Journal of Electronic Materials

, Volume 41, Issue 2, pp 283–301

The Role of Elastic and Plastic Anisotropy of Sn in Recrystallization and Damage Evolution During Thermal Cycling in SAC305 Solder Joints

Authors

    • Chemical Engineering and Materials ScienceMichigan State University
  • Bite Zhou
    • Chemical Engineering and Materials ScienceMichigan State University
  • Lauren Blair
    • Chemical Engineering and Materials ScienceMichigan State University
  • Amir Zamiri
    • Mechanical EngineeringMichigan State University
  • Payam Darbandi
    • Mechanical EngineeringMichigan State University
  • Farhang Pourboghrat
    • Mechanical EngineeringMichigan State University
  • Tae-Kyu Lee
    • Component Quality and Technology GroupCisco Systems, Inc.
  • Kuo-Chuan Liu
    • Component Quality and Technology GroupCisco Systems, Inc.
Article

DOI: 10.1007/s11664-011-1811-x

Cite this article as:
Bieler, T.R., Zhou, B., Blair, L. et al. Journal of Elec Materi (2012) 41: 283. doi:10.1007/s11664-011-1811-x

Abstract

Because failures in lead-free solder joints occur at locations other than the most highly shear-strained regions, reliability prediction is challenging. To gain physical understanding of this phenomenon, physically based understanding of how elastic and plastic deformation anisotropy affect microstructural evolution during thermomechanical cycling is necessary. Upon solidification, SAC305 (Sn-3.0Ag-0.5Cu) solder joints are usually single or tricrystals. The evolution of microstructures and properties is characterized statistically using optical and orientation imaging microscopy. In situ synchrotron x-ray measurements during thermal cycling are used to examine how crystal orientation and thermal cycling history change strain history. Extensive characterization of a low-stress plastic ball grid array (PBGA) package design at different stages of cycling history is compared with preliminary experiments using higher-stress package designs. With time and thermal history, microstructural evolution occurs mostly from continuous recrystallization and particle coarsening that is unique to each joint, because of the specific interaction between local thermal and displacement boundary conditions and the strong anisotropic elastic, plastic, expansion, and diffusional properties of Sn crystals. The rate of development of recrystallized microstructures is a strong function of strain and aging. Cracks form at recrystallized (random) boundaries, and then percolate through recrystallized regions. Complications arising from electromigration and corrosion are also considered.

Keywords

SnMicrostructureAnisotropyThermal expansionThermal cyclingSlip systemsDamageRecrystallization
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© TMS 2011