic strain to failure, about 8%, in uniaxial compression. High resolution transmission electron microscopy showed formation of nanocrystallites in the sample subjected to a plastic strain of about 3%. The large plasticity was attributed to the deformation-induced nanocrystalization in an amorphous phase.
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