2024

Vol.31 No.2

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  • Journal of the Microelectronics and Packaging Society
  • Volume 30(4); 2023
  • Article

Review

Journal of the Microelectronics and Packaging Society 2023;30(4):98-104. Published online: Feb, 20, 2024

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DOI : doi.org/10.6117/kmeps.2023.30.4.098

Fabrication of Porous Cu Layers on Cu Pillars through Formation of Brass Layers and Selective Zn Etching, and Cu-to-Cu Flip-chip Bonding

  • Wan-Geun Lee1 , Kwang-Seong Choi2 , Yong-Sung Eom2 , and Jong-Hyun Lee1†
    1Department of Materials Science & Engineering, Seoul National University of Science and Technology, Seoul 01811, Republic of Korea, 2Low-Carbon Integration Tech, Creative Research Section, ETRI, Daejeon 34129, Republic of Korea
Corresponding author E-mail: pljh@snut.ac.kr
Abstract

The feasibility of an efficient process proposed for Cu-Cu flip-chip bonding was evaluated by forming a porous Cu layer on Cu pillar and conducting thermo-compression sinter-bonding after the infiltration of a reducing agent. The porous Cu layers on Cu pillars were manufactured through a three-step process of Zn plating-heat treatment-Zn selective etching. The average thickness of the formed porous Cu layer was approximately 2.3 µm. The flip-chip bonding was accomplished after infiltrating reducing solvent into porous Cu layer and pre-heating, and the layers were finally conducted into sintered joints through thermo-compression. With reduction behavior of Cu oxides and suppression of additional oxidation by the solvent, the porous Cu layer densified to thickness of approximately 1.1 µm during the thermo-compression, and the CuCu flip-chip bonding was eventually completed. As a result, a shear strength of approximately 11.2 MPa could be achieved after the bonding for 5 min under a pressure of 10 MPa at 300 ℃ in air. Because that was a result of partial bonding by only about 50% of the pillars, it was anticipated that a shear strength of 20 MPa or more could easily be obtained if all the pillars were induced to bond through process optimization.

Keywords Porous Cu layer, Flip-chip bonding, Zn plating, Zn selective etching, Thermo-compression sinter-bonding

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