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Research Papers

Current Crowding and its Effects on Electromigration and Interfacial Reaction in Lead-Free Solder Joints

[+] Author and Article Information
Hao Lu

School of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai 200030, P.R.C.shweld@sjtu.edu.cn

Chun Yu, Peilin Li, Junmei Chen

School of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai 200030, P.R.C.

J. Electron. Packag 130(3), 031008 (Aug 01, 2008) (5 pages) doi:10.1115/1.2957322 History: Received June 04, 2007; Revised December 03, 2007; Published August 01, 2008

The current density distribution in a line-to-bump structure as a function of cross-sectional area ratio of the electrical conductor was investigated, as well as the effects of current crowding on electromigration and interfacial reaction in lead-free solder joints. Finite element analysis shows that the crowding factor is directly proportional to the cross-sectional area ratio between Cu line and contact opening at the cathode side. CuSn3.0Ag0.5CuCu solder joints with Cu line in different widths were designed and tested under 1×103Acm2 at 60°C for 430h. The experiment results show that big voids induced by electromigration are only formed at the structure with a narrower line. Moreover, the growth of intermetallic compound layers, as well as dissolution of Cu at the cathode side, is accelerated by smaller current crowding, whereas impeded by a bigger one.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 7

Diffusion model at the cathode side

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Figure 6

Microstructure of the interface under EM test on the cathode side. The average current density is 1×103A∕cm2 and temperature is 60°C for 430h. (a) Linewidth of 300μm; (b) linewidth of 100μm.

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Figure 5

Cross-sectional morphology of the Cu∕Sn3.0Ag0.5Cu∕Cu joint

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Figure 4

Relationship of the crowding factor and area ratio

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Figure 3

Cross-sectional distributions of the current density, (a) for Cu line width of 300μm and (b) for Cu line width of 100μm

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Figure 2

(a) 3D finite element model showing the meshes and (b) the tilt view of the current density distribution in the solder joint. Linewidth is 100μm.

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Figure 1

Sketch of the Cu∕Sn3.0Ag0.5Cu∕Cu sandwich structure

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