Browsing by Author "Yao, DJ"

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Electromigration in pb-free SnAg3.8Cu0.7 solder stripes
(2005-08-01)
Hsu, YC
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Chou, CK
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Liu, PC
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Chen, C
;
Yao, DJ
Electromigration behavior in the eutectic SnAg3.8Cu0.7 solder stripes was investigated in the vicinity of the device operation temperature of 100 degrees C by using the edge displacement technique. Measurements were made for relevant parameters for electromigration of the solder, such as drift velocity, threshold current density, activation energy, as well as the product of diffusivity and effective charge number (DZ(*)). The threshold current densities were estimated to be 4.3x10(4) A/cm(2) at 80 degrees C, 3.2x10(4) A/cm(2) at 100 degrees C, and 1.4x10(4) A/cm(2) at 120 degrees C. These values represent the maximum current densities that the SnAg3.8Cu0.7 solder can carry without electromigration damage at the three stressing temperatures. The electromigration activation energy was determined to be 0.45 eV in the temperature range of 80-120 degrees C. The measured products of diffusivity and the effective charge number, DZ(*), were -1.8x10(-10) cm(2)/s at 80 degrees C, -5.0x10(-10) cm(2)/s at 100 degrees C, and -7.2x10(-10) cm(2)/s at 120 degrees C. (c) 2005 American Institute of Physics.
Infrared microscopy of hot spots induced by Joule heating in flip-chip SnAg solder joints under accelerated electromigration
(2006-01-09)
Chiu, SH
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Shao, TL
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Chen, C
;
Yao, DJ
;
Hsu, CY
Joule heating effect in solder joints was investigated using thermal infrared microscopy and modeling in this study. With the increase of applied current, the temperature increased rapidly due to Joule heating. Furthermore, modeling results indicated that a hot spot existed in the solder near the entrance point of the Al trace, and it became more pronounced as the applied current increased. The temperature difference between the hot spot and the solder was as large as 9.4 degrees C when the solder joint was powered by 0.8 A. This hot spot may play an important role in the initial void formation during electromigration.
Temperature and current-density distributions in flip-chip solder joints with Cu traces
(2006-05-01)
Hsu, CY
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Yao, DJ
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Liang, SW
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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.
Thermal gradient in solder joints under electrical-current stressing
(2004-11-01)
Shao, TL
;
Chiu, SH
;
Chen, C
;
Yao, DJ
;
Hsu, CY
The thermal gradient and temperature increase in SnAg3.5 solder joints under electrical-current stressing have been investigated by thermal infrared microscopy. Both positive and negative thermal gradients were observed under different stressing conditions. The magnitude of the thermal gradient increases with the applied current. The measured thermal gradients reached 365degreesC/cm as powered by 0.59 A, yet no obvious thermal gradient was observed when the joints were powered less than 0.25 A. The temperature increase caused by joule heating was as high as 54.5degreesC when powered by 0.59 A, yet only 3.7degreesC when stressed by 0.19 A. The location of heat generation and path of heat dissipation are believed to play crucial roles in the thermal gradient. When the major heat source is the Al trace, the thermal gradient in the solder bumps is positive; but it may become negative because the heat generated in the solder itself is more prominent.