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Research Papers

The Effect of Intermetallic Growth on Bump Pull Test Responses of SAC105 Solder Bumps

[+] Author and Article Information
Jose Omar S. Amistoso

Department of Mining, Metallurgy and Materials Engineering, University of the Philippines, Diliman, Quezon City 1101, Philippinesjose_omar.s.amistoso@up.edu.ph

Alberto V. Amorsolo

Department of Mining, Metallurgy and Materials Engineering, University of the Philippines, Diliman, Quezon City 1101, Philippinesalberto_jr.amorsolo@up.edu.ph

J. Electron. Packag 131(4), 041004 (Oct 21, 2009) (6 pages) doi:10.1115/1.4000206 History: Received January 04, 2009; Revised May 03, 2009; Published October 21, 2009

Cold bump pull tests performed on wafer level chip scale packages using SAC105 solder bumps show an increase in the occurrence of brittle failure modes with aging temperature and time. Fast intermetallic growth at 0–1000 h can be attributed to (Cu,Ni)6Sn5, while the decrease in intermetallic growth rate at t>1000h can be attributed to diffusion processes leading to (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 formation and growth. Ni diffuses toward the solder bulk and saturates at 175200°C, while Cu diffuses from the under bump metallization (UBM) toward the solder bump at 125150°C. Interactions between Cu and Ni atoms lead to saturation of their atomic % gradients due to intermetallic formation. Sn diffusion from the solder toward the UBM occurs at 125150°C. The activation energy for total intermetallic growth was calculated at 0.2 eV.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic diagram of a bump pull test setup

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Figure 2

Typical SEM photos of intermetallics at different aging times: (a) 0 h intermetallics SEM photo, (b) 1000 h intermetallics SEM photo at 125°C, (c) 1000 h intermetallics SEM photo at 150°C, (d) 1000 h intermetallics SEM photo at 175°C, and (e) 1000 h intermetallics SEM photo at 200°C

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Figure 3

Plots of average intermetallic thickness versus time at different temperature settings

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Figure 4

Plots of average intermetallic thickness versus time1/2

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Figure 5

Plot of ln(k) versus −1/kBT showing an activation energy of 0.2 eV (slope of the line)

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Figure 6

Typical intermetallic SEM image showing two regions of interest

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Figure 7

Ni atomic % gradients as a function of time at different temperature settings

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Figure 8

Cu atomic % gradients as a function of time at different temperature settings

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Figure 9

Sn atomic % gradients as a function of time at different temperature settings

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Figure 10

Calculated results of Cu concentration drop as a function of time at different aging temperatures

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Figure 11

Observed solder bump failure modes

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Figure 12

Distribution of solder bump failure modes as a function of bump pull test speed

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Figure 13

Distribution of solder bump failure as a function of aging time at different aging temperatures (bump pull speed is 1000 mm/s)

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