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un-Soo Kim, Yutaka Tsukada, and Katsuaki Suganuma Institute of Science and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan

Kimihiro Yamanaka Kyocera SLC Technologies Corporation, Advanced Packaging Laboratory, Yasu, Shiga 520-2362, Japan

Soichi Kuritani Espec Corporation, Electronic Device System Sales Engineering Department, Kita Ward, Osaka 530-8550, Japan

Minoru Ueshima Senju Metal Industry Co., Ltd., Senjuhasidocho, Tokyo 270-0021, Japan (Received 18 October 2010; accepted 15 November 2010)

Electromigration behavior and fast circuit failure with respect to crystallographic orientation of Sn grains were examined. The test vehicle was Cu/Sn–3.0 wt% Ag–0.5 wt% Cu/Cu ball joints, and the applied current density was 15 kA/cm2 at 160 °C. The experimental results indicate that most of the solder bumps show different microstructural changes with respect to the crystallographic orientation of Sn grains. Fast failure of the bump occurred due to the dissolution of the Cu circuit on the cathode side caused by the fast interstitial diffusion of Cu atoms along the c-axis of the Sn grains when the c-axis was parallel to the electron flow. Slight microstructural changes were observed when the c-axis was perpendicular to the electron flow. In addition, Cu6Sn5 intermetallic compound (IMC) was formed along the direction of the c-axis of the Sn grains instead of the direction of electron flow in all solder ball joints.

I. INTRODUCTION

With the trend of miniaturization and the need for high-performance electronic devices, electronic packaging requires higher input/output (I/O) interconnections, smaller feature size, and better performance. Flip-chip packages are a promising solution to these demands, and they have been proven to provide a good electrical and thermal performance.1 However, more I/O interconnections will be needed for better performance of electronic devices in the near future, and the joint area of each individual solder bump will continue to decrease quickly. At present, the size of each solder bump is 100 lm or less in diameter, and each solder joint is designed to carry 0.2 A.2 However, the difference in electrical resistance and feature size between the solder and the adjacent trace causes a drastic increase in the current density and leads to serious electromigration (EM) damage near the contact area between the line and the bump.3 The actual current density through the solder joint may approach almost 104 A/cm2 or more with decrease in the bump size. In addition, the temperature of these solder joints often reaches 100 °C during device operation as Joule heating is proportional to a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2010.86 J. Mater. Res., Vol. 26, No. 3, Feb 14, 2011

http://journals.cambridge.org

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the square of the current density. As a consequence, under such high current density and high operation temperature, diffusion of atoms can occur easily. Hence, EM is becoming more important as a relia