Browsing by Author "Yeh, ECC"

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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
;
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.