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| Date: | Wed, 30 Sep 2009 11:21:45 -0400 |
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People panic about silver migration, which is not really an issue.
However, there apparently is a very serious problem that can occur on uncoated boards in high sulfur environments, where somehow the silver acts to catalytically cause the copper to redeposit in random directions. Doesn't even need a voltage to cause this phenomenon!
A paper on this was brought up to this forum several months back. If you search the archives on ImAg you should be able to find it. The growths are nice black dendrites.
Wayne Thayer
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Harner, Chester
Sent: Wednesday, September 30, 2009 11:03 AM
To: [log in to unmask]
Subject: [TN] Immersion Silver for Class 3 Boards
The revised Immersion Silver IPC spec (4553A) indicates that Immersion
Silver is not recommended for Class 3 boards. There is no stated reason.
I have been looking into Immersion Silver for all the same reasons as
everyone else, to replace HASL for flatness etc. It looked very good
until the Class 3 problem.
Does anyone know why IAg would not be recommended for Class 3 boards?
Chet Harner Sr. Engineer Crane Hydro-AirePO Box 7722 Burbank Ca -
91510 818-526-2600 x3557
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