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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum (src_forum@alionscience.com )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Original Message:

Posted by: James
Date posted: Mon Jun 26 17:50:57 US/Eastern 2000
Subject: Pi Factors in 217
Message:
In 217, I noticed that there are two factors (power rating factor and voltage stress factor) in the equation of Bipolar (transistors, low freq.) , but not in Si FET (transistor, low freq.). Why? I think there are still some power and voltage effects on the failure rate of FET. Could I use the tables in Biploar to modify the equation of FET? Thanks in advance! James


Reply:

Subject: MIL-HDBK-217 Low Frequecy Transistor Model
Reply Posted by: Jack Farrell (jfarrell@alionscience.com )
Organization: Reliability Analysis Center
Date Posted: Fri Jun 30 10:46:06 US/Eastern 2000
Message:
The failure rate models for Low Frequency Transistors were based on a study performed in 1988 and documented in RADC-TR-88-97 “Reliability Prediction Models for Discrete Semiconductors Devices”. In developing the Si FET model insufficient data was available to determine an electrical stress factor and this factor was left out of the model. Data available for determining a power rating factor was limited and the effect on failure rate due to power rating was folded into the application factor. To answer your question, the effects of power rating are already addressed in the application factor and the effects of electrical stress could not be determined. To arbitrarily adjust the Si FET model with the Bipolar models voltage stress factor would invalidate the results.


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