The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
C. R. Kao - One of the best experts on this subject based on the ideXlab platform.
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effects of the gold thickness of the Surface fiNish on the interfacial reactions in flip chip solder joints
Journal of Electronic Materials, 2004Co-Authors: Y L Lin, W C Luo, Y H Lin, C. R. KaoAbstract:The effects of Au thickness on the flip-chip solder joints with Cu/Ni/Al underbump metallurgy (UBM) on one end and the Au/Ni Surface fiNish on another was studied. Two different thicknesses, 0.1 µm and 0.65 µm, were used for the Surface fiNish. After assembly, the joints were subjected to thermal aging at 150°C. The difference in Au thickness had a strong effect on the consumption rate of the Ni layer in the UBM as well as on the failure mode of the solder joints. When the Au layer was thin (0.1 µm), the dissolved Cu from the Cu/Ni UBM was able to inhibit the formation of AuSn4. When the Au layer was thick (0.65 µm), the dissolved Cu was not able to inhibit the formation of AuSn4. These AuSn4 enhanced the Ni consumption rate of the UBM. The presence of a large amount of AuSn4 inside the solder also weakened the solder because of the Au embrittlement effect. In view of these observations, the gold thickness on the Au/Ni Surface fiNish must be kept to the miNimum controlled in order to prolong the service life of flip-chip packages.
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reflow soldering and isothermal solid state aging of sn ag eutectic solder on au Ni Surface fiNish
Journal of Electronic Materials, 2001Co-Authors: Chi-wei Liu, Wei-hao Chen, C. R. KaoAbstract:The reaction between the eutectic Sn-3.5Ag solder and the Au/Ni Surface fiNish during reflow as well as during isothermal aging was studied. The Au layer was electroplated and had a thickness of the one μm. The peak reflow temperature was fixed at 250 C while the reflow time was varied between 10 sec and one h. Samples that went through 90 sec reflow time were then subjected to 160 C isothermal aging for up to 875 h. It was found that during reflow the Au layer reacted very quickly with the solder to form AuSn4. One μm of Au layer was consumed in less than 10 sec. As the aging time increased, AuSn4 grains began to separate themselves from the Ni layer at the roots of the grains and started to fall into the solder. When, the reflow time reached 30 sec, all the Au intermetallic head left the interface, and Ni3Sn4 started, to form at the interface. The Ni3Sn4 growth rate followed linear kinetics iNitially (<240 sec), but the growth rate slowed down afterward. During the isothermal aging, only a small amount of (AuxNi1-x)Sn4 resettled back to the interface, and a continuous (Au0.45Ni0.55)Sn4 layer did not form at the interface, unlike the case for the Sn-37Pb solder. This is an important advantage for Sn-3.5 Ag over Sn-37Pb because a continuous (Au0.45Ni0.55)Sn4 layer inevitably will weaken a solder joint. Our observation indicated that many (AuxNi1-x)Sn4 particles were trapped by the Ag3Sn particles, and were hindered from resettling back to the interface.
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Reflow soldering and isothermal solid-state aging of Sn-Ag eutectic solder on Au/Ni Surface fiNish
Journal of Electronic Materials, 2001Co-Authors: Chi-wei Liu, Wei-hao Chen, C. R. KaoAbstract:The reaction between the eutectic Sn-3.5Ag solder and the Au/Ni Surface fiNish during reflow as well as during isothermal aging was studied. The Au layer was electroplated and had a thickness of the one μm. The peak reflow temperature was fixed at 250 C while the reflow time was varied between 10 sec and one h. Samples that went through 90 sec reflow time were then subjected to 160 C isothermal aging for up to 875 h. It was found that during reflow the Au layer reacted very quickly with the solder to form AuSn4. One μm of Au layer was consumed in less than 10 sec. As the aging time increased, AuSn4 grains began to separate themselves from the Ni layer at the roots of the grains and started to fall into the solder. When, the reflow time reached 30 sec, all the Au intermetallic head left the interface, and Ni3Sn4 started, to form at the interface. The Ni3Sn4 growth rate followed linear kinetics iNitially (
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formation and resettlement of au x Ni 1 x sn 4 in solder joints of ball grid array packages with the au Ni Surface fiNish
Journal of Electronic Materials, 2000Co-Authors: R Zheng, G L Luo, A H Lin, C. R. KaoAbstract:The interfacial reactions between eutectic PbSn solder and the solder ball pads with the Au/Ni Surface fiNish were studied. Solder joints subjected to up to three repeated reflow-and-aging treatments were examined. For the reflow, the peak reflow temperature was 225°C, and the reflow time was 115 s. Each aging process was performed at 160°C for 500 h. After the first reflow, all the Au would disappear from the interface, and formed many (AuxNi1−x)Sn4 particles inside the solder joints. The value of x was between 0.99 and 0.75. In addition, there was a thin layer of Ni3Sn4 (1.4 µm) at the interface. After one reflow and one subsequent aging, most of the (AuxNi1−x)Sn4 would relocate from inside the solder joint to the interface, and the value of x for (AuxNi1−x)Sn4 at the interface decreased to 0.45. This (AuxNi1−x)Sn4 resettlement process repeated itself for additional reflow-aging cycles. More reflow-aging treatments, however, made the microstructure of (Au0.45Ni0.55)Sn4 at the interface become more non-planar. It was shown that gravitational effect was not the driving force for the resettlement of (AuxNi1−x)Sn4. It is proposed that the driving force is for (AuxNi1−x)Sn4 to seek Ni at the interface so that it can become more Ni-rich. In other words, the driving force is lowering the Gibbs energy of (AuxNi1−x)Sn4 by dissolving more Ni. A decomposition-diffusion mechaNism is proposed to explain what happened. Kinetic rationales for this rapid resettlement of (AuxNi1−x)Sn4 at such a low temperature were also discussed.
