Burn in
From Wikipedia, the free encyclopedia
- For the article on CRT burn in, see Phosphor burn-in.
Burn in is that process by which components of a system are exercised prior to being placed in service (and often, prior to the system being completely assembled from those components).
The intention is to detect those particular components that would fail as a result of infant mortality, that is, during the initial, high-failure rate portion of the bathtub curve of component reliability. If the burn in period is made sufficiently long (and, perhaps, artificially stressful), the system can then be trusted to be mostly free of further early failures once the burn in process is complete.
A precondition for a successful burn in is a bathtub-like failure rate, that is, there are noticeable early failures with a decreasing failure rate following that period. By stressing all devices for a certain burn in time the devices with the highest failure rate fail first and can be taken out of the cohort. The devices that survive the stress have a later position in the bathtub curve (with an appropriately-lower ongoing failure rate).
Thus by applying a burn in, early in-use system failures can be avoided at the expense (tradeoff) of a reduced yield caused by the burn-in process.
When the equivalent life time of the stress is extended into the increasing part bathtube-like failure rate, the positive effect of the burn in is inverted. In a mature production it is not easy to determine whether there is a decreasing failure rate. To determine the failure time distribution for a very low percentage of the production, one would have to destroy a very large number of devices.
When possible, it is better to eliminate the root cause of early failures than doing a burn in. Because of this, a process that initially uses burn in may eventually phase it out as the various root causes for failures are identified and eliminated.
For electronic components, burn in is frequently conducted at elevated temperature and perhaps elevated voltage. This process may also be called heat soaking. The components may be under continuous test or simply tested at the end of the burn in period.
