Abstract
In the solder interconnect technology of flip chip bonding, a thin intermetallic compound layer is likely to form at the interface between solder bump and under bump metallurgy due to the constitutional chemical diffusion. Generally, the shear strength of the intermetallic compound is less than that of the solder. This would influence the drop impact reliability of the solder bump. In addition, as the thickness of intermetallic compound is up to a certain value, a high local stress would commonly occurred at the interface between intermetallic compound layer and its neighborhood, thereby leading to the crack formation and solder bump failure. Thus, it is essential to explore the mechanical property and behavior of intermetallic compound for improving the reliability of the solder bump. Up to date, though the mechanical properties, such as hardness and Young’s modulus, of the intermetallic compound can be measured through the nanoindentation, it is hard to accurately grasp the elasto-plastic behavior of intermetallic compound, i.e., strain hardening exponent and yield stress and, etc., due to the constrains of nano/micro samples fabrication of intermetallic compound and measurement technique. Therefore, the numerical calculation could be the alternative method, which is in replacement of experimental approach, to obtain the mechanical property and behavior of intermetallic compound. Though the Dao model can yield the elasto-plastic behavior, i.e., strain hardening exponent and yielding strength, of the material, whose Young’s modulus is in the range of 10~210 GPa. Nevertheless, the range of the Young’s modulus of the material investigated in the Dao model is extremely extensive. It would result in a lack of the data regarding to development of the Dao model, thereby resulting in a substantially error for Dao model in prediction of elasto-plastic behavior. This thesis constructed the material property and relationship of nanoindentation empiric parameter of the intermetallic compound (Young’s modulus is in the range of 60 ~ 200GPa) by mainly modifying the Dao model to further investigate the elasto-plastic behavior of intermetallic compound. According to the experimental and simulated results, the ratio of initial unloading stiffness and reduced young’s modulus of the intermetallic compound was not constant, and it would vary with different material. This thesis successfully established the relationship between the ratio and nanoindentation empiric parameter. Thus, the strain hardening exponent and yield stress of intermetallic compound were effectively evaluated. Finally, this thesis applied the modified Dao’s material analysis model together with Coffin-Manson fatigue life empiric formula to further investigate the elasto-plastic behavior effect of intermetallic compound on the reliability of SnAg solder bump of the high-density and ultra-fine-pitch 3D chip-on-chip stacking packaging under accelerated thermal cycling loading. The calculated results reveal that the accuracy of prediction of solder bump reliability can be significantly enhanced as the elasto-plastic behavior of the intermetallic compound is taken into account.