Browsing by Author "Liang, Y. C."

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Anisotropic grain growth and crack propagation in eutectic microstructure under cyclic temperature annealing in flip-chip SnPb composite solder joints
(2013-07-01)
Liang, Y. C.
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Lin, H. W.
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Chen, H. P.
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Chen, C.
;
Tu, K. N.
The evolution of eutectic structure under temperature cycling tests (TCTs) in SnPb composite solder joints has been investigated. After 500 cycles of TCT, the Sn grains coarsened and developed anisotropic stripes close to the necking site in the solder joint because of stress-induced atomic migration. Then, cracks triggered by thermal stress were observed to propagate along the Sn stripe interfaces. After a prolonged 14,410 cycles of TCT, the cracks expanded across the entire solder joint and led to electrical open failure. (c) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Electromigration in reduced-height solder joints with Cu pillars
(2016-04)
Chen, Ming-Yao
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Liang, Y. C.
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Chen, Chih
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材料科學與工程學系
;
Department of Materials Science and Engineering
This paper investigates the current-enhanced surface diffusion of solder along the side walls of Cu pillars. Two solder joints, Cu pillar/10-A mu m-solder/Ni and Cu pillar/Ni/10-A mu m-solder/Ni, were subjected to a 1.2 x 10(4) /cm(2) current density at 125 A degrees C for various amounts of time. The Sn atoms may diffuse to the Cu pillars side walls and form Cu6Sn5 intermetallic compounds (IMCs). Because the Sn atoms are drawn from the solder joints, serious voids are formed in these joints. Side diffusion is more serious for the Cu pillar/Ni/10-A mu m-solder/Ni joints than the Cu pillar/10-A mu m-solder/Ni joints because, instead of forming Ni3Sn4 IMCs, the Sn atoms prefer diffusing into the Cu side walls to form Cu6Sn5 IMCs. This Sn side diffusion accelerates the depletion of solder in the joints and thus may be a serious reliability issue for solder joints with a reduced solder height.
Influence of Cu column under-bump-metallizations on current crowding and Joule heating effects of electromigration in flip-chip solder joints
(2012-02-15)
Liang, Y. C.
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Tsao, W. A.
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Chen, Chih
;
Yao, Da-Jeng
;
Huang, Annie T.
The electromigration behavior of SnAg solder bumps with and without Cu column under-bump-metallizations (UBMs) has been investigated under a current density of 2.16 x 10(4) A/cm(2) at 150 degrees C. Different failure modes were observed for the two types of samples. In those without Cu column UBMs, when SnAg solder bumps that had implemented 2 mu m Ni UBMs were current stressed at 2.16 x 10(4) A/cm(2), open failure occurred in the bump that had an electron flow direction from the chip side to the substrate side. However, in those with Cu column UBMs, cracks formed along the interface of Cu6Sn5 intermetallic compounds and the solder on the substrate side in the Sn-3.0Ag-0.5Cu solder bump that had an electron flow direction from the substrate side to the chip side. A three-dimensional simulation of the current density distribution was performed in order to obtain a better understanding of the current crowding behavior in solder bumps. The current crowding effect was found to account for the void formation on both the chip and the substrate side for the two kinds of solder bumps. One more important finding, as confirmed by infrared microscopy, is that the alleviation of current crowding by Cu column UBMs also helped decrease the Joule heating effect in solder bumps during current stressing. Therefore, the measured failure time for the solder joints with Cu column UBMs appears to be much longer than that of the ones with the 2 mu m Ni UBMs. (C) 2012 American Institute of Physics. [doi:10.1063/1.3682484]
Pressure dependence of the electronic structure and spin state in Fe(1.01)Se superconductors probed by x-ray absorption and x-ray emission spectroscopy
(2011-09-09)
Chen, J. M.
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Haw, S. C.
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Lee, J. M.
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Chou, T. L.
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Chen, S. A.
