Journal of the Microelectronics and Packaging Society (마이크로전자및패키징학회지)

The Korean Microelectronics and Packaging Society (한국마이크로전자및패키징학회)
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Control of Position of Neutral Line in Flexible Microelectronic System Under Bending Stress

굽힘응력을 받는 유연전자소자에서 중립축 위치의 제어

  • Seo, Seung-Ho (Department of Nanotechnology and Advanced Materials Engineering, Sejong University) ;
  • Lee, Jae-Hak (Advanced Manufacturing System Research Division, Korea Institute of Machinery & Materials) ;
  • Song, Jun-Yeob (Advanced Manufacturing System Research Division, Korea Institute of Machinery & Materials) ;
  • Lee, Won-Jun (Department of Nanotechnology and Advanced Materials Engineering, Sejong University)
  • 서승호 (세종대학교 나노신소재공학과) ;
  • 이재학 (한국기계연구원 초정밀시스템연구실) ;
  • 송준엽 (한국기계연구원 초정밀시스템연구실) ;
  • 이원준 (세종대학교 나노신소재공학과)
  • Received : 2016.05.23
  • Accepted : 2016.06.20
  • Published : 2016.06.30
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Abstract

A flexible electronic device deformed by external force causes the failure of a semiconductor die. Even without failure, the repeated elastic deformation changes carrier mobility in the channel and increases resistivity in the interconnection, which causes malfunction of the integrated circuits. Therefore it is desirable that a semiconductor die be placed on a neutral line where the mechanical stress is zero. In the present study, we investigated the effects of design factors on the position of neutral line by finite element analysis (FEA), and expected the possible failure behavior in a flexible face-down packaging system assuming flip-chip bonding of a silicon die. The thickness and material of the flexible substrate and the thickness of a silicon die were considered as design factors. The thickness of a flexible substrate was the most important factor for controlling the position of the neutral line. A three-dimensional FEA result showed that the von Mises stress higher than yield stress would be applied to copper bumps between a silicon die and a flexible substrate. Finally, we suggested a designing strategy for reducing the stress of a silicon die and copper bumps of a flexible face-down packaging system.

유연전자소자가 외부힘에 의해 변형될 경우 반도체 다이가 기계적 응력 때문에 변형되거나 파괴되고 이러한 변형이나 파괴는 channel의 전자이동도를 변화시키거나 배선의 저항을 증가시켜 집적회로의 동작 오류를 발생시킨다. 따라서 반도체 집적회로는 굽힘 변형이 발생해도 기계적 응력이 발생하지 않는 중립축에 위치하는 것이 바람직하다. 본 연구에서는 굽힘변형을 하는 flip-chip 접합공정이 적용된 face-down flexible packaging system에서 중립축의 위치와 파괴 모드를 조사하였고 반도체 집적회로와 집중응력이 발생한 곳의 응력을 감소시킬 수 있는 방법을 제시하였다. 이를 위해, 설계인자로 유연기판의 두께 및 소재, 반도체 다이의 두께를 고려하였고 설계인자가 중립축의 위치에 미치는 영향을 조사한 결과 유연기판의 두께가 중립축의 위치를 조절하는데 유용한 설계인자임을 알 수 있었다. 3차원 모델을 이용한 유한요소해석 결과 반도체 다이와 유연기판 사이의 Cu bump 접합부에서 항복응력보다 높은 응력이 인가될 수 있음을 확인하였다. 마지막으로 flexible face-down packaging system에서 반도체 다이와 Cu bump 의 응력을 감소시킬 수 있는 설계 방법을 제안하였다.

