Browsing by Author "Liang, SW"

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3-D simulation on current density distribution in flip-cbip solder joints with thick CuUBM under current stressing
(2005)
Liang, SW
;
Shao, TL
;
Chen, C
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In flip-chip solder joints, Cu has been used as a under-bump metallization (UBM) for its excellent wettability with solders. In addition, electromigration has become an crucial reliability concerns for fine-pitch flip chip solder joints. In this paper, 3-D finite element method was employed to simulate the current density distribution for the eutectic SnPb solder joints with 5 mu m, 10 mu m, and 20 mu m thick Cu UBM. It was found that the thicker the UBM is, the lower the maximum current density inside the solder. The maximum current density decreased from 4.37 X. 10(4) A/cm(2) to 7.54 x 10(3) A/cm(2) when the thickness of the UBM changed from 5 gm to 20 mu m. Thicker Cu UBM can, effectively relieve the current crowding effect inside the solder.
Effect of Al-trace dimension on Joule heating and current crowding in flip-chip solder joints under accelerated electromigration
(2006-04-24)
Liang, SW
;
Chang, YW
;
Chen, C
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Three-dimensional thermoelectrical simulation was conducted to investigate the influence of Al-trace dimension on Joule heating and current crowding in flip-chip solder joints. It is found that the dimension of the Al-trace effects significantly on the Joule heating, and thus directly determines the mean time to failure (MTTF). Simulated at a stressing current of 0.6 A at 70 degrees C, we estimate that the MTTF of the joints with Al traces in 100 mu m width was 6.1 times longer than that of joints with Al traces in 34 mu m width. Lower current crowding effect and reduced hot-spot temperature are responsible for the improved MTTF. (c) 2006 American Institute of Physics.
Electromigration in eutectic SnPb solder bumps with Ni/Cu UBM
(2005)
Chiu, SH
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Liang, SW
;
Chen, C
;
Lin, SS
;
Chou, CM
This study investigates the electromigration behavior of eutectic SnPb solder bumps with Ni/Cu UBM, in which the thickness of the Ni and Cu layer is 3 pm and 5 pm, respectively. It was found that the SnPb solderjoints have better electromigration resistance than that of SnAg bumps with thin film UBM. The thermal characteristic of SnPb solder joints under current stressing was measured by infrared technique. The Joule heating effect was less serious due to the wide Al trace of 100 mu m. Besides, a three-dimensional simulation on current density distribution was performed to examine the current crowding behavior in the joint. The results show that the current crowding occurs at the entrance point of the Al trace, which caused higher formation rate of intermetallic compounds there, and thus open failure occurred.
Redistribution of Pb-rich phase during electromigration in eutectic SnPb solder stripes
(2006-03-01)
Chou, CK
;
Chen, CA
;
Liang, SW
;
Chen, C
;
材料科學與工程學系
The microstructural evolution occurring within the eutectic SnPb solder during electromigration is investigated utilizing Blech specimens. Solder stripes of about 3 mu m in thickness were fabricated on Cu/Ti metallization. It was found that the Pb-rich phase ripened and aligned along the direction of the electron flow following the current stressing of 9.7x10(3) A/cm(2) at 80 degrees C for 24 h. As the stressing time or current density increased, the redistribution of the Pb-rich phase became more significant. Three-dimensional simulation was performed to examine the change in resistance and current-density distribution during electromigration. It was found that when the Pb-rich phase aligned along the direction of the electron flow, the total resistance of the solder stripe decreased. This reduction in total resistance may provide the driving force for the redistribution of the Pb-rich phase during electromigration. In addition, current crowding occurred in the vicinity of the interface of the Pb-rich and Sn-rich phases, creating a gradient of current density. This gradient might trigger the resistive Pb atoms to align along the direction of the electron flow.
Relieving the current crowding effect in flip-chip solder joints during current stressing
(2006-01-01)
Liang, SW
;
Shao, TL
;
Chen, C
;
Yeh, ECC
;
Tu, KN
Three-dimensional simulations for relieving the current crowding effect in solder joints under current stressing were carried out using the finite element method. Three possible approaches were examined in this study, including varying the size of the passivation opening, increasing the thickness of Cu underbump metallization (UBM), and adopting or inserting a thin highly resistive UBM layer. It was found that the current crowding effect in the solder bump could be successfully relieved with the thick Cu UBM or with the highly resistive UBM. Compared to the solder joint with Al/Ni(V)/Cu UBM, for instance, the maximum current density in a solder bump decreased dramatically by a factor of fifteen, say from 1.11 x 10(5) A/cm(2) to 7.54 x 10(3) A/cm(2) when a 20-pm-thick Cu UBM was used. It could be lowered by a factor of seven, say to 1.55 x 10(4) A/cm(2), when a 0.7-mu m UBM of 14770 mu Omega cm was adopted. It is worth noting that although a resistive UBM layer was used, the penalty on overall resistance increase was negligible because the total resistance was dominated by the Al trace instead of the solder bump. Thermal simulation showed that the average temperature increase due to Joule heating effect was only 2.8 degrees C when the solder joints with UBM of 14770 mu Omega cm were applied by 0.2 A.
Temperature and current-density distributions in flip-chip solder joints with Cu traces
(2006-05-01)
Hsu, CY
;
Yao, DJ
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Liang, SW
;
Chen, C
;
Yeh, ECC
Three-dimensional simulation was performed to investigate the temperature and current density distribution in flip-chip solder joints with Cu traces during current stressing. It was found that the Cu traces can reduce the Joule heating effect significantly at high stressing currents. When the solder joints were stressed by 0.6 A, the average temperature increase in solder bumps with the Al traces was 26.7 degrees C, and it was deceased to 18.7 degrees C for the solder joint with the Cu traces. Hot spots exist in the solder near the entrance points of the Al or Cu traces. The temperature increases in the hot spot were 29.3 degrees C and 20.6 degrees C, for solder joints with the Al traces and Cu traces, respectively. As for current density distribution, the maximum current density inside the solder decreased slightly from 1.66 X 10(5) A/cm(2) to 1.46 X 10(5) A/cm(2) when the Al traces were replaced by the Cu traces. The solder joints with the Cu traces exhibited lower Joule heating and current crowding effects than those with the Al traces, which was mainly attributed to the lower electrical conductivity of the Cu traces. Therefore, the solder joints with the Cu traces are expected to have better electromigration resistance.