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: SPM
Date posted: Fri Feb 9 9:25:03 US/Eastern 2001
Further to my question of the 15 January, I have read through several documents regarding ESS. The general consensus is that there should be a minimum of 10 cycles for an effective ESS program. Could somebody tell me how this figure was arrived at and why not less than 10 and is there a calculation that can be done to determine an effective number of cycles for a new product.
Thanks in advance
Reply Posted by: Bruce Dudley
Organization: Reliability Analysis Center
Date Posted: Mon Feb 19 10:32:34 US/Eastern 2001
The specific number of ESS test cycles is an estimate based on previous test experience. Testing should start at high number of cycles to make sure that all defects are removed, then lower the testing to the most economical level. The rate of fall-out of defects is dependent upon may features including the quality of the manufacturer and the components. In the Reliability Toolkit; Commercial Practices Edition, the number of test cycles varies as to the level of test performed. That is, more cycles for circuit boards (20 to 40) and less for complete units (12 to 20). Determining the exact number of cycles should be done by actual testing. If the failures occur well before ten or twelve or twenty cycles, then reduced testing could be considered. MIL-HDBK-344, Military Handbook, Environmental Stress Screening of Electronic Equipment has equations to measure the test results and the amoumt of useful life expended in the test.