IGBT Modules - Technologies, Driver and Application (Second Edition) - page 499

14 Qualityand reliability
14.1 Introduction
The quality and reliability of power devices are of high priority. This is essentially based
on the fact that the devices are often used in exposed and/or critical (sometimes even
life-critical) applications. Further, the fact that the power semiconductors will play a
significant part in the application cost. Therefore, manufacturers carry out extensive
testing and qualification programs, in order to meet the expectations of the users of
such components.
On the other hand, it is the responsibility of the designer to select suitable components
for each application. Manufacturers provide a variety of tools and data with which a
reasonable estimate of the operational capability and service life of a component in the
application can be achieved. The goal of any "good" design should be to calculate for a
lifetime longer than the customer expects and extend the design criteria beyond the
specification. This then results in a so-called robust design as depicted i
Fig. 14.1
Robustness of a design
A failure is defined as total or partial loss of function of a component which, at the
beginning of the operational exposure, could be classified as to be free from defects. In
general, two types of failures can be distinguished: Sudden failure and drift failure.With
sudden failure, the failure may occur at any time and is not predictable. Drift failures
occur, however, due to a gradual change of state. The time of failure can be predicted in
principle. A limit must be set, beyond which the component is considered as to have
14.1.1Failure rate, FIT, MTBF andppm
The failure rate
is defined as the total number of defects n of a certain number of
components N during the time
t. The failure rate for components is normalised to one
failure per one billion device-hours and is quoted in the unit of FIT, which stands for
"Failure inTime".
Eq. 14.1
1...,489,490,491,492,493,494,495,496,497,498 500,501,502,503,504,505,506,507,508,509,...548
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