Observation of Electromigration-Induced beta-Sn Microstructure Evolution in Real Solder Joints with Various Joint Sizes

• Main Authors: Chih-Nan Chen, 陳志南
• Other Authors: Cheng-En Ho
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/78717313765009507150

碩士 === 元智大學 === 化學工程與材料科學學系 === 99 === White Tin (beta-Sn) has a body-center tetragonal (BCT) (a = b = 5.83 Å; c = 3.18 Å) structure. Due to the anisotropy, the axis has different properties. In this study, we observation of electromigration-induced beta-Sn microstructure evolution in Cu/Sn/Cu diffusion couple and line-bump flip chip solder joints, respectively. First, Sn grains reorientation has significantly different in Cu/Sn/Cu diffusion couple under the current stressing with time. In early stage, with an increase in grain size, the initially unsteady stage behavior of grain growth Voronoi microstructure approaches the steady stage behavior an equiaxed microstructure. With current stressing time, reorientation of Sn grains to realign themselves so that their c-axis is perpendicular to the current direction. It has been found the Sn grains reorientation starts promptly at the beginning on grain boundary, and expanded moved toward the grain. The Sn grains reorientation mechanism is different from literature, because these phenomenon show a resemblance development of the microstructure to those observed in grain boundary migration (GBM). Interestingly, Sn grains reorientation can be inhibited due to the pinning force resulting from the coherency Cu6Sn5 appeared in the grain boundaries. Second, due to Sn grains that exhibit highly anisotropic behaviors in diffusion properties. Thus, the diffusion of Cu through in different grains orientation combination, resulting in effect of a main perturbation in Cu6Sn5 position on the reaction. The results of this study revealed that the diffusivity cathode bigger then anode when the Cu accumulation in grain boundary and a large Cu6Sn5 reaction region are found. Additionally, the growth of the Cu6Sn5 follows parabolic growth rule, and we propose that the back stress induced in the Cu6Sn5 plays is a significant role. Finally, we observation of electromigration-induced beta-Sn microstructure evolution in line-bump flip chip solder joints. From the theory of Sn grains reorientation in Cu/Sn/Cu diffusion couple, the line-bump flip chip solder joint follow that. Interestingly, it is obvious that the Sn grains orientation is dominated by the grain size.