Constitutive equations for strain rate and temperature dependent mechanical behaviour of porous Ag-sintered joints in electronic packages

Sintering of silver attracts increasing attention in electronic packaging owing to superior bonding quality and high operation temperatures. However, the mechanical properties of sintered joints strongly depend on fabrication parameters like sintering temperature, pressure or organic solvents in the silver paste. In consequence, the mechanical characterization of this material is a challenging task. In the present article, unified constitutive equations for plasticity and creep of sintered silver are established. Thereby, particular interest is devoted to the influence of porosity on the mechanical properties. The assumptions of the model are validated by mechanical tests carried out with samples prepared under constant sintering conditions. The model parameters are fitted to test results performed in tension mode, in shear mode and under conditions of stress relaxation. This material model is implemented in the commercial software ABAQUS through user subroutines UMAT and VUMAT. In conclusion, the constitutive material model can be used as prerequisite for reliability predictions of Ag-sintered joints in electronic packages.