Innovative methods for Burn-In related Stress Metrics Computation

Burn-In equipment provide both external and internal stress to the device under test. External stress, such as thermal stress, is provided by a climatic chamber or by socket-level local temperature forcing tools, and aims at aging the circuit material, while internal stress, such as electrical stress, consists in driving the circuit nodes to produce a high internal activity. To support internal stress, Burn-In test equipment is usually characterized by large memory capabilities required to store precomputed patterns that are then sequenced to the circuit inputs. Because of the increasing complexity and density of the new generations of SoCs, evaluating the effectiveness of the patterns applied to a Device under Test (DUT) through a simulation phase requires long periods of time. Moreover, topology-related considerations are becoming more and more important in modern high-density designs, so a way to include this information into the evaluation has to be devised. In this paper we show a feasible solution to this problem: the idea is to load in the DUT a pattern not by shifting inside of it a bit at a time but loading the entire pattern at once inside of it; this kind of procedure allows for conservative stress measures, thus it fits for stress analysis purposes. Moreover, a method to take the topology of the DUT into account when calculating the activity metrics is proposed, so to obtain stress metrics which can better represent the activity a circuit is subject to. An automotive chip accounting for about 20 million of gates is considered as a case of study. Resorting to it we show both the feasibility and the effectiveness of the proposed methodology.