Accelerated Life Test
An accelerated life test is a method of observing long-term wear behaviour in a short time by running the product under harsher temperature and cycling conditions than normal use. The result is not a definite lifetime figure, but an early indication of which component is the weak link.
The idea the method rests on is that many wear mechanisms accelerate with temperature. The drying out of electrolytic capacitors, the fatigue of solder joints and the degradation of insulating materials fall into this group; as temperature rises, the same degradation occurs in a shorter time.
- What is learned: the first component to degrade and the symptom of the degradation. This information turns directly into a design decision: a part of a higher temperature class, a larger cooling area or a lower current target.
- What is not learned: the real number of years in the field. Acceleration factors rest on assumptions and vary from mechanism to mechanism.
- Limit of application: a stress exceeding the absolute limits of the components produces a degradation mode that will never be seen in the field and makes the result meaningless.
On products such as motor drivers and control boards, this test is generally carried out by applying temperature cycling together with load cycling; this way both electrical and thermal fatigue are monitored on the same sample.
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