Reflow of Sn-rich solders on a Cu substrate results in the formation of several Cu-Sn and Ag-Sn intermetallics, which control the properties of the solder joint. Bulk measurement of physical properties, such as Young's modulus, is problematic and may be affected by porosity and undesired phases. In this paper, we report on the accurate and reliable Young's modulus values of Cu 6 Sn 5 , Cu 3 Sn, and Ag 3 Sn intermetallics, measured in situ in a solder joint by nanoindentation. The measured values for Cu 6 Sn 5 , Cu 3 Sn, and Ag 3 Sn, were 112.3+/-5.0, 134.2+/-6.7, and 78.9+/-3.7GPa, respectively. Comparison of these values with limited data in the literature was also conducted and is discussed.