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September 2009

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Subject:
From:
"Wenger, George M." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Wenger, George M.
Date:
Wed, 30 Sep 2009 10:31:22 -0500
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Wayne,

Your first sentence says it all.  People panic about silver migration, which is not really an issue.

I think the paper you are referring to was on creep corrosion.  There have been cases where creep corrosion has been seen on immersion silver boards and that brought about another reason for people to panic. However, the creep corrosion reports I've seen show that creep corrosion occurs when OA flux residue is left on a board and it doesn't matter if the surface finish is immersion silver, immersion tin, or OSP.  Creep corrosion is due to contamination and not to immersion silver.  

Regards,
George
George M. Wenger
Andrew Solutions
Senior Principal FMA/Reliability Engineer
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 (Office) (732) 309-8964 (cell)
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne - IIW
Sent: Wednesday, September 30, 2009 11:22 AM
To: [log in to unmask]
Subject: Re: [TN] Immersion Silver for Class 3 Boards

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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