Hi Dave,
We agree, with imAg you do not have enough Ag to cause Ag-embrittlement.
The original e-mail query did not talk about imAg but generalized 'silver finishes'. That may be including imAg, but also thicker [it included (thin?) which to me meant it could be thicker and therefore not imAG] electrolytic and other Ag deposits.
So indeed, the devil is in the details——IT DEPENDS!
I also agree with your 'general rule', it comes about because very little Ag-plating other than imAg is in fact done.
Werner
-----Original Message-----
From: [log in to unmask]
To: TechNet E-Mail Forum <[log in to unmask]>; Werner engelmaier <[log in to unmask]>
Cc: [log in to unmask]
Sent: Tue, 27 Jan 2009 11:45 am
Subject: Re: [TN] SnPbAg solder and Immersion Silver PCBs
Hi Werner! I don't believe that there
is an silver embrittlement issue with the use of ImAg PCBs. Rockwell Collins
has been using ImAg PCBs for over 10 years with no issues of silver embrittlement.
We have also conducted several lead-free assembly studies using the SAC305
solder alloy and have found no issue with silver embrittlement. And, the
IPC 4-14 Plating committee did not find any silver embrittlement issues
with a test assembly that was excessively silver loaded - ImAg PCB finish
and silver in the solder paste - and we did not find any evidence of silver
embrittlement. The 4-14 committee will be publishing that study as an IPC
Technical Report in the near future after completing the necessary committee
revi
ews. As a general rule of thumb, I think silver embrittlement is on
a much lower risk register than gold embrittlement. However, I have seen
the PLCC study data and it indeed was a case of silver embrittlement so
I think that each situation needs to be understood to avoid having an embrittlement
issue.
Dave Hillman
Rockwell Collins
[log in to unmask]
Werner engelmaier <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
01/27/2009 10:30 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Werner engelmaier <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] SnPbAg solder and
Immersion Silver PCBs
Hi Kevin,
That "thin (?) silver finishes...prevent the dissolution of the component
lead into the solder joint" is a Red Herring.
All you may be getting is AG-embrittlement which is just as bad as Au-embrittlement.
It was just such 'silver finishes' on TI PLCCs that caused those PLCCs
to fall off PCBs during bed-of-nail testing in 1982 at IBM-Austin and resulted
in the formationof the IEEE Compliant Lead Task Force.
Also, how would an Ag-finish prevent the formation of IMCs with the lead
metal?
Werner
-----Original Message-----
From: Kevin Glidden <[log in to unmask]>
To: [log in to unmask]
Sent:=2
0Tue, 27 Jan 2009 8:35 am
Subject: [TN] SnPbAg solder and Immersion Silver PCBs
Morning all,
Question today about SnPbAg solder. We have always used Sn63Pb37
solder
alloy for all products, with exception of some high temp solders for special
cases. The lion's share of our PCBs are ImAg finish, 5 to 12 micro-inches,
per IPC-4553. In reading about SnPbAg solder, it appears to be recommended
for use on SMT components with thin (?) silver finishes. This is
to prevent
the dissolution of the component lead into the solder joint. Drawbacks
appear to be only that the joint is not as shiny and reduced mobility of
the
solder. Is it also considered good practive to use an SnPbAg alloy
for
immersion silver PCBs for the same reasons? Any tech articles available
on
this?
Thanks (again!)
Kevin Glidden
Manufacturing Engineer
Luminescent Systems Inc.
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