scholarly journals Relieving the current crowding effect in flip-chip solder joints during current stressing

2006 ◽  
Vol 21 (1) ◽  
pp. 137-146 ◽  
Author(s):  
S.W. Liang ◽  
T.L. Shao ◽  
Chih Chen ◽  
Everett C.C. Yeh ◽  
K.N. Tu
Keyword(s):  
Flip Chip ◽  
Solder Bump ◽  
Solder Joints ◽  
Three Dimensional ◽  
Current Crowding ◽  
Crowding Effect ◽  
Average Temperature ◽  
Current Stressing ◽  
Underbump Metallization ◽  
Overall Resistance

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 × 105 A/cm2 to 7.54 × 103 A/cm2 when a 20-μm-thick Cu UBM was used. It could be lowered by a factor of seven, say to 1.55 × 104 A/cm2, when a 0.7-μm UBM of 14770 μΩ 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 °C when the solder joints with UBM of 14770 μΩ cm were applied by 0.2 A.

Secondary Current Crowding Effect during Electromigration of Flip-Chip Solder Joints

2007 ◽  
Vol 37 (2) ◽  
pp. 185-188 ◽  
Author(s):  
J.W. Jang ◽  
L.N. Ramanathan ◽  
J. Tang ◽  
D.R. Frear
Keyword(s):  
Flip Chip ◽  
Solder Joints ◽  
Current Crowding ◽  
Crowding Effect ◽  
Secondary Current

Orientation transformation of Pb grains in 5Sn–95Pb/ 63Sn–37Pb composite flip-chip solder joints during electromigration test

2008 ◽  
Vol 23 (7) ◽  
pp. 1877-1881 ◽  
Author(s):  
Ying-Ta Chiu ◽  
Kwang-Lung Lin ◽  
Yi-Shao Lai
Keyword(s):  
Electron Microscopy ◽  
Driving Force ◽  
Flip Chip ◽  
Solder Bump ◽  
Solder Joints ◽  
Electron Backscatter Diffraction ◽  
Current Stressing ◽  
Electron Backscatter ◽  
Backscatter Diffraction ◽  
Scanning Electron

Microstructural evolution occurred in 5Sn–95Pb/63Sn–37Pb composite flip-chip solder bump during electromigration. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) observations for 5Sn–95Pb/63Sn–37Pb composite flip-chip solder joints subjected to 5 kA/cm2 current stressing at 150 °C revealed a gradual orientation transformation of Pb grains from random textures toward (101) grains. We proposed that the combination of reducing the surface energy of Pb grain boundaries and resistance of the entire polycrystalline system are the driving force for the orientation transformation of Pb grains during an electromigration test.

Mechanism of electromigration-induced failure in flip-chip solder joints with a 10-μm-thick Cu under-bump metallization

2007 ◽  
Vol 22 (3) ◽  
pp. 763-769 ◽  
Author(s):  
Jae-Woong Nah ◽  
Kai Chen ◽  
K.N. Tu ◽  
Bor-Rung Su ◽  
Chih Chen
Keyword(s):  
Flip Chip ◽  
Solder Joints ◽  
Three Dimensional ◽  
Layer By Layer ◽  
Current Crowding ◽  
Under Bump Metallization ◽  
Element Analysis ◽  
Second Stage ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

The electromigration-induced failure in flip-chip eutectic SnPb solder joints with a 10-μm-thick Cu under-bump metallization (UBM) was studied without the effect of current crowding in the solder region. The current crowding occurred inside the UBM instead of in the solder joint at the current density of 3.0 × 104 A/cm2 because of the spreading of current in the very thick Cu UBM. In these joints, the failure occurred through a two-stage consumption of the thick Cu UBM in the joint where electrons flowed from the chip to the substrate. In the first stage, the Cu UBM dissolved layer by layer rather uniformly across the entire Cu UBM–solder interface. In the second stage, after half of the Cu UBM was dissolved, an asymmetrical dissolution of Cu UBM took place at the corner where electrons entered from the Al interconnect to the Cu UBM. Experimental observation of dissolution steps of the 10-μm-thick Cu UBM is presented. The transition from the first stage to the second stage has been found to depend on the location of current crowding in the flip-chip joints as the UBM thickness changes during the electromigration test. The current distribution in the flip-chip solder joints as a function of UBM thickness was simulated by three-dimensional finite element analysis. The dissolution rate of Cu UBM in the second stage was faster than that in the first stage. The mechanism of electromigration-induced failure in the flip-chip solder joints with a 10-μm-thick Cu UBM is discussed.

Damages and Microstructural Variation of High-lead and Eutectic SnPb Composite Flip Chip Solder Bumps Induced by Electromigration

2005 ◽  
Vol 20 (8) ◽  
pp. 2184-2193 ◽  
Author(s):  
Yeh-Hsiu Liu ◽  
Kwang-Lung Lin
Keyword(s):  
Flip Chip ◽  
Solder Bump ◽  
Electron Flow ◽  
Electron Probe Microanalyzer ◽  
Current Stressing ◽  
Solder Bumps ◽  
Underbump Metallization ◽  
Current Polarity ◽  
High Lead ◽  
Eutectic Snpb

The electromigration behavior of the high-lead and eutectic SnPb composite solder bumps was investigated at 150 °C with 5 × 103 A/cm2 current stressing for up to 1711 h. The diameter of the bumps was about 125 μm. The underbump metallization (UBM) on the chip side was sputtered Al/Ni(V)/Cu thin films, and the Cu pad on the board side was plated with electroless Ni/Au. It was observed that damages occurred in the joints in a downward electron flow (from chip side to the substrate side), while those joints having the opposite current polarity showed only minor changes. In the case of downward electron flow, electromigration damages were observed in the UBM and solder bumps. The vanadium in Ni(V) layer was broken under current stressing of 1711 h while it was still intact after current stressing of 1000 h. The electron probe microanalyzer (EPMA) elemental mapping clearly shows that the Al atoms in the trace migrated through the UBM into the solder bump during current stressing. Voids were found in the solder bump near the UBM/solder interface. The Sn-rich phases of the solder bumps showed gradual streaking and reorientation upon current stressing. This resulted in the formation of uniaxial Sn-rich phases in the middle of the solder bump, while the columnar and fibrous Sn-rich phases were formed in the surrounding regions. The formation mechanism of electromigration-induced damage to the UBM structure and solder bump were discussed.

In-situ observation of material migration in flip-chip solder joints under current stressing

2006 ◽  
Vol 35 (10) ◽  
pp. 1781-1786 ◽  
Author(s):  
C. M. Tsai ◽  
Yi-Shao Lai ◽  
Y. L. Lin ◽  
C. W. Chang ◽  
C. R. Kao
Keyword(s):  
Flip Chip ◽  
Solder Joints ◽  
In Situ Observation ◽  
Current Stressing ◽  
Material Migration
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