Journal of the Microelectronics and Packaging Society (마이크로전자및패키징학회지)

The Korean Microelectronics and Packaging Society (한국마이크로전자및패키징학회)
권호 표지
DOI QR코드

DOI QR Code

Warpage of Flexible OLED under High Temperature Reliability Test

고온 신뢰성 시험에서 발생된 플렉서블 OLED의 휨 변형

  • Lee, Mi-Kyoung (Graduate School of NID Fusion Technology, Seoul National University of Science and Technology) ;
  • Suh, Il-Woong (Graduate School of NID Fusion Technology, Seoul National University of Science and Technology) ;
  • Jung, Hoon-Sun (Graduate School of NID Fusion Technology, Seoul National University of Science and Technology) ;
  • Lee, Jung-Hoon (Graduate School of NID Fusion Technology, Seoul National University of Science and Technology) ;
  • Choa, Sung-Hoon (Graduate School of NID Fusion Technology, Seoul National University of Science and Technology)
  • 이미경 (서울과학기술대학교 NID 융합기술대학원) ;
  • 서일웅 (서울과학기술대학교 NID 융합기술대학원) ;
  • 정훈선 (서울과학기술대학교 NID 융합기술대학원) ;
  • 이정훈 (서울과학기술대학교 NID 융합기술대학원) ;
  • 좌성훈 (서울과학기술대학교 NID 융합기술대학원)
  • Received : 2016.02.21
  • Accepted : 2016.03.27
  • Published : 2016.03.30
Download PDF
⟨ Previous Next ⟩

Abstract

Flexible organic light-emitting diode (OLED) devices consist of multi-stacked thin films or layers comprising organic and inorganic materials. Due to thermal coefficient mismatch of the multi-layer films, warpage of the flexible OLED is generated during high temperature process of each layer. This warpage will create the critical issues for next production process, consequently lowering the production yield and reliability of the flexible OLED. In this study, we investigate the warpage behavior of the flexible OLED for each bonding process step of the multi-layer films using the experimental and numerical analysis. It is found that the polarizer film and barrier film show significant impact on warpage of flexible OLED, while the impact of the OCA film on warpage is negligible. The material that has the most dominant impact on the warpage is a plastic cover. In order to minimize the warpage of the flexible OLED, we estimate the optimal material properties of the plastic cover using design of experiment. It is found that the warpage of the flexible OLED is reduced to less than 1 mm using a cover plastic of optimized properties which are the elastic modulus of 4.2 GPa and thermal expansion coefficient of $20ppm/^{\circ}C$.

플렉서블 OLED는 매우 다양한 유기(organic) 및 무기 물질로 이루어져 있으며, 각 층을 증착하는 과정에 의하여 고온에 의한 휨(warpage)이 발생한다. 휨으로 인하여 발생한 굽힘 변형은 후속 공정에 많은 영향을 미치며, 궁극적으로 생산 수율 및 신뢰성을 저하시킨다. 본 연구에서는 플렉서블 OLED 소자의 고온 환경신뢰성 시험 및 공정 단계에서 발생하는 휨 변형을 수치해석을 이용하여 예측하였으며 실험 결과와 비교하였다. 이를 통하여 휨에 가장 큰 영향을 미치는 재료를 파악하고, 궁극적으로 휨을 최소화 함으로써 플렉서블 OLED의 신뢰성을 향상시키고자 하였다. 휨의 측정 및 수치해석 결과, 편광 필름과 베리어 필름이 휨에 많은 영향을 줌을 알 수 있었으며, OCA가 휨에 미치는 영향은 미미하였다. 플렉서블 OLED의 휨에 가장 큰 영향을 주는 소재는 plastic cover이였으며, 휨을 최소화하기 위한 plastic cover 소재의 최적 물성을 실험계획법으로 계산한 결과, 탄성 계수는 4.2 GPa, 열팽창계수는 $20ppm/^{\circ}C$ 일 경우 플렉서블 OLED의 휨은 1 mm 이하가 됨을 알 수 있었다.

