Traditional metrology has been unable to adequately address the needs of emerging integrated circuits at the nano scale; thus, new metrology and techniques are needed. For example, the reliability challenges, and their root causes, in TSV enabled 3D-IC fabrication need to be well understood and controlled to enable mass production. This requires new approaches to the metrology. In this paper, we use microwave propagation characteristics (S-parameters) to study the thermo-mechanical reliability issues that precede electromigration failures in Cu-filled TSVs. The pre-failure insertion losses and group delay are reversibly dependent on both the device temperature and the amount of current forced through the devices under test. This is attributed to the plasticity of the copper fill in the TSVs.