With the size of Lead-free solder joint decreasing, the reliability of solder joint is particularly prominent, which the mechanical properties of solder joint are critical to its reliability. Meso-mechanical properties and creep behavior of the SAC0307-xCe/Cu micro-solder joints were studied by Berkovich nanoindentation tests with different loading rates at room temperature. The load-depth curves were rate dependent. As the rate increased, the creep depth was increased at same hold time. The Young's modulus of SAC0307-xCe/Cu solder joints are 46.9±0.9 GPa, 50.3±1.0 GPa, 51.4±0.8 GPa and 52.5±1.1 GPa, respectively, and indention hardness are 151.37±3.25 N/mm2, 152.85±2.96 N/mm2, 156.79±3.06 N/mm2, and 167.33±3.58 N/mm2, respectively. It can be seen that Young's modulus and indention hardness increase with the increasing of Ce content. The strain rate sensitivity of creep m was fitted linearly by analysis of Anti-Physics of indentation hardness Hcr and strain rate έ cr of creep. The stress index of creep n was calculated. The m values are 0.3944, 0.3229, 0.2029, 0.1233 respeetively and the n values are 2.5355, 3.0969, 4.9285, 8.1103 respeetively on SAC0307-xCe/Cu micro-solder joints, with the increasing of Ce content, the creep resistance property of SAC0307-xCe solder joints has changed much, m decreased and n increased. Results shows that adding trace amounts of Ce elements into low-Ag solder have notable effort to improve the meso-mechanical properties and creep resistance, Ce element will play an important role in providing better electronic interconnections.

The reliability of SAC lead-free solder joints are believed to be greatly influenced by the interfacial intermetallic compounds (IMCs) between solders and substrates. Our previous works investigated the effects of minimal rare earth (RE) elements addition on the interfacial IMCs under different aging time. Experimental results showed that the appropriate RE content is 0.07wt% La in Sn-0.3Ag-0.7Cu (SAC0307). In this paper, the influences of reflow parameters and Ce addition on the IMCs of SAC0307-0.07La/Cu solder joints were studied. The morphologies of IMCs were characterized by metallographic microscope (OM) and scanning electron microscope (SEM). Besides, the shear strength of the solder joints was evaluated by the shear tests. In comparison purpose, all the solder balls were prepared under the same conditions. The results showed that the thicknesses of the IMCs increased following the linear law and the shear strength varied under the parabolic law with the increase of reflow time. Meanwhile, the shear strength of the solder joints increased almost linearly with the increase of the cooling rate. The main failure mode was ductile fracture when the shear speed was 0.05mm/s.

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