Browsing by Author "Zhan, C. J."

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Analysis of bump resistance and current distribution of ultra-fine-pitch microbumps
(2013-01-01)
Chang, Y. W.
;
Peng, H. Y.
;
Yang, R. W.
;
Chen, Chih
;
Chang, T. C.
To keep up with the demand of continuous increase in device densities, the integration of three-dimensional integrated circuits (3D-IC) has become the most probable solution, and the utilization of ultra-fine-pitch microbump has emerged as an essential component of 3D-IC technology. In this study, a Kelvin bump structure was fabricated and resistances measured at different angles on a 20.0 mu m microbump were investigated. The microbump resistance at 0 degrees, 60 degrees, 120 degrees, and 180 degrees are 74.7, 45.9, 14.6, and 13.7 m Omega, respectively. These high resistances in microbumps may result in high interconnect resistance and cause resistance/capacitance (RC) delay, and thus lower the electrical performance of 3D-IC. A series of finite-element-model (FEM) was built to analyze the distribution of electric field in microbump. The FEM results have shown that the current is distributed uniformly in the thin solder joint, but current crowding still occurs in the Cu under-bump-metallization (UBM). The finding of the current crowding in the Cu UBM is the main cause of high resistances in the microbump. Thickening the Al trace, for example, from 0.4 mu m to 1.5 mu m, is a direct solution to reduce the unexpected high microbump resistance. A numerical model which treated solder joints as a resistance network was also performed in this study. For comparison, both FEM and the numerical model show the same trend and agree with the measurement results from Kelvin bump structure. The results all point to one thing: thickening the Al trace turn out to be the most effective approach to reduce high microbump resistance. When the Al trace thickness is increased from 0.8 to 3.0 mu m, the microbump resistance is decreased to half of the original value, resulted from the alleviation of current crowding in the Cu UBM. (C) 2012 Elsevier Ltd. All rights reserved.
Fast phase transformation due to electromigration of 18 mu m microbumps in three-dimensional integrated-circuit integration
(2014-12-15)
Chang, Y. W.
;
Chen, Chih
;
Chang, T. C.
;
Zhan, C. J.
;
Juang, J. Y.
The electromigration behavior was investigated in 18-mu m SnAg microbumps at 150 degrees C. The monitored resistance increase abruptly soon after the current stressing of 4.6 x 10(4) A/cm(2) was applied but the resistance rose much slower after a certain period of time. The formation of the high-resistivity Ni3Sn4 intermetallic compounds (IMCs) was responsible for the abrupt resistance increase in the beginning of the current stressing. The whole solder joint was transformed into an IMC joint. Because IMC has a higher electromigration resistance than the solder, a much slower increase in resistance was resulted after the solder joint was transformed into IMCs. (C) 2014 Elsevier B.V. All rights reserved.