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Due to miniaturization and high density of integrated circuits, bump solders are widely used in electronic industry for assembling electronic components on the connection of chip to substrate. Under the various operation conditions, solder bumps are subjected to cyclic stress and failed by thermal fatigue. To ensure the reliability of electronic products, it is becoming important to predict the fatigue failure of the solder bumps. In this study, effects of chip size on thermal fatigue life of the solder bumps were investigated by experiments and elastic-plastic finite element analysis, comparing four sizes of flip-chip devices to summarize the effect of chip sizes on temperature and stress/strain distribution, it turns out that strain/stress of corner bump was increasing with the chip size, at the end, we proposed a method to enhance the thermal fatigue life of solder bumps by using Parylene to protect the solder bump, results showed that Parylene layer could improve the strain and stress distribution significantly.

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 has reverse trend. 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. 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 different shear speeds.