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August 2008

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From:
"Douglas O. Pauls" <[log in to unmask]>
Date:
Tue, 26 Aug 2008 13:22:42 -0500
In-Reply-To:
<03BCFDB9152C47EDB040561F31D73178@ingemar2a39615>
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TechNet E-Mail Forum <[log in to unmask]>, Inge <[log in to unmask]>
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TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
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Well, I guess that depends on what the previous meal was.  I don't know if 
methane has the same harmful effect on immersion silver as sulfur.  I 
suppose I could go knock back a dozen or so deviled eggs and let you 
know......

And Dewey, that was a horrid pun, even for you.  Well done.

Doug Pauls




Inge <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
08/26/2008 10:12 PM
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TechNet E-Mail Forum <[log in to unmask]>; Please respond to
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Subject
[TN]






So a TV living with a gaseous family is at risk?
Inge


----- Original Message ----- 
From: "Woolley, Mark D. (Mark)" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, August 26, 2008 7:37 AM
Subject: [TN]


Any environment that contains sulfur, like hydrogen sulfide or sulfur
dioxide should preclude the use of IAg.  The sulfur will react with the
silver and "grow" sulfides which can be electrically conductive
resulting is shorts between vias.  This can occur even when the
concentrations are within OSHA limits for human exposure.
Silver sulfides can be semiconductors or conductors depending on the
chemical composition.  They are black in color instead of silver, any
exposed silver will be affected.

Mark Woolley
Failure Analyst

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of James Verrette
Sent: Tuesday, August 26, 2008 8:25 AM
To: [log in to unmask]
Subject: [TN]

What characteristics of the end use environment would cause IAg to not
be an appropriate finish and why?

Jim Verrette
Senior Electrical Engineer

------------------------------

Date: Mon, 25 Aug 2008 08:24:35 -0500

From: "Stadem, Richard D." <[log in to unmask]>

Subject: Re: ENIG White paper

Dave,

You write as if you are not at all familiar with IAg, which is totally

understandable. However, IAg has been around in full production mode for

many years now, and is rapidly becoming the most-used finish in the

market. Do not confuse it with immersion tin finish, which has little or

no shelf life.

IAg-finished circuit boards have a recommended shelf or storage life of

about 1 year. However, if packaged properly in a hermetically sealed bag

with silver saver paper liners, and stored away from sulfates, it is

possible to use boards up to 5 years old or even longer with no issues

whatsoever. All you need to do is call out the packaging on the

fabrication drawing per IPC 4553.

I have soldered IAg boards that sat around exposed to the elements for

more than 4 years in previous lives, and they soldered up just fine, no

change in the DPMO.

Some of the bare boards we use here at GD are 34" by 40", 48 layers,

1/2" thick, cost is about $48,000 each. Their finish is IAg. =20

I have had a lot of experience with IAg over the past 10 years or so,

having seen at least 150,000 IAg boards assembled and soldered with

every type of component you can think of, and I have never experienced

any issues with them. I have experienced many, many issues with ENIG,

however, and that is the finish that would keep me up at night waiting

for the bomb to go off. There are many reliability issues associated

with ENIG such as black pad, brittle nickel, etc., etc, but just think

about the fact that you are soldering to nickel, which has a dissolution

rate about 50 times slower than copper.

Should you ever have a solderability issue with IAg, you can have the

fabricator rework the finish. If you have an issue with ENIG, the only

thing you can do is rework your scrap account.

However, you need to take the end-use environment into consideration

when you select a circuit board finish. ENIG (unfortunately) may be your

best choice. I would fully qualify just one assembly at a time, and I

would fully qualify it. For Space use, I would not suggest IAg.

-----Original Message-----


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