Parametric failure rate model for quartz crystal aging/reliability of surface acoustic wave filters.

A theoretical model for the predictions of parametric failure rates of quartz crystal devices is obtained. The model is based on a commonly used aging law for quartz acoustic wave devices. To use the model it is only necessary to statistically characterize the parameter's distribution for the devices at two different times and define a parametric failure limit. An example is given in which a representative sample lot of 30 surface acoustic wave filters is used to characterize the frequency and phase of the population at two different times under accelerated stress conditions. Using these results for the representative lot, the model predicts the cumulative percentage of the population which would fail as a function of time in the field, and the cumulative and instantaneous failure rate in time at use conditions. These predictions are based on defined limits for parametric stability. Such requirements are generally defined by the customer's needs. General results of the model show that when a characteristic parameter of the population being investigated is distributed in Gaussian form, and ages according to the assumed crystal aging law, then the failure rate is lognormal in time. The concepts of the model are, straightforward, and the methodology may be applied whenever a device's aging law is known.