2025

Vol.31 No.4

Editorial Office

Review

  • Journal of the Microelectronics and Packaging Society
  • Volume 31(4); 2024
  • Article

Review

Journal of the Microelectronics and Packaging Society 2024;31(4):96-102. Published online: Jan, 22, 2025

Reliability of Fatigue Deformation for Flexible Cu Interconnect Varying Interfacial Adhesion

  • HeoJeong A, HyunJun Hyeok, KimChae Young, JeonShin Hye, LeeSo-Yeon
    Department of Materials Science and Engineering, Kumoh National Institute of Technology, 61, Daehak-ro, Gumi-si, Gyeongsangbuk-do 39177, Republic of Korea
Corresponding author E-mail: soyeonlee@kumoh.ac.kr
Abstract

Modern electronic devices have evolved to be mechanically flexible, capable of withstanding repetitive deformation. This advancement necessitates ensuring the long-term reliability of metal interconnects, which are essential components in flexible electronic devices. In this study, we analyzed the fatigue behavior of U-shaped structures under tensile conditions, focusing on modifications at the interface between copper (Cu) films and polyimide (PI) substrates. The U-folding fatigue method, which involves complete flattening and bending of the sample compared to U-sliding fatigue, better simulates the actual fatigue deformation occurring during flexible device usage. We compared two adhesion enhancement methods: oxygen plasma treatment and chromium (Cr) adhesion layer introduction. The interfacial adhesion was quantitatively evaluated through nanoscratch tests, while fatigue failure mechanisms were investigated using electrical resistance measurements and microstructural analysis. Our findings revealed that under fatigue strain of 1.0%, the Cr adhesion layer exhibited the highest adhesion strength and showed significant improvement in fatigue resistance. This research provides essential guidance for enhancing the long-term reliability of flexible electronic devices by suggesting effective methods to improve fatigue resistance under practical usage conditions.

Keywords Flexible substrate, Metal interconnect, Adhesion, Reliability, Deformation mechanism

REFERENCES
  • D. Corzo, T.-B. Guillermo, B. Derya, Flexible electronics: status, challenges and opportunities, Frontiers in Electronics, 1 (2020)
  • J. Chen, C. T. Liu, Technology advances in flexible displays and substrates, IEEE Access, 1 (2013)
  • J. G. Seol, D. J. Lee, T. W. Kim, B.-J. Kim, Reliability study on rolling deformation of ITO thin film on flexible substrate, J. Microelectron. Packag. Soc., 25 (2018)
  • J. G. Seol, B.-J. Kim, Electrical Reliability of ITO Film on Flexible Substrate During bending Deformations and Bending Fatigue, J. Microelectron. Packag. Soc., 24 (2017)
  • W. Y. Kwon, B.-J. Kim, Mechanical and Electrical Failure of ITO Film with Different Shape during Twisting Deformation, J. Microelectron. Packag. Soc., 24 (2017)
  • Y.-W. Kown, B.-J. Kim, Mechanical Fatigue Lifetime of Metal Electrode for Flexible Electronics under High Temperature and High Humidity Condition, J. Microelectron. Packag. Soc., 27 (2020)
  • Y.-J. Park, G.-J. Jeong, K.-S. Kim, Research Trends in Thermal Interface Materials for Flexible and Stretchable Electronic Device, J. Microelectron. Packag. Soc., 31 (2024)
  • W. J. Kim, G. S. Hwang, J. Y. Kim, Y. C. Kim, Elastic Properties Evaluation of Thin Films on Flexible Substrates with Consideration of Contact Morphology in Nanoindentation, J. Microelectron. Packag. Soc., 27 (2020)
  • W.-J. Lee, S.-M. Lee, S.-K. Kang, Soft interconnection technologies in flexible electronics, J. Microelectron. Packag. Soc., 29 (2022)
  • B.-J. Kim, Reliability of Metal Electrode for Flexible Electronics, J. Microelectron. Packag. Soc., 20 (2013)
  • J. Yu, M. Ree, T. J. Shin, X. Wang, W. Cai, D. Zhou, K. W. Lee, Miscibility of polyimide with polymeric primer and its influence on adhesion of polyimide to the primed copper metal: Effect of precursor origin, J. Polym. Sci., Part B: Polym. Phys., 37 (1999)
  • H. S. Patel, V. C. Patel, Polyimides containing s-triazine ring, Eur. Polym. J., 37 (2001)
  • S. H. Kim, S. H. Cho, N.-E. Lee, H. M. Kim, Y. W. Nam, Y.-H. Kim, Adhesion properties of Cu/Cr films on polyimide substrate treated by dielectric barrier discharge plasma, Surf. Coat. Technol., 193 (2005)
  • S. H. Kim, S. W. Na, N.-E. Lee, Y. W. Nam, Y.-H. Kim, Effect of surface roughness on the adhesion properites of Cu/Cr films on polyimide substrate treated by inductively coupled oxygen plasma, Surf. Coat. Technol., 200 (2005)
  • T. Miyamura, J. Koike, The effects of Cr oxidation and polyimide degradation on interface adhesion strength in Cu/Cr/polyimide flexible films, Mater. Sci. Eng. A, 445–446 (2007)
  • M. J. Kim, J. H. Hyun, J. A. Heo, S. Y. Lee, Reliability of Cu Interconnect under Compressive Fatigue Deformation Varying Interfacial Adhesion Treatment, J. Microelectron. Packag. Soc., 30 (2023)
  • T.-W. Kim, J.-S. Lee, Y.-C. Kim, Y.-C. Joo, B.-J. Kim, Bending strain and bending fatigue lifetime of flexible metal electrodes on polymer substrates, Materials, 12 (2019)
  • V. M. Marx, F. Toth, A. Wiesinger, J. Berger, C. Kirchlechner, M. J. Cordill, F. D. Fischer, F. G. Rammerstorfer, G. Dehm, The influence of a brittle Cr interlayer on the deformation behavior of thin Cu films on flexible substrates: Experiment and model, Acta Mater., 89 (2015)
  • O. Kraft, R. Schwaiger, P. Wellner, Fatigue in Thin Films: Lifetime and Damage Formation, Mater. Sci. Eng. A, 319-321 (2001)
  • B. J. Kim, H. A. S. Shin, S. Y. Jung, Y. Cho, O. Kraft, I. S. Choi, Y. C. Joo, Crack nucleation during mechanical fatigue in thin metal films on flexible substrate, Acta Mater., 61 (2013)
  • B. J. Kim, H. A. S. Shin, J. H. Lee, Y. C. Joo, Effect of cyclic outer and inner bending on the fatigue behavior of a multilayer metal film on a polymer substrate, J. Appl. Phys., 55 (2016)
  • B.-J. Kim, H. A. S. Shin, J. H. Lee, T.-Y. Yang, T. Haas, P. A. Gruber, I. S. Choi, O. Kraft, Y. C. Joo, Effect of film thickness on the stretchability and fatigue resistance of Cu films on polymer substrates, J. Mater. Res., 29 (2014)
  • V. M. Marx, C. Kirchlechner, I. Zizak, M. J. Cordill, G. Dehm, Adhesion measurement of a buried Cr interlayer on polyimide, Phil. Mag., 95 (2015)