Journal of the Microelectronics and Packaging Society (마이크로전자및패키징학회지)

The Korean Microelectronics and Packaging Society (한국마이크로전자및패키징학회)
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A Numerical Study on the Effect of Initial Shape on Inelastic Deformation of Solder Balls under Various Mechanical Loading Conditions

다양한 기계적 하중조건에서 초기 형상이 솔더볼의 비탄성 변형에 미치는 영향에 관한 수치적 연구

  • Da-Hun Lee (School of Mechanical Engineering, Sungkyunkwan University) ;
  • Jae-Hyuk Lim (School of Mechanical Engineering, Sungkyunkwan University) ;
  • Eun-Ho Lee (School of Mechanical Engineering, Sungkyunkwan University)
  • 이다훈 (성균관대학교 기계공학부) ;
  • 임재혁 (성균관대학교 기계공학부) ;
  • 이은호 (성균관대학교 기계공학부)
  • Received : 2023.12.13
  • Accepted : 2023.12.30
  • Published : 2023.12.30
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Abstract

Ball Grid Array (BGA) is a widely used package type due to its high pin density and good heat dissipation. In BGA, solder balls play an important role in electrically connecting the package to the PCB. Therefore, understanding the inelastic deformation of solder balls under various mechanical loads is essential for the robust design of semiconductor packages. In this study, the geometrical effect on the inelastic deformation and fracture of solder balls were analyzed by finite element analysis. The results showed that fracture occurred in both tilted and hourglass shapes under shear loading, and no fracture occurred in all cases under compressive loading. However, when bending was applied, only the tilted shape failed. When shear and bending loads were combined with compression, the stress triaxiality was maintained at a value less than zero and failure was suppressed. Furthermore, a comparison using the Lagrangian-Green strain tensor of the critical element showed that even under the same loading conditions, there was a significant difference in deformation depending on the shape of the solder ball.

BGA(ball grid array)는 높은 집적도와 우수한 방열 성능을 갖고 있어 널리 이용되는 방식의 패키지이다. BGA에서 솔더볼은 패키지와 PCB를 전기적으로 연결하는 중요한 역할을 하므로, 다양한 기계적 하중 하에서 솔더볼의 비탄성 변형을 이해하는 것은 반도체 패키지의 강건설계에 필수적이다. 본 연구에서는 공정 중 PCB의 휨, die와 substrate 간의 열팽창 계수 차이 등으로 인해 소성변형이 발생한 솔더볼의 초기 형상이 비탄성 변형과 파단에 미치는 영향을 유한요소 해석으로 분석하였다. 시뮬레이션 결과, shear와 bending 하중에서 tilted, hourglass 형상 모두 파단이 발생한 반면, compression 하중이 작용하는 경우는 모두 파단이 발생하지 않았다. Shear와 bending 하중에 compression이 각각 결합될 경우, 응력삼축비가 0보다 작은 값으로 유지되어 파단이 억제되었다. 또한 변형에 취약한 요소의 Lagrangian-Green 변형률 텐서를 이용해 비교한 결과, 동일한 하중 조건이라도 솔더볼의 형상에 따라 변형의 양상에 유의미한 차이가 있음을 확인하였다.

Keywords

Acknowledgement

This work was partially supported by the Korea Institute for Advancement of Technology (KIAT) grant (P0008458, HRD Program for Industrial Innovation) funded from the Ministry of Trade, Industry & Energy (MOTIE, Korea), and the Technology Innovation Program (Public-private joint investment semiconductor R&D program (K-CHIPS) to foster high-quality human resources) (RS-2023-00236091, Hybrid bonding technologies for 3D package interconnects).

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