Viscoplasticity Behavior of a Solder Joint on a Drilled Cu Pillar Bump Under Thermal Cycling Using FEA

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 both plastic strain and creep strain, as well as a submodeling technique to increase the accuracy of the analysis and decrease the analysis time. In addition, this study confirmed the superiority of the thermomechanical reliability of drilled Cu pillar bump through a hysteresis loop, which showed the equivalent stress versus equivalent inelastic strain of the solder joint interfaces. Moreover, the study compared the inelastic strain energy density values. The results demonstrated that the drilled copper pillar bump does indeed have a smaller inelastic range and a lower inelastic strain energy density.