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Research Papers

Application of Synchrotron Radiation X-Ray Microtomography to Nondestructive Evaluation of Thermal Fatigue Process in Flip Chip Interconnects

[+] Author and Article Information
Hiroyuki Tsuritani

 Machinery and Electronics Research Institute, Toyama Industrial Technology Center, 383 Takata, Toyama-shi, Toyama 930-0866, 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

Yoshiyuki Okamoto

 On-Board Standard Design Department, Cosel Co., Ltd., 1-6-43 Kamiakae-machi, Toyama-shi, Toyama 930-0816, Japanokamotoyoshiyuki@cosel.co.jp

Takeshi Takayanagi

 On-Board Standard Design Department, Cosel Co., Ltd., 1-6-43 Kamiakae-machi, Toyama-shi, Toyama 930-0816, Japantakayanagi@cosel.co.jp

Kentaro Uesugi

SPring-8,  Japan Synchrotron Radiation Research Institute (JASRI), 1-1-1 Koto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japanueken@spring8.or.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 133(2), 021007 (Jun 23, 2011) (9 pages) doi:10.1115/1.4003992 History: Received August 11, 2010; Revised March 26, 2011; Published June 23, 2011; Online June 23, 2011

New nondestructive inspection methods with high spatial resolution are expected to support the evaluation and enhancement of the reliability of microjoints on printed circuit boards. An X-ray microtomography system, the SP-μCT has been developed at the Super Photon ring-8 GeV (SPring-8), the largest synchrotron radiation facility in Japan. In this work, the SP-μCT was first applied to the nondestructive evaluation of thermal fatigue phenomena, namely microstructure evolution (i.e., phase growth) and microcrack propagation, appearing in actual solder microbumps of flip chip interconnects due to thermal cyclic loading. In addition, a refraction-contrast imaging technique was simultaneously applied to visualize the fatigue cracks with an actual opening of less than 100 nm. The observed specimen has a flip chip structure joined by Sn-37wt%Pb eutectic solder bumps 150 μm in diameter. Consequently, the process of phase growth and crack propagation was determined via observation of consecutive computed tomography (CT) images obtained in the same plane of the same specimen. As the thermal cycle proceeded, remarkable phase growth was clearly observed, followed by the appearance of fatigue cracks in the corners of the interfaces between the solder bump and Cu pad. Moreover, the CT images also enabled us to evaluate the fatigue lifetime of the bumps, as follows. The lifetime to fatigue crack initiation was estimated by quantifying the increase in the phase growth. The crack propagation lifetime to failure was then determined by measuring the average crack propagation rate. Such results have not been obtainable at all by X-ray CT systems for industrial use and demonstrate the possibility of nondestructive inspection by a synchrotron radiation X-ray microtomography system.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic view of an X-ray micro-tomography system, the SP-μCT at SPring-8

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Figure 2

Principle of refraction-contrast imaging

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Figure 3

Schematic view of a specimen

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Figure 4

Volume-rendered image of a flip chip specimen

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Figure 5

Comparison between the CT and SEM images at the same cross section in the same solder bump loaded for 100 cycles

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Figure 6

Comparison between the CT and SEM images showing fatigue cracks at the same cross section in the same solder bump loaded for 500 cycles

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Figure 7

CT images of the same solder bump showing the phase growth process due to thermal cyclic loading. Here, grayscale indicates the X-ray LAC level.

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Figure 8

The phase growth process in solder bumps represented by phase growth parameter S

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Figure 9

CT images of the same solder bump showing the fatigue crack propagation process due to thermal cyclic loading. Here, grayscale indicates the X-ray LAC level.

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Figure 10

3D rendered images of the fatigue crack propagation process in the same solder bump due to thermal cyclic loading

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Figure 11

Crack propagation process in solder bumps represented by crack length

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