Hi TechNet! Just an update on the galvanic compatibility discussions we had
earlier in the year. I have finished the environmental testing with
wonderful success! Both immersion silver and immersion gold pwb surface
finishes survived 270 hours of 85C/85RH Humidity and 48 hours of ASTM B117
salt fog testing with no galvanic reactions with aluminum contact surfaces.
The pwbs were biased during the testing and the aluminum surfaces were
bare, no conversion coat condition. I am in the process of writing up the
test results which will be published at the IPC Fall meeting this September
in Minneapolis. Thanks to everyone for their ideas/suggestions/hypothesizes
on the issue.

Dave Hillman
Rockwell Collins
[log in to unmask]




-----Original Message-----
From: Dave Hillman [mailto:[log in to unmask]]
Sent: Tuesday, February 04, 2003 3:12 PM
To: [log in to unmask]
Subject: [TN] Galvanic Corrosion Testing

Hi TechNet! I am on a quest for some information and hoping the minds of
TechNet can send me charging off in the right direction. Rockwell Collins
has been very active in implementing the new immersion pwb finishes
(immersion tin, immersion silver, ENIG). The implementation has been very
successful with few "bumps in the road" being encountered. However, one
question has arisen that; a) as a metallurgical engineer I should have
anticipated and b) you would think someone else would have solved already.
The question is " Is there a galvanic corrosion issue with the use of
either ENIG or immersion silver pwb surface finishes and the aluminum
chassises/enclosures"? As background,  there is very little of the pwb
finish in intimate contact with the aluminum chassis with most of the
contact being aluminum standoff posts contacting a circular mounting pad on
the pwb. I have spent a number of hours looking for some type of galvanic
corrosion test which I could run to determine if either immersion silver or
ENIG finishes would be an issue. The two environments I have the most
interest in are temperature/humidity and salt air. I am tentatively going
to run an 85C/85%RH and an ASTM salt fog exposure on some mockup test sets
to see if I have any reactions. Has anyone run such a test or can anyone
direct me to a Mil STD or ASTM standard which deals with galvanic corrosion
of contacting dissimilar metals?

Thanks in advance.

Dave Hillman
Rockwell Collins
[log in to unmask]

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