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Experimental Study and Finite Element Modeling of the Effect of Microstructure on Fracture Behavior and Fracture Load Prediction of Solder Joints

Mohammadi Amiri, Mostafa | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52798 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Farrahi, Gholamhossein; Nourani, Amir
  7. Abstract:
  8. The critical strain energy release rate for the solder joint fracture was measured as a function of cooling rate, time above liquidus (TAL) and soldering temperature. The specimens were prepared at 4 different levels of cooling rate, 3 varying levels of TAL, and 3 soldering temperature levels. Then, experiments were designed using the Taguchi method. Fracture tests were performed under bending at a strain rates of 10-5 and 0.5 s-1 and mode I loading conditions. It was found that the effect of soldering temperature insignificant on the Jci, but the cooling rate and the TAL due to their many effects were also studied by their interaction effects. It was observed that at the cooling rate of 34°C/s and at both strain rates, increasing the TAL from 60 to 240 s reduced the Jci. Because at this cooling rate it was found that the microstructure of the solder was weak and the fracture was governed by the thickness of the intermetallic compound (IMC). Also, at rates of 0.1 and 1.4°C/s, increasing TAL from 60 to 120 s decreases Jci, which is due to the ductile fracture at TAL60 s due to the smaller thickness of IMC. Increasing the cooling rate from 0.1 to 34°C/s resulted in a decrease in Jci at all 3 TALs and at both strain rates. Because in this case the fracture was controlled by the microstructure of the solder in addition to the thickness of IMC. The TAL changed only the thickness of IMC, but the cooling rate affected both the thickness of IMC and the microstructure of the solder. Increasing the strain rate from quasi-static to intermediate, increased the Jci due to creep deformations in the quasi-static strain rate. Finally, the prediction of the fracture load was made as function of the solder microstructure with the cohesive zone model (CZM). This model was able to predict with an error of less than 11%, except where their microstructure was very different from the calibrated specimens
  9. Keywords:
  10. Fracture Energy ; Cooling Rate ; Microstructure ; Intermetallic Compounds ; Cohesive Zone Model ; Solder Joints ; Connections Fracture

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