Accelerated tests are typically used to find and identify potential failure mechanisms in semiconductor
devices and to estimate the rate of their occurrence in electronic systems. The historical approach to
investigating the relationship between a maximum stress failure rate and a system failure rate is to
choose a single representative "equivalent" thermal activation energy for a given product or product
group. A single, best-estimate activation energy value facilitates accurate estimation of the acceleration
factor for the device failure-rate estimation in the system application. While that approach has been
generally accepted by the industry because of its simplicity and direct relationship to products, another
method has been developed, the Sum-of-the-Failure-Rates method, that offers more knowledge of why
devices fail.