Pressure dependence of electronic structures and spin states of iron-chalcogenide Fe(1.01)Se superconductors up to similar to 66 GPa has been investigated with x-ray emission spectra and x-ray absorption spectra with partial-fluorescence yield. The intensity of the pre-edge peak at energy of similar to 7112.7 eV of the Fe K-edge x-ray absorption spectrum of Fe1.01Se decreases progressively with pressure up to similar to 10 GPa. A new prepeak at energy of similar to 7113.7 eV develops for pressure above similar to 13 GPa, indicating formation of a new phase. The experimental and the calculated Fe K-edge absorption spectra of Fe(1.01)Se using the FDMNES code agree satisfactorily. The larger compression accompanied by significant distortion around the Fe atoms along the c axis in Fe(1.01)Se upon applying pressure suppresses the Fe 3d-Se 4p and Fe 4p-Se 4d hybridization. The applied pressure suppresses the nearest-neighbor ferromagnetic superexchange interaction and enhances spin fluctuations on the Fe sites in Fe(1.01)Se. A discontinuous variation of the integrated absolute difference values of the K beta emission line was observed, originating from a phase transition of Fe(1.01)Se for a pressure >12 GPa. Fe(1.01)Se shows a small net magnetic moment of Fe(2 broken vertical bar) at ambient pressure, probably arising from strong Fe-Fe spin fluctuations. The satellite line K beta' was reduced in intensity upon applying pressure and became absent for pressure >52 GPa, indicating a continuous reduction of the spin moment of Fe in Fe(1.01)Se superconductors. The experimental results provide insight into the spin state of Fe(1.01)Se superconductors under pressure.
Pressure dependence of the electronic structure and spin state in Fe1.01Se superconductors probed by x-ray absorption and x-ray emission spectroscopy
(2011-09-09)
Chen, J. M.
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Haw, S. C.
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Lee, J. M.
;
Chou, T. L.
;
Chen, S. A.
Pressure dependence of electronic structures and spin states of iron-chalcogenide Fe1.01Se superconductors up to similar to 66 GPa has been investigated with x-ray emission spectra and x-ray absorption spectra with partial-fluorescence yield. The intensity of the pre-edge peak at energy of similar to 7112.7 eV of the Fe K-edge x-ray absorption spectrum of Fe1.01Se decreases progressively with pressure up to similar to 10 GPa. A new prepeak at energy of similar to 7113.7 eV develops for pressure above similar to 13 GPa, indicating formation of a new phase. The experimental and the calculated Fe K-edge absorption spectra of Fe1.01Se using the FDMNES code agree satisfactorily. The larger compression accompanied by significant distortion around the Fe atoms along the c axis in Fe1.01Se upon applying pressure suppresses the Fe 3d-Se 4p and Fe 4p-Se 4d hybridization. The applied pressure suppresses the nearest-neighbor ferromagnetic superexchange interaction and enhances spin fluctuations on the Fe sites in Fe1.01Se. A discontinuous variation of the integrated absolute difference values of the K beta emission line was observed, originating from a phase transition of Fe1.01Se for a pressure >12 GPa. Fe1.01Se shows a small net magnetic moment of Fe-2 broken vertical bar at ambient pressure, probably arising from strong Fe-Fe spin fluctuations. The satellite line K beta' was reduced in intensity upon applying pressure and became absent for pressure >52 GPa, indicating a continuous reduction of the spin moment of Fe in Fe1.01Se superconductors. The experimental results provide insight into the spin state of Fe1.01Se superconductors under pressure.
Pressure-dependent electronic structures in multiferroic DyMnO(3): A combined lifetime-broadening-suppressed x-ray absorption spectroscopy and ab initio electronic structure study
(2010-10-21)
Chen, J. M.
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Lee, J. M.
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Chou, T. L.
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Chen, S. A.
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Huang, S. W.
