The environment could be supplying the sulfur causing the tarnish and
miscellaneous packaging products.

Victor,

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, December 04, 2007 9:33 AM
To: [log in to unmask]
Subject: Re: [TN] SILVER IMMERSION BOARDS ISSUE

Jon,
Immersion silver boards, if packaged and stored properly to begin with
per IPC-4552, typically have little problems with tarnishing in the
initial reflow oven. However, if they have been allowed to sit around
exposed to air, and then you bake them prior to assembly and reflow, you
may get some tarnishing simply from the heat of the bake oven and the
reflow. However, I have yet to see any IAg boards that did not solder
right up in spite of a small amount of tarnishing (yellow appearance).
The tarnishing is not so much from any sulphur (although that would
certainly contribute) but more so the heat. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roberts, Jon
Sent: Tuesday, December 04, 2007 8:31 AM
To: [log in to unmask]
Subject: Re: [TN] SILVER IMMERSION BOARDS ISSUE

Guy, my message was not clear enough. I was referring to any over used
to bake the boards prior to processing. The reflow oven is where the
tarnish started to show up so we are thinking the sulfur was getting
deposited prior to reflow. The assemblies may get through first pass but
shows up after second pass before wave solder machine. Also the BGA's
pads is most susceptible to the tarnishing of the silver coating. Thanks
for your input, Jon

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas O. Pauls
Sent: Tuesday, December 04, 2007 8:06 AM
To: [log in to unmask]
Subject: Re: [TN] SILVER IMMERSION BOARDS ISSUE

Guy,
I have been involved with the SIR Handbook for quite some time and can't

recall any sections on cleaning SMT reflow ovens.  Humidity chambers,
yes. 
 Reflow ovens, no.

Doug Pauls




Guy Ramsey <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
12/04/2007 07:57 AM
Please respond to
[log in to unmask]


To
[log in to unmask]
cc

Subject
Re: [TN] SILVER IMMERSION BOARDS ISSUE






Yes, I think our problem was oven contamination. We started wrapping
immersion silver boards in aluminum foil (loosely) during the bake. We 
have
not had any problems with delaminating or solder performance using this 
bake
out process. 

We have not tried to clean the oven yet, as we rarely see immersion 
silver.
I understand it is rather difficult. I think there are instructions in
the
IPC SIR Handbook. 

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