Sufang Wang - One of the best experts on this subject based on the ideXlab platform.
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Water adsorption and dissociation on Ni Surface: Effects of steps, dopants, coverage and self-aggregation
Physical chemistry chemical physics : PCCP, 2013Co-Authors: Yucheng Huang, Chongyi Ling, Tao Zhou, Meng Jin, Sufang WangAbstract:Water–metal interaction has been receiving extensive attention due to its interdisciplinary application. In this paper, on the basis of first-principle calculations and slab models, the behavior of water adsorption and dissociation on planar, stepped and blocked Ni Surfaces is investigated, the effects of steps, Au and Ag dopants, coverage and self-aggregation of water are also disclosed. The results show that: step not only strengthens water–substrate interaction but also facilitates water dissociation. With dopants modification, the adsorption and dissociation properties remain relatively unchanged at lower coverage (1/9 on facets and 1/12 ML on steps) while at higher coverage (1/4 on facets and 1/6 ML on steps) water adsorption is weakened and dissociation activity decreases dramatically. Water adsorption and dissociation properties on Ni Surfaces are essentially unaffected with the increase of coverage. On doped Surfaces, adsorption properties and dissociation activities are closely associated with the ligand effect, which is dependent on the dopant, dopant concentration and Surface morphology. Water self-aggregation enhances water–Surface interaction on all studied Surfaces due to hydrogen bond (network) formation. Furthermore, investigation shows that it does not assist water dissociation.
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Methane dehydrogenation on Au/Ni Surface alloys – a first-principles study
Catalysis Science & Technology, 2013Co-Authors: Yucheng Huang, Chongyi Ling, Tao Zhou, Sufang WangAbstract:We present density-functional theory calculations of the dehydrogenation of CHx (x = 1–4) on Au-alloyed Ni(211) Surfaces, where the Au atoms are substituted on the Ni Surface with the ratio of Au atoms to the total stepped Ni atoms being 1:4, 1:2 and 3:4, respectively. To evaluate the role of Au at the step-edge on the process of methane dehydrogenation, CHx adsorption and dissociation on a pure Ni(211) Surface is also conducted. Our results show that Au addition weakens the adsorbate–substrate interaction. With the increase of the Au concentration, the binding energies of CHx gradually decrease and correlate well with the number of Au atoms on each model. On the Ni(211) Surface, methane experiences a successive dehydrogenation process at the step-edge site in which carbon is eventually formed. As Au is introduced, the relative formation rate of carbon is greatly hampered even with a small amount of Au addition, while an appropriate amount of Au modification on the Ni catalyst has little effect on the activity of the CHx dissociation. Finally, we also demonstrate that the active center for CHx dissociation is dynamic with the variation of the Au concentration.
Chen-han Chou - One of the best experts on this subject based on the ideXlab platform.
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Interfacial reaction between Sn1Ag0.5Cu(Co) solder and Cu substrate with Au/Ni Surface fiNish during reflow reaction
Journal of Alloys and Compounds, 2008Co-Authors: K.s. Lin, Her-yueh Huang, Chen-han ChouAbstract:Abstract In order to clarify the effect of the addition of Co to SAC105 solder, the reaction between solder and Au/Ni Surface fiNish has been investigated, and the joint strength was also evaluated by a ball shear test. After soldering, the interfacial reaction layer in the SAC105 Co solder contained Co, and the chemical composition of intermetallic compounds (IMCs) were identified as (Cu,Ni,Co) 6 Sn 5 and (Ni,Cu,Co) 3 Sn 4 by energy-dispersive X-ray spectrometer (EDX), which sigNificantly differed from that of SAC105 solder. After multiple reflows, the formation rate of the (Cu,Ni,Co) 6 Sn 5 IMC for the Co-added solder slow compared with that of (Cu,Ni) 6 Sn 5 IMC for SAC105 solder. Experimental results clearly indicate that adding small amounts (0.05 wt.%) of Co to SAC105 solder strongly affected the formation of the IMC at the interface. Furthermore, ball shear test results demonstrate that the SAC105 and SAC105 Co solder joints have good joint reliability.
