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Localized recrystallization and cracking of lead-free solder interconnections under thermal cycling

Published online by Cambridge University Press:  16 August 2011

Hongtao Chen
Affiliation:
Department of Electronic, Aalto University School of Science and Technology, FIN-00076 Aalto, Finland; and Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China
Maik Mueller
Affiliation:
Electronics Packaging Laboratory (IAVT), Technische Universität Dresden, 01062 Dresden, Germany
Tonu Tuomas Mattila*
Affiliation:
Department of Electronic, Aalto University School of Science and Technology, FIN-00076 Aalto, Finland
Jue Li
Affiliation:
Department of Electronic, Aalto University School of Science and Technology, FIN-00076 Aalto, Finland
Xuwen Liu
Affiliation:
Laboratory of Materials Science, Department of Materials Science and Engineering, Aalto University School of Chemical Technology, FIN-00076 Aalto, Finland
Klaus-Juergen Wolter
Affiliation:
Electronics Packaging Laboratory (IAVT), Technische Universität Dresden, 01062 Dresden, Germany
Mervi Paulasto-Kröckel
Affiliation:
Department of Electronic, Aalto University School of Science and Technology, FIN-00076 Aalto, Finland
*
a)Address all correspondence to this author. e-mail: Toni.Mattila@hut.fi
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Abstract

The failure mechanism of lead-free solder interconnections of chip scale package–sized Ball Grid Array (BGA) component boards under thermal cycling was studied by employing cross-polarized light microscopy, scanning electronic microscopy, electron backscatter diffraction, and nanoindentation. It was determined that the critical solder interconnections were located underneath the chip corners, instead of the corner most interconnections of the package, and the highest strains and stresses were concentrated at the outer neck regions on the component side of the interconnections. Observations of the failure modes were in good agreement with the finite element results. The failure of the interconnections was associated with changes of microstructures by recrystallization in the strain concentration regions of the solder interconnections. Coarsening of intermetallic particles and the disappearance of the boundaries between the primary Sn cells were observed in both cases. The nanoindentation results showed lower hardness of the recrystallized grains compared with the non-recrystallized regions of the same interconnection. The results show that failure modes are dependent on the localized microstructural changes in the strain concentration regions of the interconnections and the crack paths follow the networks of grain boundaries produced by recrystallization.

Type
Articles
Copyright
Copyright © Materials Research Society 2011

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References

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