Event-based use conditions method for thermo-mechanical reliability risk assessment

The traditional approach of thermo-mechanical (T-M) reliability modeling is based on power cycle events. This approach is not useful for products which are rarely powered down, because power cycles alone do not capture all the reliability stress from temperature variation over these products´ use life. This paper describes a methodology to determine the temperature cycle requirements for products like smartphones and tablets which accounts for the temperature variation associated with usage events, which we call “mini-cycles”. The T-M model is based on the distribution of individual users´ histories as a series of events over time, which is then translated into a temperature vs. time trace for each user. These temperature traces are then used as the main inputs to T-M models, for example using the Norris-Landzberg (N-L) acceleration model to evaluate solder damage for each user. Results are summarized in a distribution of T-M damage across all users. This new methodology improves the understanding of thermo-mechanical reliability requirements due to the impact of “mini-cycles”.