Forum: Reliability & Maintainability Questions and Answers
Posted by:Richard Golek (Richard_Golek@Pittway.com )
Date posted: Tue Mar 7 15:01:03 US/Eastern 2000
Subject: Sulphur Dioxide corrosion testing acceleration factors
We are interested in any experience anyone has had in predicting the equivalent field life of small electronics assemblies as a function of long term exposure(weeks to months)in a controlled atmosphere of 25PPM sulphur dioxide. Relative humidity will be near 93%, and the temperature between 40C to 60C. The assemblies will be a mix of discretes and ICs, with some relays and switches. Ongoing functional testing will be conducted until failure modes emerge. The study will be an attempt to compare wax coated to unprotected product. Thank you.
Posted by: Leroy Meyers
Date posted: Mon Mar 6 15:16:54 US/Eastern 2000
Subject: Prediction "Degradation"
I work at a fairly small company. For our main product, a $200,000 unit for military communications, we have always advertised a certain MTBF which was obtained using MIL-HDBK-217F. Now, we are switching to all surface mount components, which hurts the prediction significantly because of the switch from B level or 883 parts to commercial non-hermetic parts. I could make assumptions, and give the commercial parts a better quality factor than 217 indicates. Or, I can switch to a different prediction technique such as Bellcore or Prism, or which I have no experience. Any opinions or other suggestions?
Posted by: David Cash (email@example.com )
Date posted: Fri Mar 3 10:14:03 US/Eastern 2000
Subject: error in MIL-HDBK-217F N2 ???
On page 10-2, CDR style chip capacitor has failure rate of .0020, but a CRW style chip has a rate of .00005. All other styles except variables have rates with at least 3 decimal places before first significant number. Is this a misprint in the manual???
Posted by: Bill Jones
Date posted: Mon Feb 28 19:27:08 US/Eastern 2000
Subject: Acceleration Factor (AF)
Where can I get the equations of AF under different accelerated stress conditions and/or different dominant failure mechanisms? For example, for thermal fatigue, AF=(delta Ta / delta Tu)^m; for vibration fatigue, AF=(Ga/Gu)^m. Are these correct? And how to determine the index m. I find there are huge differences in m among different resources. Could I find some references which provide better equations and their parameters? Thanks a lot.
Posted by: Shirish Puranik
Date posted: Fri Feb 25 14:53:52 US/Eastern 2000
Subject: ESS for electronics components
I have following questions.
1. During the burn-in tests of electronic modules do the units have to be powered up? Is there some literature that explains the principles of burn -in for electronics? 2. Where can I find the temperature and cycling guidelines including acceptable ramp rates for temperature during burn-in process?