Study Of The Interfacial Microstructure And Properties Of SAC0307-RE/Cu Solder Joints

In this paper, to find a kind of lead free solder that has both goodmechanical properties and technology properties is our final aim, and theinterfacial microstructure and properties of SAC0307-RE/Cu lead free solderjoints are studied. In our previous work, the effects of minimal rare earth (RE)element La additions on the microstructure of SAC solder joint, especially theintermetallic compounds (IMCs) under different aging time, were investigated.The results showed that the appropriate La content is0.07wt%.In the current study, the influences of Ce addition on the IMCs of SAC0307-0.07La/Cu solder joints were further talked about. The morphologies of IMCswere characterized by metallographic microscope (OM) and scanning electronmicroscope (SEM). Besides, the effects on the shear strength were examined byperforming the shear strength tests, while the hardness and the elastic modulus ofSAC0307-0.07La-xCe/Cu solder joints are characterized by nanoindentation.By the analysis and comparison of the interfacial IMCs of SAC0307-0.07La-xCe/Cu soldering joints reflowed(265℃) and aged(150℃) for differenttime, the conclusion is that the thicknesses of the IMCs increased by the parabolalaw with the increasing reflowing time and aging time respectively, while thethickness of IMC layer with0.05wt.%Ce is minimum. The morphology ofinterfacial IMCs changed from jagged to scallop-like. However, the interfacialIMCs become loosely because of the appearance of some voids.The results of shear strength test of SAC0307-0.07La-xCe/Cu solderingjoints indicated that the shear strength increased first but then decreased with theincreasing reflowing time, while it decreases with the increasing aging time. Themain fracture mode the soldering joints was ductile at the shear speed of0.05mm/s.0.05%.wt Ce addition can enhance the shear strength obviously. At last, the influence of Ce addition on the elastic modulus andmicrohadness is studied by nanoindentation. They both increase firstly and thendecrease with Ce content and reached peak values when Ce is0.05%.wt. Thehardness and elastic modulus of SAC0307-0.07La-0.05Ce/Cu solder joint bothdecrease with the increase of aging time.