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Thermomigration of Cu–Sn and Ni–Sn intermetallic compounds during electromigration in Pb-free SnAg solder joints

Published online by Cambridge University Press:  30 March 2011

Hsiao-Yun Chen  and
Chih Chen
Hsiao-Yun Chen
Affiliation:
Department of Materials Science and Engineering, National Chiao Tung University, Hsin-chu 30010, Taiwan, Republic of China
Chih Chen*
Affiliation:
Department of Materials Science and Engineering, National Chiao Tung University, Hsin-chu 30010, Taiwan, Republic of China
*
a)Address all correspondence to this author. e-mail: chih@mail.nctu.edu.tw
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Abstract

Thermomigration in Pb-free SnAg solder alloys is investigated during accelerated electromigration tests under 9.7 × 103 A/cm2 at 150 °C. It is found that Cu–Sn intermetallic compounds (IMCs) migrate toward the cold end on the substrate side and, as a result, voids accumulate in the chip side for the bump with current flowing from the substrate end to the chip end. Theoretical calculations indicate that the thermomigration force is greater than the electromigration force at a thermal gradient above 400 °C/cm for this stressing condition. Copper atoms may migrate against current flow and become the dominant diffusion species. On the other hand, Ni–Sn IMCs did not migrate even under a huge thermal gradient of 1400 °C/cm. These findings provide more understanding on the thermomigration of metallization materials in flip-chip solder joints.

Keywords

PackagingDiffusion
Type
Articles
Information
Journal of Materials Research , Volume 26 , Issue 8 , 28 April 2011 , pp. 983 - 991
Copyright
Copyright © Materials Research Society 2011

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