Off the bathtub onto the roller-coaster curve [electronic equipment failure]

In 1981 it was revealed that the instantaneous failure rate of a piece of electronic equipment decreases with age during its useful life and that the bathtub characteristic for hazard rate is an exception rather than the rule. The shape of the hazard rate curve for this device is studied by the authors. Investigators studying semiconducting device burn-in subscribe to the concept of freak failures which manifest themselves as a hump on the hazard rate curve. The authors call these curves the roller-coaster curves. It was postulated that aside from the long-term gross wear-out failures, all other failures develop from flaws. With some general assumptions on the flaw size distribution, one can show (by applying fatigue theory) that the flaws would emerge as failures that give a decreasing failure rate