Effect of metal bond-pad configurations on the solder microstructure development of flip-chip solder joints

Y. J. Hu, Y. C. Hsu, T. S. Huang, C. T. Lu, Albert T. Wu, C. Y. Liu

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Various microstructural zones were observed in the solidified solder of flip-chip solder joints with three metal bond-pad configurations (Cu/Sn/Cu, Ni/Sn/Cu, and Cu/Sn/Ni). The developed microstructures of the solidified flip-chip solder joints were strongly related to the associated metal bond pad. A hypoeutectic microstructure always developed near the Ni bond pad, and a eutectic or hypereutectic microstructure formed near the Cu pad. The effect of the metal bond pads on the solder microstructure alters the Cu solubility in the molten solder. The Cu content (solubility) in the molten Sn(Cu) solder eventually leads to the development of particular microstructures. In addition to the effect of the associated metal bond pads, the developed microstructure of the flip-chip solder joint depends on the configuration of the metal bond pads. A hypereutectic microstructure formed near the bottom Cu pad, and a eutectic microstructure formed near the top Cu pad. Directional cooling in the flip-chip solder joint during the solidification process causes the effects of the metal bond-pad configuration. Directional cooling causes the Cu content to vary in the liquid Sn(Cu) phase, resulting in the formation of distinct microstructural zones in the developed microstructure of the flip-chip solder joint.

Original languageEnglish
Pages (from-to)170-175
Number of pages6
JournalJournal of Electronic Materials
Volume43
Issue number1
DOIs
StatePublished - Jan 2014

Keywords

  • flip chip
  • IC packaging
  • lead-free solder
  • microstructure

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