Journal of the Microelectronics and Packaging Society (마이크로전자및패키징학회지)

The Korean Microelectronics and Packaging Society (한국마이크로전자및패키징학회)
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Thermo-mechanical Behavior of WB-PBGA Packages with Pb-Sn Solder and Lead-free Solder Using Moire Interferometry

무아레 간섭계를 이용한 유연 솔더와 무연 솔더 실장 WB-PBGA 패키지의 열-기계적 변형 거동

  • Lee, Bong-Hee (Department of Mechanical Engineering, Chungbuk National University) ;
  • Kim, Man-Ki (Department of Mechanical Engineering, Chungbuk National University) ;
  • Joo, Jin-Won (Department of Mechanical Engineering, Chungbuk National University)
  • Received : 2010.08.10
  • Accepted : 2010.08.30
  • Published : 2010.09.30
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Abstract

Pb-Sn solder is rapidly being replaced by lead-free solder for board-level interconnection in microelectronic package assemblies due to the environmental protection requirement. There is a general lack of mechanical reliability information available on the lead-free solder. In this study, thermo-mechanical behaviors of wire-bond plastic ball grid array (WB-PBGA) package assemblies are characterized by high-sensitivity moire interferometry. Experiments are conducted for two types of WB-PBGA packages that have Pb-Sn solder and lead-free solder as joint interconnections. Using real-time moire setup, fringe patterns are recorded and analyzed for several temperatures. Bending deformations of the assemblies and average strains of the solder balls are investigated and compared for the two type of WB-PBGA package assemblies. Results show that shear strain in #3 solder ball located near the chip shadow boundary is dominant for the failure of the package with Pb-Sn solder, while normal strain in #7 most outer solder ball is dominant for that with lead-free solder. It is also shown that the package with lead-free solder has much larger bending deformation and 10% larger maximum effective strain than the package with Pb-Sn solder at same temperature level.

반도체 패키지에 사용되고 있는 유연 솔더는 환경 보호 필요성 대문에 무연 솔더로 빠르게 대체되고 있다. 이와 같은 무연 솔더에 대한 여구는 주로 재료의 발견과 공정 적응성의 관점에서 이루어졌을 뿐, 기계적인 성질이나 신뢰성의 관점에서의 연구는 많이 이루어지지 않았다. 본 논문에서는 무아레 간섭계를 이용하여 유연 솔더와 무연 솔더 실장 WB-PBGA 패키지 결합체의 온도변화에 대한 열-기게적 거동을 해석하였다. 실시간 무아레 간섭계를 이용하여 각 온도 단계에서 변위 분포를 나타내는 간섭무늬를 얻고, 그로부터 유연과 무연의 솔더 조인트를 갖는 WB-PBGA 패키지의 굽힘 변형 거동 및 솔더 볼의 변형률을 비교 분석하였다. 분석결과를 보면 유연 솔더 실장 패키지 결합체의 솔더 볼은 칩경계 부근인 #3 솔더 볼에서 발생하는 전단변형률이 파손에 큰 영향을 미치며, 무연 솔더가 실장된 패키지 결합체의 솔더 볼은 가장 바깥 부근인 #7 솔더 볼에서 발행하는 수직 변형률이 파손에 큰 영향을 미칠 것으로 예측된다, 또한 무연 솔더 실장 패키지 결합체는 같은 온도 조건에서 유연 솔더 실장된 패키지에 비해 굽힘 변형이 휠씬 크게 발생될 뿐 아니라 솔더 볼의 유효변형률도 10% 정도 크게 발생하는 것으로 나타나서 열변형에 의한 파손에 취약할 것으로 예측된다.

Keywords

Acknowledgement

Supported by : 한국연구재단

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