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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:Richard Golek (Richard_Golek@Pittway.com )
Organization:System Sensor
Date posted: Tue Mar 7 15:01:03 US/Eastern 2000
Subject: Sulphur Dioxide corrosion testing acceleration factors
Message:
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.


Reply:

Subject: Sulphur Dioxide Accelerated Corrosion
Reply Posted by: Bruce Dudley (bdudley@iirtr.org )
Organization: Reliability Analysis Center
Date Posted: Thu Mar 9 10:02:17 US/Eastern 2000
Message:
All accelerated testing is difficult as one must first determine the accelerating parameters. This is usually does through experimental testing. Your problem is complicated by the moisture time delay function of the wax coating. Since this wax coating is not a hermetic seal, moisture and sulfite ions will permeate the coating. Your problem is the thickness and uniformity of the coating. Variables such as defects, material content and application processes will cause many variations in the test results. Acceleration factors will be difficult to develop with the number of expected variables in the wax coating. The electronic assemblies can be modeled using the Arrehenius steady state temperature acceleration model for estimating chemical aging effects or by using the Peck model for accelerated combined temperature-humidity effects. The activation energies for these models can be determined experimentally or by use of a super-positioning of the individual corroison parameters.


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