48 Improving reliability and quality for product success
In sum, because the lifetime of hardware is dened as the time at
which wear-out failure occurs intensively, it should be estimated only
by considering wear-out failures. Thus, the kinds of failure for a given
item should be analyzed, and random failure should be excluded in cal-
culating the lifetime. Note that wear-out failure mechanisms related
to lifetime are different from random failure mechanisms. Likewise, it
is necessary to distinguish the two kinds of failure mechanisms when
establishing test specications, as well as when analyzing failure data.
Short periods of testing under normal conditions may not precipitate
wear-out failure and t