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Nondestructive Evaluation of Thermal Phase Growth in Solder Ball Micro-Joints by Synchrotron Radiation X-Ray Micro-Tomography

[+] Author Affiliations
Toshihiko Sayama

Toyama Industrial Technology Center, Toyama, Toyama, Japan

Hiroyuki Tsuritani

Toyama Industrial Technology Center, Takaoka, Toyama, Japan

Kentaro Uesugi

SPring-8, Japan Synchrotron Radiation Research Institute (JASRI), Sayo, Hyogo, Japan

Akira Tsuchiyama

Osaka University, Toyonaka, Osaka, Japan

Tsukasa Nakano

National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan

Hideyuki Yasuda

Osaka University, Suita, Osaka, Japan

Takeshi Takayanagi

Cosel Company, Ltd., Toyama, Toyama, Japan

Takao Mori

Toyama Prefectural University, Kosugi, Toyama, Japan

Paper No. IPACK2005-73083, pp. 1115-1121; 7 pages
  • ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems collocated with the ASME 2005 Heat Transfer Summer Conference
  • Advances in Electronic Packaging, Parts A, B, and C
  • San Francisco, California, USA, July 17–22, 2005
  • Conference Sponsors: Heat Transfer Division and Electronic and Photonic Packaging Division
  • ISBN: 0-7918-4200-2 | eISBN: 0-7918-3762-9
  • Copyright © 2005 by ASME


In high-density packaging technology, one of the most important problems is reliability of the micro-joints connecting LSI (Large Scale Integrated Circuit) chips to PCBs (Printed Circuit Boards) electrically and mechanically. Development of nondestructive testing methods with high spatial resolution is expected to enhance the reliability. Our research group has developed an X-ray micro-tomography system called SP-μCT at the beamline BL47XU in SPring-8, the largest synchrotron radiation facility in Japan. In this work, SP-μCT was applied to three-dimensional evaluation of microstructure evolution; that is, phase growth due to thermal cyclic loading in solder ball micro-joints. Simulating solder micro-joints 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 observation of the CT images obtained consecutively at the fixed point of the target joining. In the reconstructed CT images, the distribution of the constituent phases in Sn-Pb eutectic solder was identified based on the estimation value of the X-ray linear attenuation coefficient. The following results were obtained. First, each phase involves not dispersing particles but a three-dimensionally monolithic structure just like a sponge. Second, the phase growth proceeds in such a way that the average phase size to the 4th power increases proportionally to the number of cycles. Finally, in the vicinity of the joining interface, more rapid phase growth occurs in comparison to the other regions because local thermal strain due to the mismatch of thermal expansion leads to remarkable phase growth. Consequently, the microstructure images obtained by SP-μCT bring us useful information to evaluate the reliability of micro-joints.

Copyright © 2005 by ASME



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