This section presents the last of the localized stress related problems discussed in this chapter. A discussion regarding the behavior and origin of the intrinsic stress is also initiated, but it will be covered in more detail in Chapter 6. In the last two sections, the impact of the intrinsic stress on the mechanical stability of the TSV became evident. The behavior and build-up of the intrinsic stress on a TSV’s metal layer during thermal cycling is investigated. The system is stressed beyond the elastic limit and a plastic model is required to describe the intrinsic stress evolution. In fact, this plastic deformation will ultimately lead to an overall strain (stress) relaxation, as will be explained later.