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Microstructure/Properties Relationship in Lead Free Solder Joint Reinforced with Graphene Nanosheets

Azghandirad, Sajjad | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54583 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kokabi, Amir Hossein; Movahedi, Mojtaba
  7. Abstract:
  8. Development of electronic industries, compression of electronic equipment, and removing lead from electronic circuits for environmental reasons, a significant challenge was created in the design and development of tin-based lead-free solders with physical and mechanical properties close to old tin-lead alloys. In this regard, the set of Sn-Ag-Cu alloys with eutectic composition and related compounds have been proposed as alloys to replace Sn-Pb solders. As a lead-free solder alloy, low melting point (≈217℃), high reliability of joints, and compatibility with various fluxes are among the properties of this category of alloys. In order to improve the mechanical properties of the joint resulting from soldering with these alloys, the composite process with different nanoparticles is used. In this study, a composite solder alloy with Sn0.3Ag0.7Cu compound reinforced with graphene nanosheets with different weight percentages (0, 0.05, 0.1, and 0.2) was used, and then flux was added. The microstructure of the alloys was investigated by scanning electron microscopy(SEM) and optical microscopy. Mechanical tests including nano-hardness and tensile-shear were performed to evaluate the mechanical properties of the joint. According to the results, by adding graphene nanosheets, the wetting angle of the solder first decreases and then increases. This parameter showed the optimal limit for solder samples containing 0.1% graphene nanosheets with a 10% reduction. The melting point and electrical resistance of the solder alloy did not change significantly with compositing. With the addition of graphene nanosheets, the thickness of the intermetallic compounds Cu6Sn5 present at the interface between copper and solder has been reduced by up to 30%. The presence of graphene nanosheets and the stabilization by the secondary phase deposition method in the grain boundaries, creating a fine-grained structure and reducing the thickness of the intermetallic compounds improved the hardness and joint strength by 20% for the optimal sample. The results of aging and thermal fatigue test for base solder alloy and nanocomposite solder alloy containing 0.1% graphene showed that the compositing decreasing the growth rate of IMCs thickness improves their morphology (from scallop shape to planar) and reduces the rate of decline of mechanical properties, which ultimately leads to improved joints properties and reliability
  9. Keywords:
  10. Lead Free Solders ; Intermetallic Compounds ; Joint Strength ; Thermal Fatigue ; Aging ; Graphene Nanosheets ; Tensile Strength Test ; Microhardness

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