Highly Accelerated Life Testing (HALT) is an excellent and low cost approach for assessing the robustness of an electronic product; however, the potential variations in testing temperatures, vibration loads and shock prevent direct extrapolation of results to life data, precluding HALT from being a reliability predictor.
While amazingly powerful thermal tools can predict the distribution of junction, case and ambient temperatures in minute detail, it is often difficult to know what the temperatures should be instead of knowing what the temperatures will be. Even derating, the straightforward and long-held industry go-to methodology, cannot answer the “How hot is too hot?” question.
There are certain reliability tools available for thermal testing that have the ability to provide accurate predictions for even very complex thermal management solutions. But, they fall short of determining how hot is too hot for electrolytic capacitors.
Derating has always been a questionable practice, but it had some legitimacy in older electronics because solid-state mechanisms typically took decades to evolve and induce any significant number of failures.
Traditionally, determining appropriate component temperature was based on a combination of datasheet information and derating strategies. This method has since been proven outmoded since it does not factor in actual failure models and degradation mechanisms, resulting in expensive designs and/or products that lack optimum reliability.
Most electronics failures are due to thermal cycling, and are generally traced to two causes: circumferential cracking on the walls of plated through holes, and solder joint fatigue.
In our last article, we wrote about the basics of test plan development, and the value of defining test objectives, developing a justification checklist of specific test elements and identifying testing types and protocols.
Product test plans are critical to the success of a new product or technology, provided the tests are stressful enough to identify defects and correlate to a realistic environment so they are ultimately acceptable to management and customers.