Hi George,
The 3% silver in SAC305 are uniformly distributed throughout the solder
joint; the Ag from surface treatments typically concentrates near the
interfaces.
Werner

-----Original Message-----
From: [log in to unmask]
To: [log in to unmask]
Sent: Fri, 11 Aug 2006 12:17 PM
Subject: Re: [TN] silver embrittlement

   Sue,

You have every right to be confused, as the chairman of the plating
committee that put out the specification 4553, I have gone back and
re-read the
specs. The specs refer to thin silver and thick silver.

My apologies for the poor choice of terminology, the intent was to
differentiate between the Alpha Level product which could only produce
a very
thin
coating and the rest of the Immersion silvers out there that could
produce  a
thicker coating. So "thin" is a spec for Alpha level only and the
"thick" is
the
spec for all other immersion silvers.

For users not specifying Alpha Level the spec is:
5 uins minimum, typical 8uins-12uins.
Thick silver would be silver at 20uins or higher.

Thicker silver is unnecessary and may give rise to compromised solder
joint
strength. I am not sure that embrittlement is the main defect here,
after  all
the Pb/free SAC 305 alloy contains  3% silver.


George Milad
(Chairman IPC  Plating  Committee)
National Accounts Manager for  Technology
Uyemura International Corp (UIC)
249 Town Line Rd
Southington CT 06489
[log in to unmask]
Cell: (516) 901  3874

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