Sequential stress combinations in product level reliability testing of industrial electronics

The reliability requirements for industrial electronics are high and in many cases electronics devices are used in harsh and varying conditions. To study the reliability of electronics in laboratory conditions accelerated life test methods are typically used. However, usually only one or two stresses are used in these studies even though electronics may encounter several sequential and simultaneous stresses during their lifetime. To achieve more accurate results or greater acceleration from the accelerated tests combinational testing methods are a good alternative to tests using only one stress. However, the knowledge about how different stresses affect each other is still highly unknown and this needs to be studied more. In this study the sequential combination effects of high temperature, high temperature high humidity, and temperature shock were studied using five different test sets. The studies showed that exposure to humid high temperature conditions had a greater effect on failure times in a temperature shock test than did dry elevated temperature. Moreover, the use of a temperature shock test prior to the high temperature high humidity test was found to accelerate certain failure modes. Consequently, such combinatory testing may be used as a highly accelerated test method for high reliability devices.