Creep properties of microscale lead-free solder joints with different volumes

Adopting accurate creep testing method based on dynamic mechanical analyzer (DMA Q800, TA-Instruments),high temperature creep mechanical behaviors and properties of lead-free Sn-3.0Ag-0.5Cu microscale solder joints with volumes of 5.34×10⁷ μm³ and 7.07×10⁶ μm³ were investigated under two different service conditions. One condition was keeping the tensile stress (20 MPa) constant at four different temperatures (100,125,135,and 145℃), and the other was keeping the temperature (145℃) constant under four different tensile stresses (8,12,16,and 20 MPa). The experimental results show that all strain-time creep curves of microscale solder joints included three typical stages-primary creep,secondary creep (steady creep) and tertiary creep. Also, the creep activation energy and creep stress exponent value were very close to each other, though the volumes of the Sn-based solder joints were obviously different, this was mainly because the lattice diffusion was thought as the creep mechanism during the high temperature creep process. In addition, under the same testing temperature and same loading stress, the steady creep rate of the Sn-3.OAg-0.5Cu microscale solder joints with large volume was much higher than that of the smaller ones, however, the creep lifetime had totally opposite trends due to more defects in the larger solder joints.