| Summary: | 博士 === 國立交通大學 === 材料科學與工程系所 === 94 === Electromigration behavior of lead-free SnAg3.5 solder joints was investigated under the average current densities of 1 �e 104 A/cm2 and 5 �e 103 A/cm2 at 150℃. Different failure modes were observed for the above two stressing conditions. When stressed at 1 �e 104 A/cm2, damage occurred in both anode/chip side and cathode/chip sides. However, failure happened only in the cathode/chip under the stressing of 5 �e 103 A/cm2. Three-dimensional simulation of current density distribution by finite element method was performed to provide better understanding of current crowding behavior in the solder joint. The local maximum current density of flip chip solder joint was as high as 1.24×105 A/㎝2 under the stressing of 1 �e 104 A/cm2. And the location of the maximum current density occurred in the vicinity of the Al entrance into the solder joint. In addition, both temperature increases and thermal gradients were measured during the two stressing conditions. The measured temperature increase due to Joule heating was as high as 54.5 ℃, and the thermal gradients reached 365 ℃/cm when stressed by 1 �e 104 A/cm2. Joule heating plays an important role in the failure mechanism during higher current stressing. Possible mechanisms responsible for the different failure modes are proposed.
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