|
Page 3 of 6 3. Analyze failures and separate them according to failure mechanism. All
failures must be analyzed in order to take corrective action. It is
truly amazing that many ESS operations do not include any structured
method to analyze the failures and to provide the results to those who
can take the proper corrective action. 4. Prepare plots of failure rate vs time for each failure mechanism. After
this is done, the criteria of Step 2 must be applied to each failure
mechanism. Again, only failure mechanisms with decreasing failure rates
can be attacked with ESS. 5. Improve the product. Without
using the data generated by ESS to improve the product, including
design, components, materials and processes, there is no hope of
reducing or eliminating the ESS process. If the staff responsible for
the ESS process is not the staff responsible for designing and
manufacturing the product, it is important that good communication take
place between the two groups. 6. Collect and analyze ESS data for the improved product. If
the proper steps have been taken to improve the product, then the area
under the infant-mortality region of the failure rate vs time curve
should be smaller. This may result from either a reduced slope of the
curve or from a shorter time in which it reaches a constant failure
rate. 7. Modify ESS conditions to reflect the new failure rates. As
failure mechanisms are eliminated, the stresses that precipitate them
may be eliminated. If they occur in shorter times, then the duration of
the ESS process may be shortened. In
some cases, additional stresses or increased levels may have to be
introduced to detect failure mechanisms which were not expected. If
this is the case, care must be taken to avoid introducing irrelevant
failures. 8. Reduce or eliminate ESS as warranted. If
the ESS process has been set up properly, and if the proper data is
collected and used effectively, it will result in a continuously
improving product. Eventually, a point will be reached where the ESS
process may be reduced significantly or eliminated entirely. It may
also be possible to reduce the frequency of ESS by going from a 100%
screen to a sample screen. The
effectiveness of ESS ultimately must be evaluated economically. This
analysis is based on the cost to conduct ESS, the cost of field
failures, and the frequency of occurrence of field failures.7,9,10,11,12,13,14
ESS costs include the cost of capital equipment, the recurring cost of
conducting the process, the cost of analyzing and repairing failures,
and the risk of actually introducing new failures into the product. The
benefit is in the reduced costs of field failures.
|
Support 
