Investigation of Co Thin Film as Buffer Layer Applied to Cu/Sn Eutectic Bonding and UBM with Sn, SnCu, and SAC Solders Joints

Ya Sheng Tang, Jaber Derakhshandeh, Yi Tung Kho, Yao Jen Chang, John Slabbekoorn, Inge De Preter, Kris Vanstreels, Kenneth June Rebibis, Eric Beyne, Kuan-Neng Chen*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


The demand of small-feature-size, high-performance, and dense I/O density applications promotes the development of fine-pitch vertical interconnects for 3-D integration where microbumps are fabricated with Cu through-silicon via and under-bump metallization. Small dimension Cu/Sn bonding has to be developed to address the needs of increasing I/O density and shrinking pitch and size for future applications. For fine-pitch microbumps, it is important to select right UBM and solder materials to obtain lower UBM consumption, which means lower intermetallic compound (IMC) thickness. To find the best binary system material for fine-pitch microbumps with a different annealing temperature and time, we investigate the interfacial reaction and intermetallic compound morphologies of Co UBM with Sn, SnCu, and SAC solders. A thin, uniform, and single-phase IMC between solder and UBM facilitates finer pitch and more reliable microbumps development; the higher activation energies imply longer solder lifetime. Co, as an ultrathin buffer layer (UBL), is also used in Cu/Sn bonding. A comparison between Cu-Sn bonding with and without UBL is conducted. From this study, Co as UBL and UBM is explored and could be applied in semiconductor applications.

Original languageEnglish
Article number8024028
Pages (from-to)1899-1905
Number of pages7
JournalIEEE Transactions on Components, Packaging and Manufacturing Technology
Issue number11
StatePublished - 1 Nov 2017


  • 3-D integration
  • binary solders
  • fine-pitch microbumps
  • ultrathin buffer layer (UBL)
  • under-bump metallization (UBM)

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