Does building-in reliability imply more or less wafer-level reliability testing?

Wafer-level reliability (WLR) testing continues to be an important tool for implementing a building-in reliability (BIR) strategy. The thrust of WLR testing has shifted, however, from the back-of-the-line (monitoring of outgoing reliability levels) to the front-of-the-line (margin testing during the development and productization phase). The rapid nature of most WLR tests permits the process engineer to evaluate the impact of process variation and obtain an "almost instantaneous" feedback as to its reliability impact. Rapid reliability information feedback is a key to helping the process engineer to build reliability into the technology. This is extremely important today when technologies are being developed and introduced to fabs at a rapid rate.