Keywords

References

  1. T. S. Kim, J. H. Kim, T. E. Kang, C. Y. Lee, H. B. Kang, M. K. Shin, C. Wang, B. Ma, U. Y. Jeong, T. S. Kim and B. J. Kim, "Flexible, Highly Efficient All-polymer Solar Cells", Nature Communications, 6, 8547 (2015). https://doi.org/10.1038/ncomms9547
  2. V. M. Marx, F. Toth, A. Wiesinger, J. Berger, C. Kirchlechner, M. J. Cordill, F. D. Fischer, F. G. Rammerstorferc and G. Dehm, "The Influence of a Brittle Cr Interlayer on the Deformation Behavior of Thin Cu Films on Flexible Substrates: Experiment and Model", Acta Materialia, 89, 278 (2015). https://doi.org/10.1016/j.actamat.2015.01.047
  3. S. Endler, H. Rempp, C. Harendt, and J. N. Burghartz, "Compensation of Externally Applied Mechanical Stress by Stacking of Ultra-Thin Chips", Proc. of 41st Euro. Solid-State Devi. Rese. Conf., 279 (2011).
  4. X. J. Sun, C. C. Wang, J. Zhang, G. Liu, G. J. Zhang, X. D. Ding, G. P. Zhang and J. Sun, "Thickness Dependent Fatigue Life at Microcrack Nucleation for Metal Thin Films on Flexible Substrates", J. Appl. Phys., 41, 195404 (2008).
  5. 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. Appl. Phys., 45, 27510 (2012).
  6. N. Palavesam, C. Landesberger and C. Kutter, "Finite Element Analysis of Uniaxial Bending of Ultra Thin Silicon Dies Embedded in Flexible Foil Substrates", Proc. 11th Microelectronics and Electronics (PRIME) Conference, Glasgow, 137, IEEE (2015).
  7. B. J. Kim, H. A. S. Shin, I. S. Choi and Y. C. Joo, "Electrical Failure and Damage Analysis of Multi-Layer Metal Films on Flexible Substrate During Cyclic Bending Deformation", IPFA 18th IEEE Inter. Symp., 2725 (2011).
  8. D. Wang, C. A. Volkert and O. Kraft, "Effect of Length Scale on Fatigue Life and Damage Formation in Thin Cu Films", Mater. Sci. Eng: A, 493(1), 267 (2008). https://doi.org/10.1016/j.msea.2007.06.092
  9. S. M. Lee, J. Y. Kwon, D. S. Yoon, H. D. Cho, J. H. You, Y. T. Kang, D. H. Choi and W. B. Hwang, "Bendability Optimization of Flexible Optical Nanoelectronics Via Neutral Axis Engineering", Nano. Rese. Lett., 7, 256 (2012). https://doi.org/10.1186/1556-276X-7-256
  10. M. Sugano, S. Machiya, M. Sato, T. Koganezawa, K. Shikimachi, N. Hirano and S. Nagaya, "Bending Strain Analysis Considering a Shift of the Neutral Axis for YBCO Coated Conductors With and Without a Cu Stabilizing Layer", Supercond. Sci. Technol., 24, 075019 (2011). https://doi.org/10.1088/0953-2048/24/7/075019
  11. D. A. van den Ende, H. J. van de Wiel, R. H. L. Kusters, A. Sridhar, J. F. M. Schram, M. Cauwe and J. van den Brand, "Bonding Bare Die LEDs on PET Foils for Lighting Applications Thermal Design Modeling and Bonding Experiments", Microelectron. Rel., 54, 2860 (2014). https://doi.org/10.1016/j.microrel.2014.07.125
  12. J. van den Brand, J. de Baets, T. van Mol and A. Dietzel, "Systems-in-Foil-Devices, Fabrication Processes and Reliability Issues", Microelectron. Rel., 48, 1123 (2008). https://doi.org/10.1016/j.microrel.2008.06.030
  13. J. Wolf, J. Kostelnik, K. Berschauer, A. Kugler, E. Lorenz, T. Gneiting, C. Harendt and Z. Yu, "Ultra-Thin Silicon Chips in Flexible Microsystems", ECWC13, (2014).
  14. S. Endler, S. Ferwana, H. Rempp, C. Harendt and J. N. Burghartz, "Two-Dimensional Flex Sensor Exploiting Stacked Ultrathin Chips", IEEE Elec. Devi. Lett., 33, 444 (2012). https://doi.org/10.1109/LED.2011.2178389
  15. F. Hou, X. Zhang, X. Guo, H. Xie, Y. Lu, L. Cao and L. Wan. "Thermo-mechanical reliability study for 3D package module based on flexible substrate", Proc. 14th International Conference on Electronic Packaging Technology (ICEPT), 1296, Dalian, IEEE (2013).
  16. B. J. Kim, M. H. Jeong, S. H. Hwan, H. Y. Lee, S. W. Lee, K. D. Chun, Y. B. Park and Y. C. Joo, "Relationship Between Tensile Characteristics and Fatigue Failure by Folding or Bending in Cu Foil on Flexible Substrate", J. Microelectron. Packag. Soc., 18(1), 55 (2011).
  17. B. J. Kim, "Reliability of Metal Electrode for Flexible Electronics", J. Microelectron. Packag. Soc., 20(4) 1 (2013). https://doi.org/10.6117/KMEPS.2013.20.4.001
  18. S. Kim and T. S. Kim, "Adhesion Reliability Enhancement of Silicon/Epoxy/Polyimide Interfaces for Flexible Electronics", J. Microelectron. Packag. Soc., 19(3), 63 (2012). https://doi.org/10.6117/kmeps.2012.19.3.063