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Numerical Study on Stress Distribution of SolderJoints Based on Solder Microstructure

Zarghami, Mohammad | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55306 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Nourani, Amir
  7. Abstract:
  8. In the past, lead-based solders with homogeneous and isotropic behavior were used in microelectronic packages. But today, due to the environmental concerns of lead, lead-free solders have been developed, which consist of a high weight percentage (more than 90%) of tin. Tin crystal shows significant anisotropic behavior, which leads to an anisotropic joint response in miniature solder joints with a small number of grains. In the first part of this research, using the crystal plasticity model, the anisotropic plastic response of tin grain was extracted from bulk solder stress-strain curve, then it was implemented in Abaqus software using built-in Hill's anisotropic plasticity model to consider the effect of the anisotropic material model on the fracture load prediction of solder joints. A maximum difference of 5% was observed between the predicted fracture load of the anisotropic plasticity model and the isotropic plasticity model. This was attributed to the small amount of plasticity in mode 1 loading and the high bending stiffness of the adherend layer in the DCB sample. In the second part of this research, the two-parameter fracture mechanics theory was used to quantify the constraint effect in the Q parameter. This quantification led to the aggregation of geometry and loading effects in a single parameter. For example, changing the thickness of the adherend thickness of DCB from 21 mm to 8 mm, led to a change in the Q from -1.2 to -1.45. Also, changing the length of the loading arm from 12.7 mm to 71.1 mm led to a change of Q from -1.13 to -1.3. By using this quantification, the experimental results of previous works, which were only limited to the examined geometry and loading, can be generalized to different geometries and loadings which represent the same Q value. The proof of this claim is the matching of two fracture energy vs. Q curves, obtained from two different geometrical variations (adherent thickness and loading arm) with an error of less than 6%
  9. Keywords:
  10. Solder Joints ; Finite Element Analysis ; Mechanical Stress ; Microstructure ; Grain Anisotropy ; Two Parameter Fracture Mechanics ; Hill's Strain

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