Harumi Yokokawa - One of the best experts on this subject based on the ideXlab platform.
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encroachment of titaNium oxide on Ni Surface for Ni tio2 under reducing atmosphere
Solid State Ionics, 2016Co-Authors: Fangfang Wang, Haruo Kishimoto, Katherine Develosbagarinao, Katsuhiko Yamaji, Teruhisa Horita, Harumi YokokawaAbstract:Abstract The Ni-titaNia (TiO2) system was investigated to understand the phenomenon of titaNia encroachment on Ni Surface as a function of temperature and oxygen partial pressure (PO2) under reducing atmosphere. A network-structured Ni film with widths of about 10 μm was prepared on titaNia. It is found that encroachment of non-stoichiometric TiO2 − x to the Ni Surface occurs when TiO2 is reduced to TiO2 − x with random point defects, as the PO2 is within the range defined by Ni-NiO and TiO2 − x–TinO2n − 1 equilibria. On the other hand, no encroachment to the Ni Surface occurs at much lower PO2, where TiO2 is reduced further to the Magneli phase TinO2n − 1 with ordered shear structure. A possible driving force for TiO2 − x encroachment to the Ni Surface may be attributed to the high Surface energy of TiO2 − x with disordered point defects. Furthermore, these results indicate the possible role of fast Ti diffusion in TiO2 − x which drives its encroachment to the Ni Surface.
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imaging of ch4 decomposition around the Ni ysz interfaces under anodic polarization
Journal of Power Sources, 2005Co-Authors: Teruhisa Horita, Haruo Kishimoto, Katsuhiko Yamaji, Tohru Kato, Yueping Xiong, Natsuko Sakai, Manuel E Brito, Harumi YokokawaAbstract:The catalytic activities of Ni-mesh/YSZ samples for CH4 decomposition and reaction with reformed gases were compared under voltage-applied condition (fuel cell operation condition) by imaging analysis of labeled gases with secondary ion mass spectrometry (SIMS). The effect of applied voltages was compared in the mixture of CH4, D2O, and 18O2 to label the movements of hydrogen and oxygen. A sigNificant carbon deposition was observed at the Ni-mesh under zero-voltage condition. However, the applied voltage formed a thin oxide layer on the Ni Surface and eliminated the deposited carbon on the Ni Surface. Oxygen spill-over around the Ni/YSZ interfaces could effectively eliminate the deposited carbon. A possible reaction mechaNism was considered for the optimum metal–oxide interfaces of SOFCs.
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Imaging of labeled gas movements at the SOFC electrode/electrolyte interfaces
Solid State Ionics, 2004Co-Authors: Teruhisa Horita, Katsuhiko Yamaji, Tohru Kato, Natsuko Sakai, Harumi YokokawaAbstract:Abstract The catalytic activity of metals (Ni and Cu) for CH4 decomposition was compared in the mixture of CH4, D2O (heavy water), and 18O2 (stable isotope of oxygen) by image analysis of secondary ion mass spectrometry (SIMS). Annealing of samples was conducted in the stable isotopes of 18O2 and D2O to label the movements of oxygen and hydrogen at high temperature (1073 K). Mesh-shaped electrode/Y2O3-stabilized ZrO2 samples were adopted to determine the gas/electrode/electrolyte interfaces in a submicrometer level. On the mesh electrode Surfaces (Ni and Cu), thin oxide layers were formed, and the oxide layers were active for isotope oxygen exchange. On the Ni Surface, diffusion of D and/or exchange of H/D occurred within 20 nm in depth. Carbon deposition occurred on the Ni Surface, whereas no carbon deposition was observed on the Cu Surface.
Yucheng Huang - One of the best experts on this subject based on the ideXlab platform.
