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: Benny
Date posted: Thu Dec 30 1:29:03 US/Eastern 1999
Subject: Derating guidelines for SMT
I am trying to find some derating guidelines with regards to Surface Mount Technology (SMT), especially in the area of microcircuits. Are such guidelines available? In general, are there any differences between the derating factors for SMTs compared to MIL-HDBK-338?
I understand that the latest derating study conducted by the former U.S Air Force Rome Lab in 1992 can be found in the technical report, RL-TR-92-11 (ADA253334). Does this study cover SMT? Please advise.Thanks.
Subject: SMT Derating
Reply Posted by: Bruce Dudley
Organization: Reliability Analysis Center
Date Posted: Tue Jan 4 14:22:55 US/Eastern 2000
Derating standards such as RL-TR-92-11 "Advanced Component Derating" and MIL-HDBK-338 "Electronic Reliability Design Handbook" do not have parameters for surface mount technology life extension. In-fact, solder connections are not included. The problem is the number of different combinations of material, environments, and stand-off height which results in a condition that requires individual calculations. Therefore, derating has to be engineering analysis of the materials, conditions and other factors.
Two books and one technical report could be used as guides in the analysis of the SMT problem. The books are: "Solder Joint Reliability Theory and Application" by John H. Lau, Van Nostrand Reinhold NY,NY, 1991 and "Design Guidelines for Surface Mount Technology by John E. Traister, Academic Press Inc., NY,NY, 1990. The report is: RL-TR-93-6, "Reliability Analysis of Surface Mount Technology (SMT)" by the Harris Corp, 1993. These documents have the models and engineering equations to determine the drating level that is necessary to extend the life of the product.