Browsing by Author "Huang, Annie T."

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Analysis of bump resistance and current distribution of ultra-fine-pitch microbumps
(2013-01-01)
Chang, Y. W.
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Peng, H. Y.
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Yang, R. W.
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Chen, Chih
;
Chang, T. C.
To keep up with the demand of continuous increase in device densities, the integration of three-dimensional integrated circuits (3D-IC) has become the most probable solution, and the utilization of ultra-fine-pitch microbump has emerged as an essential component of 3D-IC technology. In this study, a Kelvin bump structure was fabricated and resistances measured at different angles on a 20.0 mu m microbump were investigated. The microbump resistance at 0 degrees, 60 degrees, 120 degrees, and 180 degrees are 74.7, 45.9, 14.6, and 13.7 m Omega, respectively. These high resistances in microbumps may result in high interconnect resistance and cause resistance/capacitance (RC) delay, and thus lower the electrical performance of 3D-IC. A series of finite-element-model (FEM) was built to analyze the distribution of electric field in microbump. The FEM results have shown that the current is distributed uniformly in the thin solder joint, but current crowding still occurs in the Cu under-bump-metallization (UBM). The finding of the current crowding in the Cu UBM is the main cause of high resistances in the microbump. Thickening the Al trace, for example, from 0.4 mu m to 1.5 mu m, is a direct solution to reduce the unexpected high microbump resistance. A numerical model which treated solder joints as a resistance network was also performed in this study. For comparison, both FEM and the numerical model show the same trend and agree with the measurement results from Kelvin bump structure. The results all point to one thing: thickening the Al trace turn out to be the most effective approach to reduce high microbump resistance. When the Al trace thickness is increased from 0.8 to 3.0 mu m, the microbump resistance is decreased to half of the original value, resulted from the alleviation of current crowding in the Cu UBM. (C) 2012 Elsevier Ltd. All rights reserved.
Electromigration Failure Mechanism in Sn-Cu Solder Alloys with OSP Cu Surface Finish
(2012-09-01)
Chu, Ming-Hui
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Liang, S. W.
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Chen, Chih
;
Huang, Annie T.
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材料科學與工程學系
"Organic solderable preservative (OSP) has been adopted as the Cu substrate surface finish in flip-chip solder joints for many years. In this study, the electromigration behavior of lead-free Sn-Cu solder alloys with thin-film under bump metallization and OSP surface finish was investigated. The results showed that severe damage occurred on the substrate side (cathode side), whereas the damage on the chip side (cathode side) was not severe. The damage on the substrate side included void formation, copper dissolution, and formation of intermetallic compounds (IMCs). The OSP Cu interface on the substrate side became the weakest point in the solder joint even when thin-film metallization was used on the chip side. Three-dimensional simulations were employed to investigate the current density distribution in the area between the OSP Cu surface finish and the solder. The results indicated that the current density was higher along the periphery of the bonding area between the solder and the Cu pad, consistent with the area of IMC and void formation in our experimental results."
Fast phase transformation due to electromigration of 18 mu m microbumps in three-dimensional integrated-circuit integration
(2014-12-15)
Chang, Y. W.
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Chen, Chih
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Chang, T. C.
;
Zhan, C. J.
;
Juang, J. Y.
The electromigration behavior was investigated in 18-mu m SnAg microbumps at 150 degrees C. The monitored resistance increase abruptly soon after the current stressing of 4.6 x 10(4) A/cm(2) was applied but the resistance rose much slower after a certain period of time. The formation of the high-resistivity Ni3Sn4 intermetallic compounds (IMCs) was responsible for the abrupt resistance increase in the beginning of the current stressing. The whole solder joint was transformed into an IMC joint. Because IMC has a higher electromigration resistance than the solder, a much slower increase in resistance was resulted after the solder joint was transformed into IMCs. (C) 2014 Elsevier B.V. All rights reserved.
Hermetic packaging using eutectic SnPb solder and Cr/Ni/Cu metallurgy layer
(2006-11-01)
Huang, Annie T.
;
Chou, Chung-Kuang
;
Chen, Chih
;
材料科學與工程學系
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Department of Materials Science and Engineering
We have developed an easy, low-cost, and low-temperature optoelectronic hermetic packaging technology utilizing the eutectic SnPb solder and the Cr/Ni/Cu bonding pad. Bonding characteristics of the design were investigated in three different setups: silicon-silicon, silicon-glass, and glass-glass samples. Hermeticity was achieved at 200 degrees C without flux for all samples during the final bonding process. The bonding pads did not dewet during or after the reflow process. By utilizing the eutectic SnPb solder, the self-alignment process can be achieved. Because the bonding process was conducted through visual alignment, original misalignment was estimated to be more than 100 mu m. The surface tension of melting solder during the reflow process allowed the samples to self-align and obtain a misalignment of less than 20 mu m after solidification, which was 4% of the entire solder width. The bonding strength of the three setups ranged from 3 to 10 MPa. Among the three setups, glass-glass samples appear to have the strongest bonding strength. This low-temperature and cost-effective soldering process has demonstrated its feasibility and potential utilization in optoelectronic packaging.
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]
Thermomigration of Ti in flip-chip solder joints
(2012-05-01)
Chen, Hsiao-Yun
;
Lin, Han-Wen
;
Liu, Chien-Min
;
Chang, Yuan-Wei
;
Huang, Annie T.
Titanium has a very large heat of transport value of -768 kJ mol(-1). However, thermomigration of Ti in solder joints has not been examined. In this study, void formation was observed in non-current-stressed Al traces during electromigration and thermomigration tests of SnAg solder joints. Voids formed inside the traces located above the solder bumps with no current flow. We found that Ti thermomigration occurred in the joint, resulting in the reaction of Al and Cu, leaving voids behind in the Al trace. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.