Pan Pacific Symposium Conference Proceedings


Authors: T. Akamatsu, H. Ueda, M. Ochiai, and E. Horikoshi
Company: Fujitsu Laboratories Ltd.
Date Published: 2/18/2003   Conference: Pan Pacific Symposium

Abstract: We studied the application of Sn-Bi eutectic solder to bump material from the point of view of its original characteristics. The original characteristics of the solder show a volume decrease during transformation from solid to liquid state. With this characteristic in mind, we investgated the volume increase of liquid Sn-Bi eutectic solder during 2nd level packaging with Sn-Ag-Cu solder and found that the volume increase of liquid Sn-Bi eutectic solder to be small when compared with that of Sn-Ag-Cu solder transforming from solid into liquid state.

Therefore it appears that short circuits resulting from volume increase between bumps were preventable. Additionally, we investigated the effect of adding Ag into Sn-Bi eutectic solder, in an attempt to improve its elongation property. We examined the fatigue property mechanism that Ag gave to the Sn-Bi alloy characteristic. We found optimum concentration of Ag in Sn-Bi-Ag solder. We then demonstrated the joint reliability of the flip chip interconnection with an Sn-Bi solder bump. We performed a thermal cycle test. After this testing, we were able to confirm that Sn-Bi solder joint reliability equal to that of Sn-Ag-Cu system solder had been achieved.

Key words: Sn-Bi, flip-chip, reflow.

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