Hello Terry:
        We have had one experience similar to yours which may help shed 
     some light on your header problem. We had a gold/nickel over copper 
     base metal connector that built up resistance over time on a program. 
     Scanning electron analysis showed only the presence of nickel and gold 
     so we ruled out the possibility of copper diffusing through the nickel 
     (which should be very unlikely anyway!). After careful examination of 
     the SEM photo's we notice several "protrusions" in some of the porous 
     areas in the gold plating. Using Auger analysis we found that the gold 
     was porous enough that the nickel had diffused it's way to the 
     surface. We worked with the connector vendor on the quality of the 
     gold plating and the problem was resolved. I rarely see any 
     information on nickel diffusing to the surface of gold plating and I 
     wouldn't expect it to but then nothing is absolute. Good luck.
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: DES> Connector Reliability
Author:  [log in to unmask] at ccmgw1
Date:    4/29/96 12:37 PM


     
We have a header in a prototype system with brass sprung contacts with gold 
plate over nickel, contacting pins which are also gold-plate over nickel.
     
This connector carries 3A, and is showing a strong tendency to increase in 
contact resistance in field tests (up to 150 mOhm). Removing and refitting 
the connector takes the contact resistance back to "as new" (<40 m Ohm).. The 
connectors have been examined by a test lab and pronounced OK, with no 
contamination. No deposit or oxidation is visible on the surface.
     
Has anyone seen similar failure mechanism? What's the physics?
     
     
Terry Davey --------------------------------  [log in to unmask]  ------