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Microstructural evolution and change in macroscopic physical properties of microscale flip chip Cu/Sn58Bi/Cu joints under the coupling effect of electric current stressing and elastic stress

Published online by Cambridge University Press:  16 July 2019

Shui-Bao Liang
School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China
Chang-Bo Ke
School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China
Cheng Wei
School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China; and School of Civil Engineering and Transportation, South China University of Technology, Guangzhou 510640, China
Jia-Qiang Huang
School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China
Min-Bo Zhou
School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China
Xin-Ping Zhang*
School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China
a)Address all correspondence to this author. e-mail:
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Severe phase coarsening and separation in Sn–Bi alloys have brought increasing reliability concern in microelectronic packages. In this study, a phase field model is developed to simulate the microstructural evolution and evaluate the change in macroscopic physical properties of the flip chip Cu/Sn58Bi/Cu joint under the conditions of isothermal aging, as well as the coupled loads of elastic stress and electric current stressing. Results show that large-sized Bi-rich phase particles grow up at the expense of small-sized ones. Under the coupled loads, Bi atoms migrate along the electron flow direction, consequently Bi-rich phase segregates to form a Bi-rich phase layer at the anode. The current crowding ratio in the solder decreases rapidly first and then fluctuates slightly with time. Current density and von Mises stress exhibit inhomogeneous distribution, and both of them are higher in the Sn-rich phase than in the Bi-rich phase. Electric current transfers through the Sn-rich phase and detours the Bi-rich phase. As time proceeds, the resistance of the solder joint increases, and the average von Mises stress of the solder joint decreases. The Bi-rich phase coarsens much faster under the coupled loads than under the conditions of isothermal aging.

Copyright © Materials Research Society 2019 

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