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Effect of Environmental Conditions on Fracture Behavior of Solder Joints

Honarvar, Sobhan | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53655 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Nourani, Amir
  7. Abstract:
  8. Double cantilever beam (DCB) specimens were prepared according to standard surface mount technology (SMT). The samples were stored inside an environmental chamber at two different relative humidity values (i.e. 40 or 100%) for either 2 or 4 hours. Then they were aged at 25ºC, 75ºC or 125℃ for the same time. Finally, after being cooled to room temperature, fracture tests were performed under mode-I loading conditions at a strain rate of 0.03 s-1 at room temperature. Storage time did not have a significant effect on the fracture behavior. The fracture load and energy of the solder joints decreased significantly when the temperature was increased from 25 to 75℃. By further increase in the temperature from 75 to 125℃, the fracture strength slightly increased. This behavior was attributed to the thickness of intermetallic compound (IMC) as well as the portion of brittle phases on the joint microstructure. The influence of relative humidity on the fracture strength was less than the temperature effect due to coarsening behavior of microstructure with a humidity rise. The fracture surface of the specimen stored at a temperature of 25℃ and relative humidity of 40% was flat and smooth, while in other cases, the fracture surfaces showed a three-dimensional roughness. Effects of storing specimens at a temperature of 75℃ and cyclic temperature varying between 32 and 75℃ were examined at two different strain rates of 10-5 and 0.03 s-1 under mode-I loading conditions.. It was observed that by storing samples in constant and cyclic temperature for about 4 hours, fracture energy of solder joint decreased significantly in the strain rate of 0.03 s-1. The reduction in fracture energy in the constant case was greater. In both thermal conditions, fracture energy increased significantly when the strain rate increased from static (i.e. 10-5 s-1) to 0.03 s-1. In static loading conditions, fracture energy was approximately equal in both cyclic and constant thermal conditions. While in quasi-static strain rate (i.e. 0.03 s-1) Jci value of the solder joint exposed to cyclic temperature was almost 33% higher compared to the specimen that stored at constant temperature of 75℃. The average thickness of intermetallic compound (IMC) increased when the samples were placed at a cyclic and constant temperature. The average IMC thickness in a constant temperature state was about 17% larger than that in the thermal cycling state. Also, Cu6Sn5 and Cu3Sn phases were created in the solder layer of the specimen stored at a temperature of 75℃, but no phases formed in the sample experienced the thermal cyclic profile
  9. Keywords:
  10. Temperature ; Strain Rate ; Microstructure ; Solder Joints ; Fracture Surface ; Velative Humidity ; Cyclic Temperature

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