Hey Richard,
Thanks for the reply.  I was hoping to stir a little.  But, let's make sure we're on the same page first.
Do you mean that you have ImAg exposed to the environment after assembly?
Chris

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Thursday, April 16, 2009 3:45 PM
To: [log in to unmask]
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?

Ditto. Ditto. Ditto.

Chris,
About your statement: "As far as I know, the jury is still out on ImAg, ImSn as final via finish.  Considering creep, tarnish, whiskers, porosity... I wouldn't go there".

Please provide documentation on these issues. I have not seen that here in the U.S.

We have built a lot of high-reliability Class 3 CCAs with IAg used as a final finish here at GD. We are currently building more than one contract that requires a 20-year life with 99.95% reliability utilizing a very large 48 layer PWB. It costs over $100,000 for 1 (one) PWB.
The surface finish is .....drum roll, sounds of cans of Mountain Dew being snapped open.....Immersion Silver.

Outside of GD, I have seen thousands upon thousands of IAg boards used for medical, telecommunications, and industrial applications, with very few (I can count them on one hand) via issues related to the finish. Of those, none were associated with a proven finish product such as Sterling and were nearly always the result of other fabrication issues unrelated to the finish.

I have yet to see an IAg finished board with a via failure attributed to porosity, tin whiskers, creep, etc., except where there were design issues unrelated to the surface finish.

On the other hand, I have seen ENIG PWBs with via cracks, albeit rarely.

But I have seen many more issues with ENIG SJs that dwarf via reliability issues in comparison.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Thursday, April 16, 2009 2:32 PM
To: [log in to unmask]
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?

Hi Joyce - my response would "it depends" (and Doug gets another Diet Mt.
Dew) as Rockwell Collins utilizes immersion silver pwb surface finishes on many IPC Class 3 type products with no reliability issues.

Dave



Joyce Koo <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
04/15/2009 04:11 PM
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Subject
Re: [TN] Gold/Tin Intermetallics, why are we afraid?






"ImAG finishes have a 12-month shelf life in a controlled environment (<35[degrees]C/<85[degrees] RH), which can be significantly shortened when exposed to air pollution with high sulfur and chlorine content.
Silver embrittlement Embrittlement

A general set of phenomena whereby materials suffer a marked decrease in their ability to deform (loss of ductility) or in their ability to absorb energy during fracture (loss of toughness), with little change in other mechanical properties, such  ([Ag.sub.3]Sn intermetallics) of solder joints may occur when the finish thickness exceeds IPC-4553 recommendations and Pb-free, high silver content solders are used. ImAG is not recommended for high-reliability assemblies that must meet IPC-6010 Class 3 requirements, but is acceptable for Classes 1 and 2."

http://www.thefreelibrary.com/Will+discoloration+tarnish+ImAg+reliabilit
y%3F+Watch+for+silver...-a0193896272

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: Wednesday, April 15, 2009 4:34 PM
To: [log in to unmask]
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?


 Hi Vlad,
I cannot comment on your specific case, but look at the pics below to see Ag-embrittlement.
Sorry 'Netters, IPC strips pics.

Werner

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