Effect of solder volume on shear strength of Sn-3.0Ag-0.5Cu solder and Cu metallization

Shear behavior of Sn-3.0Ag-0.5Cu solder joints on ball grid array substrates was investigated with different solder volumes and shear speeds to study the solder volume effect on shear properties. Both solder volume and shear speed were found to have strong effect on the shear strength. The shear force decreases obviously with the decrease of the solder volume due to the significant decrease of loaded area, while the shear strength increases sharply with the decrease of solder volume as a result of the discrepancy of interfacial reaction and microstructure. And the shear strength increases rapidly with the increase in shear speed due to the limited grain boundaries or interphase boundaries sliding and dislocation movement and the shear speed has stronger effect on the small solder joints. After the shear test, fracture surfaces were investigated by canning electron microscopy equipped with energy dispersed x ray and it was found that the fracture mode of as-reflowed solder joints was primary ball cut within the bulk solder near the interface with a ductile rupture. The results suggest that even if the solder shear tests showed the same fracture mechanism, solder volume still has great effect on the shear properties at each different shear speed.