Keywords

References

  1. G. P. Crawford, Editor, "Flexible flat panel displays", Wiley, Chichester (2005).
  2. J. H. Ahn, H. Lee, and S. H. Choa, "Technology of flexible semiconductor/memory device", J. Microelectron. Packag. Soc., 20(2), 1 (2013).
  3. Y. Zhang and P. L. P. Rau "Playing with multiple wearable devices: exploring the influence of display, motion and gender", Computers in Human Behavior, 50, 148 (2015). https://doi.org/10.1016/j.chb.2015.04.004
  4. J. H. Kim and J. W. Park, "Improving the flexibility of largearea transparent conductive oxide electrodes on polymer substrates for flexible organic light emitting diodes by introducing surface roughness", Organic Electronics, 14(12), 3444 (2013). https://doi.org/10.1016/j.orgel.2013.09.016
  5. A. W. J. Gielen, M. Barink, J. van den Brand, and A. M. B. van Mol, "The electro-thermal-mechanical performance of an OLED: a multi-physics model study", 10th. Int. Conf. on Thermal, Mechanical and Multiphysics Simulation and Experiments in Micro-Electronics and Micro-Systems, Euro-SimE, 1 (2009).
  6. C. G. Kim, H. S. Choi, M. S. Kim, and T. S. Kim, "Packaging substrate bending prediction due to residual stress", J. Microelectron. Packag. Soc., 20(1), 21 (2013). https://doi.org/10.6117/kmeps.2013.20.1.021
  7. T. Mizutani, T. Ikeda, K. Miyake, and N. Miyazaki, "Warpage analysis of an LCD panel under thermo-mechanical and hygro-mechanical stress", Electronic Materials and Packaging, EMAP 2007. International Conference, 1 (2007).
  8. M. K. Yeh, L. Y. Chang, and M. R. Lu, "Bending stress analysis of flexible touch panel", Microsyst Technol, 20 (8), 1641 (2014). https://doi.org/10.1007/s00542-014-2200-1
  9. C. J. Chiang, C. Winscom, S. Bull, and A. Monkman, "Mechanical modeling of flexible OLED devices", Organic Electronics, 10(7), 1268 (2009). https://doi.org/10.1016/j.orgel.2009.07.003
  10. H. Y. Low, and S. J. Chua, "Mechanical properties of organic light-emitting thin films deposited on polymer-based barrier substrate: potential for flexible organic light-emitting displays", Mater. Lett., 53(4), 227 (2002). https://doi.org/10.1016/S0167-577X(01)00481-5
  11. G. G. Stoney, "The tension of metallic films deposited by electrolysis", Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character, 82(553), 172 (1909).
  12. K. Roll, "Analysis of stress and strain distribution in thin films and substrates", J Appl Phys, 47, 3224 (1974).
  13. C. C. Lee, Y. S. Shih, C. S. Wu, C. H. Tsai, S. T. Yeh, Y. H. Peng, and K. J. Chen, "Development of robust flexible OLED encapsulations using simulated estimations and experimental validations", J. Phys. D: Appl. Phys. 45(27), 275102 (2012). https://doi.org/10.1088/0022-3727/45/27/275102
  14. N. Murata, "Adhesives for optical devices", Electronic Components and Technology Conference, 1178 (1998).
  15. Y. Wang and P. Hassell, "On-line measurement of thermally induced warpage of BGAs with high sensitivity shadow moire", The International Journal of Microcircuits and Electronic Packaging, 21(2), 191 (1998).
  16. W. Lin and M. W. Lee, "PoP/CSP warpage evaluation and viscoelastic modeling", Electronic Components and Technology Conference, 1576 (2008).

Cited by

  1. Measurement of Flexural Modulus of Lamination Layers on Flexible Substrates vol.23, pp.3, 2016, https://doi.org/10.6117/kmeps.2016.23.3.063