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Research Papers

Influence of Glass Transition Temperature of Underfill on the Stress Behavior and Reliability of Microjoints Within a Chip Stacking Architecture

[+] Author and Article Information
Jing-Yao Chang

Industrial Technology Research Institute,
No. 195, Sec. 4, Chung-Hsing Road,
Chutung, Hsinchu 31040, Taiwan;
Institute of Materials Science and Engineering,
National Taiwan University,
No. 1, Sec. 4, Roosevelt Road,
Taipei 10617, Taiwan

Shin-Yi Huang

Industrial Technology Research Institute,
No. 195, Sec. 4, Chung-Hsing Road,
Chutung, Hsinchu 31040, Taiwan

Chang-Chun Lee

Department of Mechanical Engineering,
Research Center for Microsystem Engineering,
Chung Yuan Christian University,
200, Chungpei Road,
Chungli, Taoyuan 32023, Taiwan

Tung-Han Chuang

Institute of Materials Science and Engineering,
National Taiwan University,
No. 1, Sec. 4, Roosevelt Road,
Taipei 10617, Taiwan

Tao-Chih Chang

Industrial Technology Research Institute,
No. 195, Sec. 4 , Chung-Hsing Road,
Chutung, Hsinchu 31040, Taiwan
e-mail: TaoChih@itri.org.tw

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received September 30, 2014; final manuscript received March 15, 2015; published online May 21, 2015. Assoc. Editor: Eric Wong.

J. Electron. Packag 137(3), 031007 (Sep 01, 2015) (8 pages) Paper No: EP-14-1083; doi: 10.1115/1.4030392 History: Received September 30, 2014; Revised March 15, 2015; Online May 21, 2015

In this study, the reliability performance of two capillary-type underfill materials with different glass transition temperatures (Tg) and coefficients of thermal expansion (CTE) were assessed for a chip stacking architecture. The microbumps for integrating four chips on a Si interposer were with a pitch size of 20 μm and composed of 5 μm Cu/3 μm Ni/5 μm Sn2.5Ag solder cap. A thermocompressive bonder was used to interconnect the microbumps at 280 °C for 15 s, and the microgaps between the chips and the interposer were then, respectively, sealed by the mentioned underfill materials to form a chip stacking architecture. Then, the reliability characteristics of the test vehicles were evaluated following the preconditioning and temperature cycling test (TCT). Furthermore, a numerical analysis model was established by ansys software to study the stress and strain contours of the microjoints sealed by different underfill materials. It was found that the lifetime of microjoints was highly related to the Tg points of underfills, an interfacial fracture was observed within the microjoints sealed by a lower Tg underfill after temperature cycling because the tensile strength damaged the Sn depletion zone as heated.

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References

Figures

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Fig. 1

Nonlinear and temperature-dependent stress and strain curve of Sn2.5Ag microbump [17]

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Fig. 2

3D quarter simulation model and boundary conditions established in this work

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Fig. 3

Geometry of the microjoints

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Fig. 4

Distribution of equivalent plastic strain in the outer microjoints for comparison of underfill A (left) and underfill B (right)

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Fig. 5

Equivalent plastic strain accumulation of the outermost microjoint for a comparison of underfill A and underfill B

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Fig. 6

Scanning acoustic microscope (SAM) images of the microgaps sealed by underfill A: (a) before reliability test and (b) after reliability test

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Fig. 7

SAM images of the microgaps sealed by underfill B: (a) before reliability test and (b) after reliability test

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Fig. 8

Failed rate of samples as experienced temperature cycling

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Fig. 9

Weibull distribution of the microjoints sealed by two different underfill materials under TCT test

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Fig. 10

Cross-sectional image of the survival microjoint sealed by underfill B after 3000 temperature cycles

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Fig. 11

Cross-sectional image of the failed sample sealed by underfill B after 3000 temperature cycles

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Fig. 12

SEM morphology of the as-bonded microjoint

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Fig. 13

Elemental mapping analyses of Sn and Ni in a microjoint experienced reliability test

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