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Research Papers

Electromigration Reliability of 96.5Sn–3Ag–0.5Cu Flip-Chip Solder Joints With Au/Ni/Cu or Cu Substrate Pad Metallization

[+] Author and Article Information
Yi-Shao Lai2

Central Laboratories, Advanced Semiconductor Engineering, Inc., 26 Chin 3rd Road, Nantze Export Processing Zone, Kaohsiung 811, Taiwanyishao_lai@aseglobal.com

Ying-Ta Chiu, Chiu-Wen Lee

Central Laboratories, Advanced Semiconductor Engineering, Inc., 26 Chin 3rd Road, Nantze Export Processing Zone, Kaohsiung 811, Taiwan

2

Corresponding author.

J. Electron. Packag 131(2), 021002 (Mar 27, 2009) (5 pages) doi:10.1115/1.3103945 History: Received April 13, 2008; Revised October 16, 2008; Published March 27, 2009

Designed experiments were conducted in this paper to study the effect of Au/Ni/Cu or Cu substrate pad metallization on the electromigration reliability of 96.5Sn–3Ag–0.5Cu flip-chip solder joints with Ti/Ni(V)/Cu under bump metallurgy (UBM) under a current stressing condition with an average current density of around 5kA/cm2 at an ambient temperature of 150°C. Cross-sectional observations on current-stressed solder joints indicate that although Cu metallization results in severe voiding compared with Au/Ni/Cu metallization on the substrate side of the solder joint, the dominant failure has been identified as UBM consumption, and test vehicles with Cu metallization exhibit better electromigration reliability than those with Au/Ni/Cu metallization. The stronger durability against current stressing for test vehicles with Cu metallization may attribute to the lower UBM consumption rate due to the continuous Cu diffusion toward UBM as a result of the concentration gradient. The consumption of UBM is faster for test vehicles with Au/Ni/Cu metallization because Cu diffusion from the substrate pad is retarded by the Ni barrier.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Layout of circuits and solder joints

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Figure 2

Electrified daisy chain and direction of current flow

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Figure 3

Typical resistance changes for test vehicles with Cu (left) and Au/Ni/Cu metallization (right)

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Figure 4

SAT images for failed test vehicles with Cu (upper) and Au/Ni/Cu (lower) metallization

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Figure 5

Typical electromigration-induced failure; Au/Ni/Cu metallization

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Figure 6

Weibull cumulative distributions

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Figure 7

Voids in Cu3Sn IMC in V2+ joint with Cu metallization; η=9363 h

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Figure 8

Voids in Cu3Sn IMC in V2−/V3+ joint with Cu metallization; η=9363 h

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Figure 9

IMC structure in V2+ joint with Au/Ni/Cu metallization; η=3471 h

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Figure 10

Voiding on interface between solder and Cu metallization in V1− joint; η=9363 h

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Figure 11

IMC structure in V1− joint with Au/Ni/Cu metallization; η=3471 h

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