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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: Eduard Porst (porst@teldix.de )
Organization:TELDIX GmbH
Date posted: Fri Apr 14 10:41:27 US/Eastern 2000
Subject: Quality factor for microcircuits
Message:
What is the equivalent MIL-HDBK-217F quality level (PiQ =0.25 or PiQ=1) for a microcircuit purchased to a Standard Military Drawing, device class V (for space applications) ?


Reply:

Subject: PiQ factor for class V microcircuit
Reply Posted by: Jack Farrell (jfarrell@alionscience.com )
Organization: Reliability Analysis Center
Date Posted: Tue Apr 18 10:28:32 US/Eastern 2000
Message:
Per MIL-HDBK-217FN2 a microcircuit procured in full accordance with MIL-PRF-38535 and Appendix B thereto (Class V) may be assigned a PiQ factor of 0.25. Therefore, if your subject microcircuit is procured per the above, from a vendor QML listed for Class V devices, then you may use a factor of 0.25 for PiQ in your 217 predictions. Please note that the models in MIL-HDBK-217 were developed utilizing data that is at least ten years old and may not accurately model current microcircuit processes. I would like to reiterate Mr. Dudley’s previous response on this forum that “The information that we are seeing indicates that screening of microcircuits is adding very little to the overall quality of industrial high reliability grade devices. In the last ten years, the quality levels of microcircuits has risen without the need for any extra testing, in fact some extra testing actually decreases the reliability by adding unneeded stresses. In our new PRISM model for microcircuits, we are using a process grading function that evaluates the device manufacturer's process along with the assembler processes. Extra testing does not factor very high in this assessment. Consideration of use of ISO-9000 procedures and Statistical Process Control methodology have been found to be more important in developing overall part quality.” Also, for your information SMD is an abbreviation for Standard Microcircuit Drawing.


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