Dave, coming from a metallurgical background myself, I also had the same
concerns as yourself with regard to ENIG finishes and Al cases. We use a
chromic conversion (alocrom 1200) finish on our box interiors and despite
extensive salty dog/humidity tests on both sealed and open assemblies have
failed to generate corrosion on the Al (cast A356). I would be interested to
discuss the testing etc with you off-line as despite satisfactory test
results, it don't feel right with a p.d. that big.

Regards
        Ian Fox
        Principal Process Engineer

        GOODRICH Engine Control Systems
        York Road
        Hall Green
        Birmingham
        B28 8 LN

        Tel: +44 121 607 3763
        e-mail: [log in to unmask]


-----Original Message-----
From: Dave Hillman [mailto:[log in to unmask]]
Sent: 04 February 2003 20:12
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]

---------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To
unsubscribe, send a message to [log in to unmask] with following text in the
BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet
NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send
e-mail to [log in to unmask]: SET Technet Digest Search the archives of
previous posts at: http://listserv.ipc.org/archives Please visit IPC web
site http://www.ipc.org/html/forum.htm for additional information, or
contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------