Shocks as Burn-in

As described in the previous chapters, in conventional burn-in, the main parameter of the burn-in procedure is its duration. However, in order to shorten the length of this procedure, burn-in is most often performed in an accelerated environment. This indicates that high environmental stress can be more effective in eliminating weak items from a population. In this case, obviously, the larger values of stress should correspond to the shorter duration of burn-in. By letting the stress to increase, we can end up (as some limit) with very short (negligible) durations, in other words, shocks. In practice, the most common types of shocks as a method of burn-in are “thermal shock” and “physical drop”. In these cases, the item is subjected to a very rapid cold-to-hot, or hot-to-cold, instantaneous thermal change or the item is dropped by a “drop tester” which is specifically designed to drop it without any rotational motion, to ensure the most rigorous impact. In this case, the stress level (to be called shock’s severity) can be a controllable parameter for the corresponding optimization, which in a loose sense is an analogue of the burn-in duration in accelerated burn-in.