Variations in the electronic structure and structural distortion in multiferroic DyMnO(3) were probed by synchrotron x-ray diffraction, lifetime-broadening-suppressed x-ray absorption spectroscopy (XAS), and ab initio electronic structure calculations. The refined x-ray diffraction data enabled an observation of a diminished local Jahn-Teller distortion of Mn sites within MnO(6) octahedra in DyMnO(3) on applying the hydrostatic pressure. The intensity of the white line in Mn K-edge x-ray absorption spectra of DyMnO(3) progressively increased with the increasing pressure. With the increasing hydrostatic pressure, the absorption threshold of an Mn K-edge spectra of DyMnO(3) shifted toward a greater energy, whereas the pre-edge line slightly shifted to a smaller energy. We provide the spectral evidence for the pressure-induced bandwidth broadening for manganites. The intensity enhancement of the white line in Mn K-edge spectra is attributed to a diminished Jahn-Teller distortion of MnO(6) octahedra in compressed DyMnO(3). A comparison of the pressure-dependent XAS spectra with the ab initio electronic structure calculations and full calculations of multiple scattering using the code FDMNES shows the satisfactory agreement between experimental and calculated Mn K-edge spectra. (C) 2010 American Institute of Physics. [doi:10.1063/1.3490400]
Pressure-dependent electronic structures in multiferroic DyMnO3: A combined lifetime-broadening-suppressed x-ray absorption spectroscopy and ab initio electronic structure study
(2010-10-21)
Chen, J. M.
;
Lee, J. M.
;
Chou, T. L.
;
Chen, S. A.
;
Huang, S. W.
Variations in the electronic structure and structural distortion in multiferroic DyMnO3 were probed by synchrotron x-ray diffraction, lifetime-broadening-suppressed x-ray absorption spectroscopy (XAS), and ab initio electronic structure calculations. The refined x-ray diffraction data enabled an observation of a diminished local Jahn-Teller distortion of Mn sites within MnO6 octahedra in DyMnO3 on applying the hydrostatic pressure. The intensity of the white line in Mn K-edge x-ray absorption spectra of DyMnO3 progressively increased with the increasing pressure. With the increasing hydrostatic pressure, the absorption threshold of an Mn K-edge spectra of DyMnO3 shifted toward a greater energy, whereas the pre-edge line slightly shifted to a smaller energy. We provide the spectral evidence for the pressure-induced bandwidth broadening for manganites. The intensity enhancement of the white line in Mn K-edge spectra is attributed to a diminished Jahn-Teller distortion of MnO6 octahedra in compressed DyMnO3. A comparison of the pressure-dependent XAS spectra with the ab initio electronic structure calculations and full calculations of multiple scattering using the code FDMNES shows the satisfactory agreement between experimental and calculated Mn K-edge spectra. (C) 2010 American Institute of Physics. [doi:10.1063/1.3490400]
Side Wall Wetting Induced Void Formation due to Small Solder Volume in Microbumps of Ni/SnAg/Ni upon Reflow
(2012)
Liang, Y. C.
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Chen, C.
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Tu, K. N.
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A processing failure of void formation has been observed in 3D IC microbumps due to small solder volume. We prepared the sandwiched Ni/Sn2.3Ag/Ni microbumps with 4 mu m and 11 mu m thick solders and reflowed them at 260 degrees C to study the mechanism of void formation in the processing. Due to the thin solder, intermetallic compound formation of Ni3Sn4 from the two interfaces of the solder joint can physically bridge each other. When that happens, the degree of freedom of motion in the direction normal to the interfaces is removed. Consequently, when the remaining molten solder is drained by side wall reaction, large voids form in the joint. This is a unique mode of processing failure because of the smaller and smaller volume of solder joints in the trend of miniaturization. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.002204ssl] All rights reserved.
Temperature-dependent failure mechanism of SnAg solder joints with Cu metallization after current stressing: Experimentation and analysis
(2013-09-21)
Lin, C. K.
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Tsao, Wei An
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Liang, Y. C.
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Chen, Chih
;
材料科學與工程學系
Temperature-dependent electromigration failure was investigated in solder joints with Cu metallization at 126 degrees C, 136 degrees C, 158 degrees C, 172 degrees C, and 185 degrees C. At 126 degrees C and 136 degrees C, voids formed at the interface of Cu6Sn5 intermetallic compounds and the solder layer. However, at temperature 158 degrees C and above, extensive Cu dissolution and thickening of Cu6Sn5 occurred, and few voids were observed. We proposed a model considering the flux divergency at the interface. At temperatures below 131 degrees C, the electromigration flux leaving the interface is larger than the in-coming flux. Yet, the in-coming Cu electromigration flux surpasses the out-going flux at temperatures above 131 degrees C. This model successfully explains the experimental results. (C) 2013 AIP Publishing LLC.