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Although the copper (Cu) pillar bump (CPB) was developed in accordance with recent trends of miniaturized, multifunctional and high-performance technology, its thermomechanical reliability remains in question. Accordingly, a hole was drilled into a CPB to increase its thermomechanical reliability, and the viscoplasticity behaviors of the two structures were subsequently compared through finite element analysis. In particular, this study applied the Anand model, which addresses plastic strain and creep strain, as well as a submodeling technique to increase accuracy of the analysis and decrease analysis time. This study confirmed the superiority of the thermomechanical reliability of drilled copper pillar bump through a hysteresis loop, which showed the equivalent stress versus equivalent inelastic strain of the solder joint interfaces. Moreover, the study compared inelastic strain energy density values. The results demonstrated the drilled copper pillar bump does indeed have a smaller inelastic range and a lower inelastic strain energy density. (Journal of Electronic Materials, February 2017, vol. 46, no. 2), Bang; [...]