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Mechanism of electromigration-induced failure in flip-chip solder joints with a 10-μm-thick Cu under-bump metallization

Published online by Cambridge University Press:  03 March 2011

Jae-Woong Nah ,
Kai Chen ,
K.N. Tu ,
Bor-Rung Su  and
Chih Chen
Jae-Woong Nah*
Affiliation:
Department of Materials Science and Engineering, University California at Los Angeles, Los Angeles, California 90095-1595
Kai Chen
Affiliation:
Department of Materials Science and Engineering, University California at Los Angeles, Los Angeles, California 90095-1595
K.N. Tu
Affiliation:
Department of Materials Science and Engineering, University California at Los Angeles, Los Angeles, California 90095-1595
Bor-Rung Su
Affiliation:
Department of Materials Science and Engineering, National Chiao Tung University, Taiwan 30050, People’s Republic of China
Chih Chen
Affiliation:
Department of Materials Science and Engineering, National Chiao Tung University, Taiwan 30050, People’s Republic of China
*
a)Address all correspondence to this author. e-mail: jnah@us.ibm.com
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Abstract

The electromigration-induced failure in flip-chip eutectic SnPb solder joints with a 10-μm-thick Cu under-bump metallization (UBM) was studied without the effect of current crowding in the solder region. The current crowding occurred inside the UBM instead of in the solder joint at the current density of 3.0 × 104 A/cm2 because of the spreading of current in the very thick Cu UBM. In these joints, the failure occurred through a two-stage consumption of the thick Cu UBM in the joint where electrons flowed from the chip to the substrate. In the first stage, the Cu UBM dissolved layer by layer rather uniformly across the entire Cu UBM–solder interface. In the second stage, after half of the Cu UBM was dissolved, an asymmetrical dissolution of Cu UBM took place at the corner where electrons entered from the Al interconnect to the Cu UBM. Experimental observation of dissolution steps of the 10-μm-thick Cu UBM is presented. The transition from the first stage to the second stage has been found to depend on the location of current crowding in the flip-chip joints as the UBM thickness changes during the electromigration test. The current distribution in the flip-chip solder joints as a function of UBM thickness was simulated by three-dimensional finite element analysis. The dissolution rate of Cu UBM in the second stage was faster than that in the first stage. The mechanism of electromigration-induced failure in the flip-chip solder joints with a 10-μm-thick Cu UBM is discussed.

Keywords

ElectromigrationPackagingSoldering
Type
Articles
Information
Journal of Materials Research , Volume 22 , Issue 3 , March 2007 , pp. 763 - 769
Copyright
Copyright © Materials Research Society 2007

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References

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