Assessing Product Reliability
8.1.5. What are some common acceleration models?
|The Arrhenius model predicts failure acceleration due to temperature increase||
One of the earliest and most successful acceleration models predicts how time-to-fail varies with temperature. This empirically based model is known as the Arrhenius equation. It takes the form
|The Arrhenius activation energy, H, is all you need to know to calculate temperature acceleration||The value of H
depends on the failure mechanism and the materials involved, and typically
ranges from .3 or .4 up to 1.5, or even higher. Acceleration factors between
two temperatures increase exponentially as H
The acceleration factor between a higher temperature T2 and a lower temperature T1 is given by
Using the value of k given above, this can be written in terms of T in degrees Celsius as
Note that the only unknown parameter in this formula is H.
Example: The acceleration factor between 25°C and 125°C is 133 if H = .5 and 17,597 if H = 1.0.
The Arrhenius model has been used successfully for failure mechanisms that depend on chemical reactions, diffusion processes or migration processes. This covers many of the non mechanical (or non material fatigue) failure modes that cause electronic equipment failure.