CREEP FRACTURE BEHAVIOUR OF JOINTS SOLDERED BY A NANO-COMPOSITE SOLDER, LEAD-FREE AND CONVENTIONAL TIN-LEAD SOLDERS

摘要

Creep resistance and thermal fatigue performance of soldered connections/joints are essential reliability concerns for microelectronic, optoelectronic and photonic packaging systems. In this study, creep fracture behaviour of lap shear joints soldered by a tin-lead based composite solder reinforced by nano-sized metallic particles and a lead-free Sn-Ag-Bi alloy solder was characterized at different homologous temperatures, with a comparison to a traditional Sn60Pb40 solder. The results show that at all temperatures tested the nanocomposite solder has much better creep resistance than Sn60Pb40 solder, in terms of the creep rupture life. The lead-free Sn-Ag-Bi solder has superior creep performance to both Sn60Pb40 and nano-composite solders. The creep fractography analysis by SEM shows that a progressive shear deformation occurred as the main creep fracture mechanism. Sn60Pb solder joints deform dominantly by transgranular sliding, while Sn- Ag-Bi and nano-composite solder joints creep by intergranular mechanism through grain boundary sliding and voids growth. The mechanism of enhancing the creep resistance of nano-composite solder joints is that the nano-sized particulates with a uniform dispersion provide effective resistance by impeding grain boundary sliding and dislocation movement, besides the alloying effect of increasing elasticity modulus of the solder.