| Abstract |
One of the major causes for field failure of DC-DC converters is the failure of power MOSFETs.
To cope with the fast advancement of the semiconductor technology and customers’ expectations
toward performance, service, delivery, quality, and reliability, it is necessary to identify defect
lots earlier in the production lines. For technologically advanced applications like power supplies
for servers, it is essential that only the best semiconductor devices are used to prevent failures and
as a result cut down on redundancy costs. Choosing power devices for converter applications has
been largely based on selecting the optimum voltage and current ratings and the lowest on
resistance of the devices. Blocking state leakage current limit of MOSFETs has never been a
criterion with designers. In this paper we show that screening MOSFETs for leakage current can
have a significant impact on the reliability of devices and hence on the DC-DC converter itself.
The time between failures is a very useful measurement to analyze reliability models for timedependent
systems. In many cases, the failure-generation process is assumed to be stationary,
even though the process changes its statistics as time elapses. This paper analyses the reasons for
failure of power MOSFETs in the useful life period of the device and based on a Weibull analysis
estimates the reliability of the devices and the probability of failures.
Weibull probability distribution efficiently maps the failures and it has been shown that it is
identical to the smallest extreme value distributions. Engineers at Pratt and Whitney have long
advocated that the Weibull method of failure estimation works very well even with extremely
small samples, even 2 or 3 failures. These methods of analysis can be applied to MOSFET
failures in DC-DC converters as well. |
