Effects of bump size on deformation and fracture behavior of Sn3.0Ag0.5Cu/Cu solder joints during shear testing

To elaborate deformation and fracture behavior of Sn3.0Ag0.5Cu/Cu solder joint, dynamic shear testing was designed and performed on as-reflowed and aged solder joints which contained limited numbers of grains. Polarized light microscopy (PLM) and electron backscatter diffraction (EBSD) were used to reveal the grain morphology and the grain distribution. Scanning electron Microscopy (SEM) was applied to observe the influences of microstructures and intermetallic compounds (IMCs) on the solder joints fracture behavior. The experimental results suggested that the morphology and distribution of IMCs (Cu₆Sn₅ and Ag₃Sn) were the main reasons for the size effect in Sn3.0Ag0.5Cu solder joints. The shear strength of as-reflowed and aged solder joints decreased with the increased joint sizes. The nano-scale particle-like Ag₃Sn dispersed in the small solder joints had a strengthen effect on their mechanical property. While the dendritic and feather-like Ag₃Sn brought the big solder joints the brittleness. Furthermore, obvious plastic deformation in company with dynamic recovery and recrystallization was observed in small solder joints during dynamic shear testing. The fracture occurred in the bulk solder. While the brittle fracture occurred in big solder joints and the fracture positions were at the areas close to the soldering interface. The cracks propagated by the way of transgranular fracture. After aging, dynamic recovery and recrystallization occurred in all solder joints. While the plasticity of big solder joint was enhanced and the transgranular fracture as well as the intergranular fracture occurred during dynamic shear testing.