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RESEARCH PAPERS

Nondestructive Evaluation of Thermal Phase Growth in Solder Ball Microjoints by Synchrotron Radiation X-Ray Microtomography

[+] Author and Article Information
Hiroyuki Tsuritani

 Central Research Institute, Toyama Industrial Technology Center, 150 Futagami-machi, Takaoka-shi, Toyama 933-0981, Japanturitani@itc.pref.toyama.jp

Toshihiko Sayama

 Machinery and Electronics Research Institute, Toyama Industrial Technology Center, 383 Takata, Toyama-shi, Toyama 930-0866, Japansayama@itc.pref.toyama.jp

Kentaro Uesugi

SPring-8, Japan Synchrotron Radiation Research Institute (JASRI), 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japanueken@spring8.or.jp

Takeshi Takayanagi

Research and Development Department, Cosel Co., Ltd., 1-6-43 Kamiakae-machi, Toyama-shi, Toyama 930-0816, Japantakayanagi@cosel.co.jp

Takao Mori

Department of Mechanical System Engineering, Toyama Prefectural University, 5180 Kurokawa, Imizu-shi, Toyama 939-0398, Japantmori@pu-toyama.ac.jp

J. Electron. Packag 129(4), 434-439 (May 02, 2007) (6 pages) doi:10.1115/1.2804093 History: Received October 04, 2006; Revised May 02, 2007

In high-density packaging technology, one of the most important issues is the reliability of the microjoints connecting large scale integrated circuit chips to printed circuit boards electrically and mechanically. The development of nondestructive testing methods with high spatial resolution is expected to enhance reliability. An X-ray microtomography system called SP-μCT has been developed in Super Photon ring-8 GeV (SPring-8), the largest synchrotron radiation facility in Japan. In this work, SP-μCT was applied in the nondestructive evaluation of microstructure evolution, that is, the phase growth due to thermal cyclic loading in solder ball microjoints. Simulating solder microjoints used in a flip chip, specimens were fabricated by joining a Sn–Pb eutectic solder ball 100 μm in diameter to a steel pin in the usual reflow soldering process. The phase growth process was determined by observing the computed tomography (CT) images obtained consecutively at the fixed point of the target joining. In the reconstructed CT images, the distribution of the constituent phases in the Sn–Pb eutectic solder was identified based on the estimation value of the X-ray linear attenuation coefficient. Consequently, the microstructure images obtained nondestructively by SP-μCT provided us with the following useful information for evaluating the reliability of the solder microjoints. First, each phase involves not dispersing particles but a three-dimensional monolithic structure like a sponge. Second, the phase growth proceeds in such a way that the average phase size to the fourth power increases proportionally to the number of cycles. Finally, in the vicinity of the joining interface, more rapid phase growth occurs compared to the other regions because local thermal strain due to the mismatch of thermal expansion leads to a remarkable phase growth.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic view of an X-ray microtomography system called SP-μCT in SPring-8

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Figure 2

SEM image of the specimen

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Figure 3

Temperature profile of thermal cycle tests

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Figure 4

CT images of a specimen loaded for 300cycles under the acceleration condition. The images are reconstructed in the planes perpendicular to the rotation axis, and each number indicates the distance from the joining.

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Figure 5

Frequency distributions of X-ray LAC at all the voxels inside different solder balls in the initial state

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Figure 6

3D image of the same specimen shown in Fig. 4

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Figure 7

CT images showing the phase growth process of the same specimen. The images are reconstructed in the same plane perpendicular to the rotation axis.

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Figure 8

Frequency distribution change of X-ray LAC inside the same solder ball shown in Fig. 7

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Figure 9

3D images showing the phase growth process of the same specimen shown in Fig. 7

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Figure 10

Phase growth process represented by phase growth parameter S under different thermal cyclic loading conditions

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Figure 11

Phase growth process represented by phase growth parameter S in different slice planes of the same specimen

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Figure 12

Phase growth process represented by phase growth parameter S in slice planes at different distances from the joining interface

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