Loading...

Fabrication and Characterization of Lead-free Nanocomposite Solder Reinforced with Magnetic Coated Graphene NanoSheets (GNSs)

Tamizi, Moein | 2024

0 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 57081 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Movahedi, Mojtaba; Kokabi, Amir Hossein
  7. Abstract:
  8. In this study, by adding graphene/cobalt reinforcement particles (CoGNSs) to lead-free low-silver SAC0307 solder, an attempt was made to improve the physical, metallurgical, and mechanical properties of the composite soft solder during the reflow soldering process. Additionally, the effect of applying a pulsed magnetic field on controlling the arrangement and distribution of graphene/cobalt particles in the solder matrix during the melting and solidification process in the reflow soldering process was evaluated. A composite solder paste was prepared by adding 0.05, 0.1, 0.2, and 0.5 wt% of graphene/cobalt particles to the lead-free low-silver SAC0307 solder powder, along with a rosin mildly active (RMA) flux, using the mechanical mixing method. Subsequently, the physical, metallurgical, and mechanical characteristics of the composite solder alloy were investigated, both soldered with a copper substrate and under aging conditions at 110°C for durations ranging from 50 to 1000 hours. The results of the viscoelastic behavior of the solder paste in the soldering temperature range showed that the presence of cobalt coating on the surface of graphene particles improved the viscosity coefficient compared to graphene particles without coating by up to twice. Additionally, the wettability and spreading properties of the composite solder alloy were enhanced through the mechanism of reactive wetting and absorption theory, and the contact angle of the composite alloy containing 0.1 wt% graphene/cobalt decreased by 48% to 11.5° at 270°C. The physical properties of the composite alloy indicated that parameters such as melting temperature, soldering temperature range, and electrical resistance did not change significantly with the composite process. The amount of undercooling was decreased by the addition of graphene/cobalt particles up to 0.2 wt%, indicating the nucleation-promoting role of the particles. The application of a pulsed magnetic field during reflow soldering resulted in grain refinement, increased high-angle grain boundaries, and decreased intensity of the preferred rapid growth direction of <110> Sn in the base solder alloy. Additionally, in composite solder alloys, the magnetic field led to an increase in volume fraction and more uniform distribution of CoGNSs particles in the matrix, causing the CoGNSs particles to play a greater role in the formation reactions of the Cu6Sn5 and Ag3Sn, leading to increased volume fraction, reduced size, and alignment along the direction of the magnetic field. The minimum thickness and grain size of the intermetallic compound phase (Cu,Co)6Sn5 were achieved for the composite solder alloy containing 0.1 wt% graphene/cobalt with the application of a magnetic field during reflow soldering. EBSD results indicated that the application of a magnetic field affects the density of low-angle and high-angle grain boundaries, the cyclic six-fold twin growth model [010]{301} of Sn in the presence of graphene/cobalt particles, and the solder's anisotropic behavior. Maximum hardness, elastic modulus, creep resistance, and shear strength in the tensile-shear test were obtained for the composite solder alloy with the optimal amount of reinforcing particles of 0.1 wt% graphene/cobalt with the application of a magnetic field during reflow soldering. In the nano-indentation creep test, the creep strain rate decreased from 3.4 ×10-4 1/s for the base alloy to 3.8 ×10-5 1/s for the composite solder alloy containing 0.1 wt% graphene/cobalt. Furthermore, a mechanism of dislocation climb and glide for the creep of composite solder alloys was proposed based on the power law creep equation. During aging at 110°C for the composite solder alloy containing graphene/cobalt, the growth kinetics of the common intermetallic compound (Cu,Co)6Sn5 relative to Cu6Sn5 in the base alloy decreased. The application of a magnetic field controlled the distribution of graphene/cobalt reinforcement particles on the surface of the common intermetallic compounds and the alloy matrix, affecting the diffusion phenomenon and the diffusion path of cobalt during aging. During aging, the phenomena of recrystallization and grain growth were observed at times of 320 hours and 1000 hours, respectively
  9. Keywords:
  10. Mechanical Properties ; Physical Properties ; Microstructure ; Reflow Process ; Lead Free Solders ; Pulsed Magnetic Field ; Composite Lead-Free Solder ; Reflow Soldering Process ; Graphene/Cobalt Particles

 Digital Object List

 Bookmark

No TOC