Journal of the Microelectronics and Packaging Society (마이크로전자및패키징학회지)

The Korean Microelectronics and Packaging Society (한국마이크로전자및패키징학회)
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Development of Polymer Elastic Bump Formation Process and Bump Deformation Behavior Analysis for Flexible Semiconductor Package Assembly

유연 반도체 패키지 접속을 위한 폴리머 탄성범프 범핑 공정 개발 및 범프 변형 거동 분석

  • Lee, Jae Hak (Dept. of Ultra-Precision Machines and Systems, Advanced Manufacturing Systems Research Division Korea Institute of Machinery and Materials (KIMM)) ;
  • Song, Jun-Yeob (Dept. of Ultra-Precision Machines and Systems, Advanced Manufacturing Systems Research Division Korea Institute of Machinery and Materials (KIMM)) ;
  • Kim, Seung Man (Dept. of Ultra-Precision Machines and Systems, Advanced Manufacturing Systems Research Division Korea Institute of Machinery and Materials (KIMM)) ;
  • Kim, Yong Jin (Dept. of Ultra-Precision Machines and Systems, Advanced Manufacturing Systems Research Division Korea Institute of Machinery and Materials (KIMM)) ;
  • Park, Ah-Young (Dept. of Ultra-Precision Machines and Systems, Advanced Manufacturing Systems Research Division Korea Institute of Machinery and Materials (KIMM))
  • 이재학 (한국기계연구원 초정밀시스템연구실) ;
  • 송준엽 (한국기계연구원 초정밀시스템연구실) ;
  • 김승만 (한국기계연구원 초정밀시스템연구실) ;
  • 김용진 (한국기계연구원 초정밀시스템연구실) ;
  • 박아영 (한국기계연구원 초정밀시스템연구실)
  • Received : 2019.06.12
  • Accepted : 2019.06.25
  • Published : 2019.06.30
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Abstract

In this study, polymer elastic bumps were fabricated for the flexible electronic package flip chip bonding and the viscoelastic and viscoplastic behavior of the polymer elastic bumps according to the temperature and load were analyzed using FEM and experiments. The polymer elastic bump is easy to deform by the bonding load, and it is confirmed that the bump height flatness problem is easily compensated and the stress concentration on thin chip is reduced remarkably. We also develop a spiral cap type and spoke cap type polymer elastic bump of $200{\mu}m$ diameter to complement Au metal cap crack phenomenon caused by excessive deformation of polymer elastic bump. The proposed polymer elastic bumps could reduce stress of metal wiring during bump deformation compared to metal cap bump, which is completely covered with metal wiring because the metal wiring on these bumps is partially patterned and easily deformable pattern. The spoke cap bump shows the lowest stress concentration in the metal wiring while maintaining the low contact resistance because the contact area between bump and pad was wider than that of the spiral cap bump.

본 연구에서는 유연한 접속부를 갖는 유연전자 패키지 플립칩 접속을 위해 폴리머 탄성범프를 제작하였으며, 범프의 온도 및 하중에 따른 폴리머 탄성 범프의 점탄성 및 점소성 거동을 해석 및 실험적으로 분석하고 비교 평가하였다. 폴리머 탄성 범프는 하중에 의한 변형이 용이하여 범프 높이 평탄도 오차의 보정이 용이할 뿐만 아니라 소자가 형성된 칩에 가해지는 응력 집중이 감소하는 것을 확인하였다. 폴리머 탄성 범프의 과도한 변형에 따른 Au Metal Cap Crack 현상을 보완하여 $200{\mu}m$ 직경의 Spiral Cap Type, Spoke Cap type 폴리머 탄성 범프 형성 기술을 개발하였다. 제안된 Spoke Cap, Spiral Cap 폴리머 탄성 범프는 폴리머 범프 전체를 금속 배선이 덮고 있는 Metal Cap 범프에 비해 범프 변형에 의한 응력 발생이 적음을 확인할 수 있으며 이는 폴리머 범프 위의 금속 배선이 부분적으로 패터닝되어 있어 쉽게 변형될 수 있는 구조이므로 응력이 완화되는데 기인하는 것으로 판단된다. Spoke cap type 범프는 패드 접촉부와 전기적 접속을 하는 금속 배선 면적이 Spiral Cap type 범프에 비해 넓어 접촉 저항을 유지하면서 동시에 금속 배선에 응력 집중이 가장 낮은 결과를 확인하였다.

Keywords

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Fig. 1. Overview of PEB face-down interconnection process.

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Fig. 2. Von-Mises stress analysis of single bump package at 3-μm displacement at 25℃.

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Fig. 3. Von-Mises stress analysis of single bump package at 3-μm displacement at 225℃.

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Fig. 4. Deformation behavior analysis of polymer elastic bump w.r.t. bonding force and temperature.

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Fig. 5. Elastic polymer bump design with various type of bump metal pattern.

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Fig. 6. Elastic deformation shape of various type of PEB w.r.t. temperature.

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Fig. 6. Continued.

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Fig. 7. Von-Mises stress of various bump metal patterns w.r.t. temperature.

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Fig. 7. Continued.

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Fig. 8. Calculated Polymer elastic bump contact area variation w.r.t. bump metal pattern and bonding force per bump.

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Fig. 9. Fabrication process of polymer elastic bump chip.

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Fig. 10. Shapes of polymer bumps after thermal reflow process depending on film thickness.

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Fig. 11. Polymer elastic bump shape before and after thermal reflow depending on photoresist volume.

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Fig. 12. Polymer bump diameter and height measured after thermal reflow process at photoresist thickness of 28 μm.

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Fig. 13. Fabricated Polymer elastic bump(PEB) shape by thermal reflow process.

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Fig. 14. Experimental set-up for investigation of polymer elastic bump deformation behavior using micro-tribometer.

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Fig. 15. CCD Images of contact area variation of polymer elastic bump due to bump deformation w.r.t. bump load at 25℃.

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Fig. 16. Results of deformation behavior of circle bump cap with a microtribometer test according to temperature and load.

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Fig. 17. Metal pattern crack images and 3D shape profile of polymer elastic bumps w.r.t temperature.

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Fig. 17. Continued.

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Fig. 18. Method for measuring contact resistance and measured contact resistance depending on bump cap shape.

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Fig. 19. Cross-section images of bonded glass chip and FPCB with polymer elastic bump.

Table 1. Contact diameter depending on temperature and load [μm]

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References

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