The electronic packaging industry has moved from eutectic Sn-Pb solder materials to near-eutectic SnAgCu (SAC) solder materials in the past decade because of the increasing awareness of health and safety concerns associated with the use of Lead (Pb). The reliability performances for SAC solder materials under thermal and isothermal aging conditions have been extensively studied and results show aging is universally detrimental to the solder joints reliability, which leads to a large degradation of mechanical properties including tensile strength, shear strength, and fatigue behaviors. Moreover, solder joints in realistic applications are typically exposed to cyclic loading, either through thermal cycling or mechanical cycling. Numerous solutions have been proposed to mitigate the aging-induced or cyclic-induced mechanical properties degradation. One of the possible solutions is to develop “next generation” solder alloys with additional elements mixed with SAC solder alloys. This process is called solder doping. Common solder dopants include nickel (Ni), bismuth (Bi), antimony (Sb), and indium (In). Solder doping was observed to have a substantial influence on mechanical properties of solder joints, such as an increase of solder ultimate tensile strength and shear strength. However, as bulk sample has been used in decades in testing the mechanical properties of solder materials, studies have revealed that mechanical properties exacted from bulk sample may not be the real reflection of solder joints implemented in the realistic application, since the solder joint was proved to demonstrate a much more complex structure than bulk sample. Therefore, in this study, solder joints assembled on the PCB were used directly as test specimens, where several important factors that may have critical impacts on solder joint reliability can be tested, for example, intermetallic compound (IMC) and surface plating (surface finish). The purpose of this dissertation is to study several impact factors (aging, surface finish, solder doping, IMC) on the reliability of solder joints under realistic applications.