Behind the “bathtub”-curve A new model and its consequences

The hitherto commonly accepted background model for the “bathtub” curve is rejected due to lack of experimental evidence. A new model — the S-curve model — based on bimodal or trimodal failure distribution functions and the concepts of “strong”, “freak” and “infant mortality” components is presented and its fitting with practical experience is demonstrated. The impact of the new model with regard to burn-in of components and systems and the use of reliability indicators to screen for built-in “flaws” in components are described.