Forum: Reliability & Maintainability Questions and Answers

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Posted by: Kevin
Date posted: Mon Sep 9 13:09:24 US/Eastern 2002
Subject: MOSFET Derating
Message:
We have a power MOSFET transistor (LDMOS), to be used in a ground benign environment, that we're derating from 200C to 150C. This FET can experience rapid changes in its output power and so will see significant thermal cycling. Is there any information on the reliability impact of thermal cycling on these devices and would this make us want to derate the device further? D-RATE doesn't seem to address this.

Replies:
Power Transistor Cycling
B.W.Dudley Tue Sep 10 13:45:44 US/Eastern 2002

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Posted by: Ken
Date posted: Mon Sep 9 7:51:02 US/Eastern 2002
Subject: EQT
Message:
I'm currently facing a problem in Environmental Testing. I wanted to conduct a humidity test to qualify for the driver instrumental panel of an army vehicle. How many cycles should i specify to my contractor to get a pretty accurate results? Do we specify the number of cycles based on the usage profile? Mil-810E doesn't taught us how to specify number of cycles. Theoretically, does passing EQT for humidity guarantee that it's free from humidity problem for it's entire life cycle?

Replies:
Environmental Testing
B.W.Dudley Mon Sep 9 9:29:16 US/Eastern 2002

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Posted by: Wayne
Date posted: Sat Sep 7 6:22:22 US/Eastern 2002
Subject: Chargeability of failures
Message:
What i mean is during the course of testing contractors are unable to retify the problem due to the complexity of the problem and to avoid delaying the schedule, it has been agreed on both sides to continue testing. However the same failures occurs a few times till the end of the test. Is it fair for us to charge them for the total number of failure times or just once?

Replies:
Fair and Foul
BWD Mon Sep 9 9:54:01 US/Eastern 2002

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Posted by: Wayne
Date posted: Thu Sep 5 22:25:54 US/Eastern 2002
Subject: AMSAA valid?
Message:
experience a problem when using the AMSAA model that is my Instantaneous MTBF is higher than my test duration. For e.g i test for a duration of 1000hrs with only 2 failures that occur in the very beginning of the test. Based on this set of data i use the AMSAA Model and the Instantaneous MTBF m(t) of about 1500, which is HIGHER than my test duration. Why is it so? I thought that MTBF cannot exceed the number of test hours. Can enlighten? Is the m(t) a accurate representation of the system at the end of RDGT?

Replies:
Reliability Growth
Patrick Hetherington Fri Sep 6 6:34:19 US/Eastern 2002

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Posted by: Wayne
Date posted: Thu Sep 5 9:31:12 US/Eastern 2002
Subject: Chargeability of faliures
Message:
If a failure occurs in the midst of testing and no corrective actions are carried out and the SAME failure reoccur several more times. In this case do we charge the failure once or multiple times? Contractors could not retify the failures due to lack of time and to avoid delaying the whole program. Does Mil-Std state clearly that we could charge it once or multiple times?

Replies: (list all replies)
Failure Charges
Patrick Hetherington Fri Sep 6 6:38:20 US/Eastern 2002
Failures
Wayne Fri Sep 6 12:09:12 US/Eastern 2002

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