In this study, a multiscale thermo-mechanical analysis framework of die-attach solder material considering microscopic voids is proposed. Microscopic voids cause the degradation of solderability, thermal conductivity, electrical conductivity, and fatigue life. In spite of the significance of the issue, there has been no study on the efficient numerical analysis framework of thermo-mechanical behaviors of die-attach solder material including the small-sized microscopic void (< thickness of solder) as well as relatively large-sized microscopic void. Here, we focus on the effective thermal conductivity and thermal expansion efficient of the solder materials. Micromechanical approach is employed to develop the multiscale framework. In the presentation, the homogenized Anand viscoplastic model, which is widely employed in the thermal fatigue analysis, will be provided. It is expected that this work will be the foundation of the thermo-mechanical design of die-attach solder material.