Modification of Prony Series Coefficients to Account for Thermo-Oxidative Ageing Effects within Numerical Simulations

Ageing effects potentially limit the lifetime of electronic device and systems. To prevent failure during the desired lifetime, knowledge about the used materials is of key importance. Moreover, the change of the used materials during the expected lifetime and its impact on the functionality of the product needs to be considered.In this study, a simulation approach is discussed that can consider ageing effects caused by oxidation at elevated temperature of a printed circuit board material used for radio-frequency applications. By state-of-the-art thermomechanical material characterization, the properties are derived of samples that were stored at elevated temperature (175°C) for up to 1000 hours.Within the simulation workflow, the properties of the different aged states are defined by modifying the pristine properties. Four exponential functions are derived modifying the initial modulus, the characteristic time constants, the shift function and the coefficient of thermal expansion, all in dependency of ageing time.This new approach is compared with an approach where for each aged state a different material set is defined. The deviation between experiment and simulation becomes larger with this new approach, which was expected, since much less detailed information about the material properties are being used. However, the new approach has a major benefit of opening up the opportunity to, for example, perform sensitivity analyses in a very simple manner. Additional benefits are the gained knowledge on how the material is changing over time and the possibility to extract material properties for aged times that are not being measured.