Nanoindentation has been popular since the 1970s for querying material behavior at extremely small length scales. This paper focuses on using a combination of indentation and FEA methods for characterizing the viscoplastic behavior of composite materials and sintered materials, which pose additional challenges because of the heterogeneous morphology. In particular, this paper focuses on two forms of pressure-less sintered silver interconnect materials: an adhesive-based particulate composite for low temperature applications and a porous sintered version for high-temperature applications. By use of indentation methodology to bound the bulk viscoplastic properties for both of these heterogeneous morphologies, both sintered materials in this study are estimated to be less creep resistant than SAC 305 at operational stress levels, at room temperature.