Relative effectiveness of thermal cycling versus burn-in: a case study

In environmental stress testing (EST) programs for various types of communications equipment, two experiments were conducted to gauge the relative effectiveness of thermal cycling and burn-in for a typical communications system which uses optical transmission. The first EST regimen was a series of thermal cycles (A) followed by an extended period of burn-in (B). This order was reversed in the second EST regimen which consisted of (B) followed by (A). By comparing the failure distributions in time for the AB and BA experiments, one can discern the relative effectiveness of the thermal cycling and burn-in for stimulating failures. The results clearly show that thermal cycling reveals important failure modes which are not effectively precipitated by burn-in alone. Some of these failures occur as intermittent failures during the temperature transients. Moreover, thermal cycling does tend to reveal many of the same failure modes precipitated by burn-in because the thermocyclic test regimen inherently involves successive time intervals at elevated temperature. On the other hand, the data suggest that time-at-temperature (burn-in) failures are also involved. Therefore, a balanced test regimen of thermal cycling and burn-in seems advisable