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Role of Au in Graphene Growth on a Ni Surface
ACS Catalysis, 2014Co-Authors: Yucheng Huang, Chongyi Ling, Tao Zhou, Su Fan Wang, Baoyou GengAbstract:Density functional calculations were performed to investigate the role of Au in graphene growth on the Ni(111) step. It was shown that armchair (AC) and zigzag (ZZ) graphene edge growths have nucleation selectivity, depending on the curvature of the stepped Surface. The AC and ZZ pristine graphene edges are energetically more favorable than the Ni-terminated one, and the stabilities of Au-passivated graphene edges strongly depend on the Au concentration. Au modification on the Ni terrace lowers the energy barrier of C incorporation onto the AC/ZZ graphene edge process, in agreement with the experimental observation that graphene can be produced at the low temperature of ∼723 K with Au alloying. The growth rate of the AC graphene edge is always faster than the ZZ, leading to the ZZ edge’s dominating the circumference of the growing graphene islands. With a decrease in the temperature, the increase in the AC graphene edge growth ratio greatly exceeds that of ZZ, driving the edges to incorporate a zigzag geo...
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Water adsorption and dissociation on Ni Surface: Effects of steps, dopants, coverage and self-aggregation
Physical chemistry chemical physics : PCCP, 2013Co-Authors: Yucheng Huang, Chongyi Ling, Tao Zhou, Meng Jin, Sufang WangAbstract:Water–metal interaction has been receiving extensive attention due to its interdisciplinary application. In this paper, on the basis of first-principle calculations and slab models, the behavior of water adsorption and dissociation on planar, stepped and blocked Ni Surfaces is investigated, the effects of steps, Au and Ag dopants, coverage and self-aggregation of water are also disclosed. The results show that: step not only strengthens water–substrate interaction but also facilitates water dissociation. With dopants modification, the adsorption and dissociation properties remain relatively unchanged at lower coverage (1/9 on facets and 1/12 ML on steps) while at higher coverage (1/4 on facets and 1/6 ML on steps) water adsorption is weakened and dissociation activity decreases dramatically. Water adsorption and dissociation properties on Ni Surfaces are essentially unaffected with the increase of coverage. On doped Surfaces, adsorption properties and dissociation activities are closely associated with the ligand effect, which is dependent on the dopant, dopant concentration and Surface morphology. Water self-aggregation enhances water–Surface interaction on all studied Surfaces due to hydrogen bond (network) formation. Furthermore, investigation shows that it does not assist water dissociation.
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Methane dehydrogenation on Au/Ni Surface alloys – a first-principles study
Catalysis Science & Technology, 2013Co-Authors: Yucheng Huang, Chongyi Ling, Tao Zhou, Sufang WangAbstract:We present density-functional theory calculations of the dehydrogenation of CHx (x = 1–4) on Au-alloyed Ni(211) Surfaces, where the Au atoms are substituted on the Ni Surface with the ratio of Au atoms to the total stepped Ni atoms being 1:4, 1:2 and 3:4, respectively. To evaluate the role of Au at the step-edge on the process of methane dehydrogenation, CHx adsorption and dissociation on a pure Ni(211) Surface is also conducted. Our results show that Au addition weakens the adsorbate–substrate interaction. With the increase of the Au concentration, the binding energies of CHx gradually decrease and correlate well with the number of Au atoms on each model. On the Ni(211) Surface, methane experiences a successive dehydrogenation process at the step-edge site in which carbon is eventually formed. As Au is introduced, the relative formation rate of carbon is greatly hampered even with a small amount of Au addition, while an appropriate amount of Au modification on the Ni catalyst has little effect on the activity of the CHx dissociation. Finally, we also demonstrate that the active center for CHx dissociation is dynamic with the variation of the Au concentration.
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First-principles study toward CO adsorption on Au/Ni Surface alloys.
Chemphyschem : a European journal of chemical physics and physical chemistry, 2012Co-Authors: Yucheng Huang, Tao Zhou, Su Fan WangAbstract:The introduction of a second metal, gold, into a Nickel matrix can effectively improve the catalytic performance and thermal stability of the catalysts toward steam reforming of methane. To investigate the effect of Au on the adsorption properties and electroNic structure of the Ni(111) Surface, we chose CO as a probe molecule and examined CO adsorption on various Au/Ni Surfaces. It was revealed that Au addition weakened the absorbate-substrate interactions on the Ni(111) Surface. With increasing gold concentration, the binding energy declines further. The variation of the binding energies has been interpreted by exploring the electroNic structure of Surface Nickel atoms. The effect of gold can be quantitatively characterized by the slopes of the fitting equations between the binding energy and the number of gold atoms surrounding the adsorption site. Our results show that the binding energy at top sites can be approximately estimated by counting the number of surrounding gold atoms. On one specific Surface, the relative magNitude of the binding energy can be simply judged by the distance between gold and the geometrical center of the adsorption site. This empirical rule holds true for C, H, and O adsorption on the Au/Ni Surface. It may be applicable to a system in which a doped atom of larger atomic size is incorporated into the host metal Surface by forming a Surface alloy.