Introduction
The reliability report is a summary of the test data collated since the
implementation of the reliability programme. This report will be periodically
updated typically on a quarterly basis. Future publications of this report will
also include as appropriate additional information to assist the user in the
interpretation of the data provided. The programme covers only IGBT /
CoPack manufactured products at IRGB, Holland Road, Oxted. The
reliability data provided in this report are for the package types TO247 and
TO220.
Further information regarding reliability data is available in the IR data book
IGBT-3, pages E-65-E-72. This also, is available from the Oxted office.
Reliability Engineering _____________________________________
Quality Manager
Date
_____________________________________
_____________________________________
IGBT / CoPack
Quarterly Reliability Report
Page 3 of 35
Fit Rate / Equivalent Device Hours
Traditionally, reliability results have been presented in terms of Mean-Time-To-Failure
or Median-Time-To-Failure. While these results have their value, they do not
necessarily tell the designer what he most needs to know. For example, the Median-
Time-To-Failure tells the engineer how long it will take for half a particular lot of
devices to fail. Clearly no designer wishes to have a 50% failure rate within a
reasonable equipment lifetime. Of greater interest, therefore, is the time to failure of a
much smaller percentage of devices say 1% or 0.1%. For example, in a given
application one failure per hundred units over five years is an acceptable failure rate
for the equipment, the designer knows that time to accumulate 1% failure of that
components per unit, then no more than 0.1% of the components may fail in five
years. Therefore, the IGBT / CoPack reliability or operating-life data is presented in
terms of the time it will take to produce a prescribed number of failures under given
operating conditions.
To obtain a perspective of failure rate from an example, let us assume that an
electronic system contains 1,000 semiconductor devices, and that it can tolerate 1%
system failures per month. The equation for the device failure is:
λ
= Proportion allowed system failures
Time period
In the case of the example,
λ
=
0.01 Failures
720 Hours
X
1
No. of devices
X
10
9
=
FITS
X
1
1000 Devices
=
10
9
=
14 FITS
or 14 FITs or 14 failures per 10
9
devices hours.
IGBT / CoPack
Quarterly Reliability Report
Page 5 of 35