| In electronic devices, a solder connection is used to provide the necessary mechanical integration and electrical connection between and within the various levels of an electronic package. With the miniaturization of devices, the electronic packaing technology is facing its limitations. There is an increasing urgency to develop new interconnection materials which are equipped with improved properties, so as to fulfill the ever-stricter service requirements. An effective way to enhance the performance of a conventional solder, is to intentional incorporate foreign phases into a conventional solder matrix, forming a composite solder. This thesis mainly covers the following aspects:1. Firstly, Ni coated carbon nanotubes (Ni-CNTs) reinforced 95.8Sn-3.5Ag-0.7Cu (SAC) solder alloy was synthesized using powder metallurgy route. The effects of Ni-CNTs on the physical, thermal mechanical properties and microstructure of SnAgCu solder materials were investigated. With the addition of increasing weight percentage of Ni-CNTs, the composite solder alloys showed a corresponding decrease in density values and wetting properties improved. The thermo-mechanical property results showed an increase in thermal stability in the composites. Mechanical properties characterization revealed an improvement of ultimate tensile strength and yield strength with lower weight percentages of Ni-CNTs (0.05%) incorporated and a reduction with higher weight percentages of Ni-CNTs (0.1%) .2. The creep behavior and hardness of SAC solder were studied using the Berkovich depth-sensing indentation at temperatures 25°C to 125°C. The results revealed that with increasing temperature, the creep penetration and steady state creep strain rate increased. Furthermore, the hardness results exhibited a decreasing trend as temperature increased. Then, nanoindentation studies of the SAC solder were conducted over a range of maximum loads. The indentation scale dependence of creep behavior and hardness were investigated. The results revealed that the creep rate, creep strain rate, indentation stress and hardness are all dependent on the indentation depth. At last, nanoindentation tests were performed on both composite and SAC solder samples to investigate their creep behaviour and hardness at room temperature. Characterization results revealed that with the addition of Ni-CNTs, the creep behaviour and hardness of composite solder improved significantly as compared to that of the unreinforced solder alloy. 3. Solid-state aging and thermal cycling aging studies were performed on small-size solder joints, to investigate the formation and growth of the intermetallic compound (IMC) at the solder/metallization interface. Shear tests were also conducted on as-soldered and aged solder joints. Results revealed that before and after aging, the interfacial IMC thickness of the unreinforced solder joints was observed to grow faster than that of the composite solder joints. Shear tests results revealed that as-soldered and aged composite solder joints had better shear strength than their monolithic counterparts and the shear strength of all aged solder joints decreased with increasing aging time/aging cycles.4. The constitutive behavior for creep performance of SAC solder joints was investigated. It was observed that the stress exponent (n) can be well-defined into two stress regimes: low stress and high stress. A new, improved constitutive model, which considered back stress, was proposed to describe the creep behavior of SAC solder joints. In this model, the back stress, which is a function of the applied shear stress in the low stress regime and a function of the particle size, volume fraction, coarsening of IMC particles in high stress regime, was introduced to construct the relationship between the creep strain rate and shear stress. It was demonstrated that the predicted strain rate-shear stress behavior employing the modified creep constitutive model which considered back stress, was in good agreement with the experimental results.
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