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: Mark Schofield
Date posted: Thu Feb 21 11:34:50 US/Eastern 2002
Subject: STANAG Interface for RMM
Does anyone have an experience on the in-service reliability of the STANAG 4575 interface for Removeable Memory Modules in terms of how often the RMM can be inserted/removed before replacement of the connector is necessary? We shall be using the MIL_DTL-24308E D-type connectors with our implementation. The standard requires a minimum durability of 500 make/break cycles for this connector. In the absence of supporting data this effectively lifes the interface at 500 times the average removal interval which is an unattractive proposition in terms of total ownership costs. Comparision wuith commercialy available non-STANAG interfaces for similar applications reveals claimed life-times of up to 25000 cycles. The truth probably lies somewhere in the middle - but where?
Subject: Connector Cycling
Reply Posted by: B.W.Dudley
Organization: Reliability Analysis Center
Date Posted: Tue Feb 26 9:26:01 US/Eastern 2002
The question on numbers of mating and de-mating of connectors is one that has been investigated and tested by a number of manufacturers. If the condition of operator or maintenance induced failure is not considered (bent pins), then the cycling factor is a condition of wear on the pins and receptacle. The common failure mode is increased contact resistance caused by pitting and corrosion due to wear. In searching the files for information, I found test data for plug-in connectors with 100 micro inches nickel and 100 micro inch gold plating. These connectors were rigorously tested for 3000 cycles and the contact resistance was measured every five hundred cycles. The change in resistance was negligible. The connectors were then aged for four months and re-tested and found to have little or no change in contact resistance. The final test was a one hour exposure to hydrochloric and nitric acid vapor which includes chlorine gas. This test is an excellent short term corrosion test for conductors. The results were no change in contact resistance. This testing was performed on 24 pin connectors.
I could not locate the specification MIL-DTL-24308, to see what materials are required for the contacts. If the contacts are nickel and gold plated, you should expect more than 3,000 cycles without any change in contact resistance. The five hundred make or break cycles stated in the specification is only a minimum value and higher levels should be expected. With regard to the commercial claim of 25000 cycles, I find this difficult to accept without rigorous testing followed by accelerated corrosion testing. Most of the durability statements that I found from the commercial vendors indicate 10,000 cycles, and are not supported with test factors.
So, my recommendation is to use the 3,000 cycles as a base line for nickel and gold plated contacts. This cycle rate is equivalent to one cycle per day for eight years before any change in resistance is expected.