Design And Property Study On A Sn-Ag-Cu Lead-free Solder Reinforced With Graphene

Among all the developed lead-free solders, Sn-Ag-Cu alloys have been widelyaccepted as the most promising lead-free solders because of their optimal mechanicalproperties and reliability. However, with the advancement of micro/nanosystemtechnologies, microelectronic devices have evolved to become smaller, lighter, andmore functional. Conventional lead-free solder technology may not guarantee therequired joint reliability in such cases. Hence, the development of new lead-freesolders is driven by the urgent requirements posed by the smaller, lighter, and morefunctional microelectronic devices.An attractive and potentially feasible method to enhance the performance of alead-free solder is to introduce reinforcements into a conventional alloy, so as to forma composite lead-free solder. In this study, the author attempt to introduce graphene asthe nano-reinforcement, which have superior thermal, electrical, and mechanicalproperties and can serve as an ideal reinforcement in electronic packaging material.This thesis mainly covers following two parts:First, varying weight fractions of graphene nanosheets (GNSs) were successfullyincorporated into lead-free solder using the powder metallurgy route, and the physical,thermal, and mechanical properties of the nanocomposite solder were characterized.With the increasing addition of graphene nanosheets, the nanocomposite soldersshowed a corresponding improvement in its wetting property but an insignificantchange in its melting point. The thermomechanical analysis showed that the presenceof graphene nanosheets can effectively decrease the coefficient of thermal expansion(CTE) of the nanocomposites. Furthermore, an improvement in UTS and a decrease inductility were recorded with the addition of graphene nanosheets.Then, The formation and growth kinetics of the intermetallic compounds (IMC)during the liquid–solid reactions and solid-state aging between composite solder andCu substrates were investigated, and the results were compared to the SAC/Cu system.Experimental results showed, during both liquid–solid reactions and solid-state aging,the interfacial IMC thickness of the unreinforced solder joints was observed to growfaster than that of the composite solder joints. Calculations suggest that the growthrate constant of composite is lower. It indicates that that the presence of a small amount of GNSs is effective in suppressing the growth of the overall IMC layer,which can prevent the IMC’s excessive growth and enhance solder joint’s reliability.