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Design, Fabrication and Characterization of Lead-Free Nano-Composite Solder Sn-Ag-Cu/ CeO2

Roshanghias, Ali | 2012

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 43183 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kokabi, Amir Hossein; Madaah Hosseini, Hamid Reza
  7. Abstract:
  8. As one of the key technologies for high performance electronic devices, composite solders have been recently developed to improve thermal and mechanical properties of solder joints. In this study, accumulative roll bonding (ARB) process was used as an effective alternative method for manufacturing high-strength, finely dispersed, void-free and highly uniform Sn-Ag-Cu/CeO2 nanocomposite solders. Microstructural investigation of nanocomposite solders revealed that homogenous distribution of CeO2 nanoparticle has been achieved and the eutectic as-cast morphology of the solder changed to recrystallized fine grained structure. As a result of severe plastic deformation during rolling, brittle and elongated intermetallics crushed into fine particles with an average diameter of a few hundred nanometers and dispersed uniformly in the solder matrix. Mechanical test results showed that the microhardness, 0.2YS, and UTS of the composite solder increased with addition of CeO2 nanoparticles, while the ductility of the composite was decreased. The creep resistance of the composites, characterized using a depth-sensing nano-indentation technique, increased with increasing volume fraction of CeO2 reinforcement. The values of the creep exponent suggested that the dominant creep deformation mechanisms involved were diffusion creep and grain boundary sliding. The interfacial evolution of nano CeO2 reinforced Sn-3.5Ag-0.7Cu composite solder on nickel-coated copper substrate was investigated during 100 °C and 150 °C isothermal aging up to 200 h. The results showed that growth of the (Ni,Cu)Sn intermetallic compound (IMC) layer was more suppressed with increasing volume fraction of CeO2 reinforcement. It was also found that the mean thickness of interfacial IMC layers increased linearly with the square root of the aging time. This relationship indicates that the growth of intermetallic compound is a diffusion-controlled process. The results also implied that the diffusion coefficients for composite solders were lower than those of monolithic one at both aging temperatures. The depressed growth of the IMC thickness in the composite solder joint can be attributed to an increased number of Ag3Sn particles adsorbed on the surface of IMC planes which reduce the interfacial energy of IMC layer. Furthermore, based on the results obtained in this study a solidification model for composite solder joint has been also developed. It was also found out the tensile strength of solder joint gradually increased with the increase of CeO2 weight percent, reached a peak value at 0.5 wt.% CeO2 and then decreased drastically with further increase of CeO2 content. Microstructural investigations of 1 wt.% CeO2 reinforced solder joint revealed that due to particle pushing under the influence of interfacial tension between the particles and the matrix upon solidification, the brittle clump-like layer with high concentration of CeO2 particles was formed inside the joint. This brittle clumps act as preferential sites for crack initiation during tensile test which would deteriorate the tensile strength. Hence, based on the results obtained in this study, addition of ceria particles up to 0.5 wt.% provide an optimized solder joint with improved strength together with suppressed IMC growth and long-term reliability
  9. Keywords:
  10. Nanocomposite ; Soldering ; Intermetallic Compounds ; Accumulative Roll Bonding (ARB) ; Metal Matrix Composite (MMC) ; Lead Free Solders

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  • طراحي، ساخت و مشخصه يابي لحيم نانوكامپوزيتي بدون سرب
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