Reliability is a measure of the ability of a solid state product to continue to meet data sheet
specifications over time. In any population of solid state products there is a range in the time to failure, which
is the time-to-failure distribution. Since the typical time-to-failure distribution will have a central
characteristic in the order of hundreds or thousands of years, means must be derived to assess the
time-to-failure distribution in real time. Failure mechanism models provide a physical and
mathematical representation of how the time-to-failure distribution will change by changing some
factor.