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Research Papers

Electromigration Reliability With Respect to Cu Weight Contents of Sn–Ag–Cu Flip-Chip Solder Joints Under Comparatively Low Current Stressing

[+] Author and Article Information
Yi-Shao Lai1

Central Labs, Advanced Semiconductor Engineering, Inc., 26 Chin 3rd Road, Nantze Export Processing Zone, Nantze, Kaohsiung, 811 Taiwan, R.O.C.yishao̱lai@aseglobal.com

Ying-Ta Chiu

Central Labs, Advanced Semiconductor Engineering, Inc., 26 Chin 3rd Road, Nantze Export Processing Zone, Nantze, Kaohsiung, 811 Taiwan, R.O.C.

1

Corresponding author.

J. Electron. Packag 130(4), 041001 (Nov 13, 2008) (5 pages) doi:10.1115/1.2957325 History: Received August 01, 2007; Revised January 07, 2008; Published November 13, 2008

This work presents electromigration reliability and patterns of Sn–3Ag–0.5Cu and Sn3Ag1.5CuSn3Ag0.5Cu composite flip-chip solder joints with TiNi(V)Cu under bump metallurgy (UBM), bonded on AuNiCu substrate pads. The solder joints were subjected to an average current density of 5kAcm2 under an ambient temperature of 150°C. Under the situation when electron charges flow from the UBM toward the substrate, Sn diffuses from the Cu–Ni–Sn intermetallic compound developed around the UBM toward the UBM and eventually causes the Ni(V) layer to deform. Electromigration reliability of Sn3Ag1.5CuSn3Ag0.5Cu composite flip-chip solder joints was found to be better than that of Sn–3Ag–0.5Cu solder joints. According to the morphological observations on cross-sectioned solder joints, a failure mechanism is proposed as follows. Since the deformation of the Ni(V) layer as a result of Sn diffusion toward the UBM is considered as the dominant failure, a greater Cu weight content in the solder joints would trap more Sn in the Sn–Cu interfacial reaction and would therefore retard the diffusion of Sn toward the UBM and hence enhance the electromigration reliability.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Layout of circuits and joints

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Figure 2

Electrified daisy chain and directions of dc current and electron charge flow

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Figure 3

Weibull cumulative distributions for electromigration reliability of Sn–3Ag–0.5Cu and Sn–3Ag 1.5Cu cells

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Figure 4

V1–Sn–3Ag–0.5Cu solder joint after current stressing for 2250h

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Figure 5

V1+Sn–3Ag–0.5Cu solder joint after current stressing for 2250h

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Figure 6

Closed-up view of area A for V1+Sn–3Ag–0.5Cu solder joint

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Figure 7

V1–Sn–3Ag–1.5Cu solder joint after current stressing for 3900h

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Figure 8

V1+Sn–3Ag–1.5Cu solder joint after current stressing for 3900h

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Figure 9

Closed-up view of area B for V1–Sn–3Ag–1.5Cu solder joint

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Figure 10

Closed-up view of area C for V1+Sn–3Ag–1.5Cu solder joint

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