Selecting the Correct Accelerated Life Model

Adam Bahret

This presentation will review methods for correctly selecting an ALT model based on identification of the primary wear-out failure mode and it’s underlying “Physics of Failure” (POF). One of the largest challenges in creating an accelerated reliability test is correctly identifying the POF. This POF is the foundation in selecting an acceleration model. Far too often a program goes down a path based on an acceleration model that is not related to the primary, wear-out failure mode that drives end of life. A common example is selecting the Arrhenius acceleration model for a PCB life test without investigating if the primary wear-out failure mode is from material degradation. The Arrhenius model is based on the physics of failure that the wear-out is driven by material degradation due to interaction with another element, oxygen, salt, etc, and can be modeled accurately using thermal input as the acceleration variable. But it may in fact be that the primary wear-out failure mode is from thermal expansion and contraction creating a gap in the enclosure seal which permits water ingression and corrosion. The correct model in this case would have been the Coffin Manson model which uses range of temperature delta as the POF acceleration factor. Including a standardized methodology in your engineering best practices that includes this analysis and validation in an ALT program will ensure accurate prediction of your product end of life characteristics.