Since I was one of those who brought up the DeoxIT / ProGold usage, I'd like to post the following report I received from another list member. I hope he doesn't mind, as he'll remain nameless, and I've removed a thing or two from the report which might identify his major aerospace company. I found the report rather illuminating.
To save you from Googling, I believe "cots CCA" to simply be "commercial off-the-shelf circuit card assembly," i.e not a custom designed card for the application. "VME/VXI buss" refers to (I think) a series of common-sized cards, or boards, used in a variety of equipment. "Investigation into the MCG lockup condition identified the cause to be a high contact resistance from fretting corrosion. The corrosion is a result of the flash (~4 micro inches) gold plating on the DIN connectors not being greater than 30 micro inches. Regardless on the cots DIN connectors, Fretting corrosion is corrosion that can occur on the load bearing contact surface between mating material when gold plating has been worn through. One of the contact failure modes of electrical contacts is fretting corrosion. The corrosion results in unacceptable increases of contact resistance in mated connectors. Fretting corrosion occurs in separable contacts, when the contacting surfaces are submitted to small amplitude movement (micro-motion) relative to each other. This can be caused by vibration, shock, or thermal expansion. One of the symptoms for fretting can be identified where reseating of CCA’s in the system results in clearing the failure mode. Examination of the connector mating surface under a scope will reveal a black residue (non-conductive oxide) on the contacts. <snip picture of gold pins with black residue> This corrosion results in a high resistance contact area thus causing a failure in the system. The reseating of the CCA’s results in a scrubbing action that removes a layer of the oxide where contact is made and the process starts again. One method used to inhibiting fretting corrosion is the use of lubricants. This was recommended by our components engineer <snip>. The lubricant reduces friction, wear, and to some extent shields the surface from the air. The oxide formation can be decreased by limiting available oxygen. The lubricant/cleaner we chose is from Miller-Stephensen, part number MS-383H with UV indicator. The UV indicator aids in the inspection process to insure coverage of the contacts. We also had our M&P lab review the lubricant and agreed this was a good choice. The lubricant was added after cleaning of the connectors with alcohol as recommended by the lubricant supplier, since these were connectors that already exhibited the corrosion. After cleaning the lubricant was added to the connector pin side and mated to the VXI/VME interconnect chassis. Conclusion is all ground programs utilizing DIN connectors, VME/VXI buss, or cots CCA’s in these chassis should use the connector lubricant to reduce the risk of intermittent failures from fretting corrosion. Connector design guidelines are found on the components engineering webpage. The lubricant is not recommended for airborne applications. Airborne applications need to specify the minimum gold thickness allowed per the components engineering webpage guidelines." 73, Mike KW1ND _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
