SRC Forum - Message Replies
Forum: Reliability & Maintainability Questions and Answers
Topic: Reliability & Maintainability Questions and Answers
Topic Posted by: Reliability & Maintainability Forum
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998
Posted by: Brandon
Date posted: Thu May 8 4:05:41 US/Eastern 2003
Subject: Realistic Quality Factor for Reliability Prediction of Commercial Components
I am currently carrying out a reliability prediction for a military equipment that uses commercial components. I'm using Parts Stress Analysis. According to MIL-HDBK 217F, the "Pie Q" for these commercial components is above "1". This may be true more than 10 years ago, when 217F is being written, but is it still true now? Please advise. What is a more realistic "Pie Q" that I should use now? Can it be as low as "1"?
Thank you for your help.
Reply Posted by: B.W.Dudley
Date Posted: Mon May 12 10:08:19 US/Eastern 2003
The modification factors that are included in the reliability prediction procedure, MIL-HDBK-217, were developed using regression analysis techniques on historical data. MIL-HDBK-217 is an old document and the data that was used to develop the models is based on technologies that have been surpassed. The failure rates produced are very pessimistic, if one can perform the calculation. Some of the more complex devices are not included in the 217 parameters. The quality factor is one of the concerns that modern technology has by-passed. Today's devices are far more reliable than the technology of 10 years ago, which is when the last update to MIL-HDBK-217 was performed. Your question regarding the quality factor to be used is one that you must justify to your customer. I believe that the factors shown are out of scale for plastic encapsulated microcircuits, which have been shown to be as reliable as the hermetic devices. The RAC has a new concept called PRISM that has better capabilities and more flexibility in predicting reliability for complex microcircuit devices.