To estimate the life time of electronic products, several different characteristic quantities have to be extracted. However, the estimation has still a considerable variance because this measure evaluates the worst case only. The goal is to obtain the mean time to failure (MTTF) for standard operation conditions by extrapolations based on data of MTTF for elevated temperatures. To enforce a change of material properties, it requires a certain amount of external energy to cause harm to the device structure, if the energy exceeds a critical level.
The worst case for interconnect lines is a direct current, where the maximum of the electrical current density of a certain interconnect element is given by the approximation
There exist several additional constraints which affect the reliability of interconnect structures, such as the maximum allowed electric field for dielectric break down or the minium resistivity of the dielectric to limit leakage currents between different interconnect structures. However, these constraints are currently not of high interest because these requirements are just certain constraints of process technology nodes and can be taken into account in advance during the design phase.