Parametric Reliability Analysis In DfRSoft
Parametric Reliability Analysis
Exclusive
from DfRSoft  Parametric Reliability Analysis.
Assess device degradation failure rates over time without having
to test to failure and with more accuracy saving hours of test
time, at lower stress and with smaller sample sizes. Here is
how:
There are three ways to assess the failure rate of a
device that drifts out of specification. As an example we will
do Power loss for a device.
Each way requires a Parameter Limit, such as Power Limit. Let
say 20% Power loss.
Method 1: Consider a power limit of 20%. Devices are on life
test and when they reach 20% Power Loss, this is treated as the
time to failure. In this method a catastrophic analysis is used.
Use for example the Rel plts page to do a Weibull assessment.
Put the times to failure for each device and perform the
analysis similar to catastrophic data analysis. In some cases
this may be the best method when an aging law is not known.
Method 2: Initial and Final Parametric Measurement Method:
In this method we require less test samples since we can
characterize the devices distribution with say 20 or 30 samples.
Typically device may be on life test at an elevated temperature
and we simply take two measurements at room temperature  before
and after the test. We have a population of samples and we find
its mean and sigma. At this point we can use the parametric
method where we can often prove a more accurate failure rate at
a specific confidence level than say a catastrophic analysis,
even when no failures occur. In addition we can get a point
estimate (i.e., no confidence bound data estimate) which cannot
be done when 0 failures occurs in the catastrophic analysis
method. To do this follow the hyperlink below for Initial and
Final drift measurement analysis.
Method 3: In this method, if a general aging model is known i.e.
how the drift for power loss occurs over time, then Parametric
reliability analysis makes the most sense and has tremendous
advantages over Method 1 & 2.
For example, the three aging laws in DfRSoft are:
Parameter Shift=A (Time)^B ,
Parameter Shift = A Log(1+B Time)
or Parameter Shift = User defined.
DfRSoft allows time to be accelerated with an
acceleration factor. An Arrhenius calculator is available to
determine this factor if temperature is the acceleration stress.
METHOD 3 ADVANTAGES:
If the Aging Law is known then there are three major advantages
over Method 1:
1. We require less test samples since we can characterize the
devices distribution with say 20 or 30 samples.
2. We do not have to test to failure only over a sufficient time
to fit the data to the aging law. With knowledge of the ageing
law and its distribution, the reliability can quickly be
predicted at any temperature.
3. We can test at a lower stress like a lower temperature since
we do not have to test to failure. Often the closer the
temperature to the use conditions for example, the more accurate
will be the prediction to the extrapolated temperature of
interest.
SEE
DfRSoft PARAMETRIC RELIABILITY INSTRUCTIONAL VIDEO
