Definition of "Initial Failure Rate"?

Question

Anyone please give a good definition for IFR? Thank you very very much...

Answer 1

I am not familiar with this term, so my answer may be way off. I assume that you are referring to the so called "bath tub" shaped curve of failure probability versas time with assemblies of components. Here, an assembly of components has a high probability of failure in its early life (the tap end of the bath-tub) due to faults in assembly, wrong components etc. Having passed this initial high probability of failure point, the assembly then settles down to a level section of the graph, and is the random component failure region. Here the probability of failure is low and is only due to odd rogue component failures. Finally, we reach the sloping section of the bath-tub, where the "wear-out" of components increases the probability of failure again.

I hope this helps.

Answer 2

"Initial Failure Rate"

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 bathtub-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.

Answer 3

Every electrical, electronic, and electromagnetic component has an initial failure rate associated with it. The number is usually empirically derived based on long time experience with the part-in-question, but sometimes manufacturers will perform special accelerated-life tests on components to more accurately determine the initial (base) failure rate.

The IFRs are given in units of failures per million hours, or FITs (failures per billions hours).

Manufacturers will publish IFRs for their parts on their websites. Sometimes you have to search a bit to find them. Sometimes they are listed as MTBFs (mean time before failure) which is the reciprocal of the IFR (per million hours). The military also has a published list of IFRs for military-quality (very high quality) parts in Mil-handbook 217. This standard is widely used in aerospace and (of course) military applications.

IFRs are statistical in nature. For example, the 'odds' of a resistor with a FIT of 0.1, failing after 10 billion hours, is 1 in 2. The odds of an LED with a FIT of 2000, failing after 500,000 hours, is 1 in 2.

Other factors such as high temperature, high stress (voltage, current, power), environment, and initial quality of the part, all add to the IFR. The IFR is that base failure rate of a part just 'sitting on the shelf' in a protected environment -- yes old, unused parts can just 'fail' on their own; it's rare but it happens.

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