Multi-Condition Methodology for Stress Determination in the Reliability Assessment of Electrical Components

This paper presents an extended methodology for calculating Failure In Time (FIT) rates for automotive electronics, building upon Siemens Norm 29500. Many calculations rely on a single operating point, typically a worst-case scenario or an average value. For convex stress functions, a purely worst-case assumption can significantly overestimate the FIT rate, while using an average may lead to underestimation. The proposed approach incorporates multiple distinct operating conditions, each weighted by its respective share of operating time. A method for identifying and consolidating these different operating ranges based on analog sensor data is introduced. Mathematical analyses show that the resulting FIT rate can be lower than that obtained by a single worst-case value or higher than a simple average assumption, thus aligning more closely with real operating profiles. This provides significant potential for optimizing costs and development times without compromising the required safety standard.