Here is another good paper on the effect of gold in the solder joint. It
is a good description of gold nucleation over time.

http://physics.binghamton.edu/pub/cottsectc.pdf 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Saturday, October 25, 2008 1:21 PM
To: [log in to unmask]
Subject: Re: [TN] Au embrittlement on Copper vs Nickel

From my years of looking at solder joints, I've seen aged AuSn IMC's
'degenerate' to that degree that the components have lifted. A fresh
AuSn IMC must not be regarded a catastrophy, in fact it's strong while
not very flexible. When you run current through the joint and add a high
temperature, processes that I can't explain will start. The plates and
dendrites Werner mention are the same, but the small amounts of non-IMCs
that exist between the large platelets (kind of 'glue' ) begin to move
and more or less disappear. The result becomes a disastrous and rotten
solder joint that can break at the slightest mechanical movement. Am
sorry for not having the ultimate scientific explanation, but there are
guys who can satisfy your curiosity. One such is Mr Bulwith, once a
Sandia lab rat, don't know where he is now. Below is one of his many,
many papers about soldering to Gold over Nickel over Copper over Donuts
over River Kwai. Hope this gives you an idea.
/Inge

http://www.shanelo.co.za/List%20of%20articles/GOLD%20Soldering.pdf


----- Original Message -----
From: "Gumpert, Ben" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, October 24, 2008 11:03 AM
Subject: Re: [TN] Au embrittlement on Copper vs Nickel


> Dave,
>
> I'll see if I can track down a copy of the AWS Soldering Handbook, but
> the IPC-STD-001 HDBK doesn't go into the detail that I'm looking for.
>
> Are you differentiating between the brittleness caused by AuSn4 in the
> bulk solder and the brittle intermetallic layer that tends to form
with
> aging of the joint? I can understand the bulk solder brittleness being
> the same, but are you saying that the effect of Au on the strength of
> the intermetallic layer is not significantly different?
>
> Ben
>
>
> ________________________________
>
> From: [log in to unmask]
[mailto:[log in to unmask]]
>
> Sent: Friday, October 24, 2008 11:29 AM
> To: TechNet E-Mail Forum; Gumpert, Ben
> Cc: [log in to unmask]
> Subject: Re: [TN] Au embrittlement on Copper vs Nickel
>
>
>
> Hi Ben - gold embrittlement is a function of the amount of gold in the
> solder joint and not dependent on the pwb pad being copper or nickel.
> The IPC-STD-001 Handbook has a very good and short tutorial on gold
> embrittlement in section 5.4.1.1 on page 63/64 which would be useful.
> Also, there is good coverage of the topic in the AWS Soldering
Handbook,
> section 2.2 Contamination, pages 182-183. FYI - the AWS Soldering
> Handbook, ISBN 0-87171-618-6, edited by Dr. Paul Vianco, Sandia
National
> Labs, is one of those references that everyone must have on their
desks
> (IMHO). It covers a huge range of solder and soldering process topics
in
> a well written format.
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
> "Gumpert, Ben" <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
>
> 10/24/2008 09:58 AM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> "Gumpert, Ben" <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
> Subject
> [TN] Au embrittlement on Copper vs Nickel
>
>
>
>
>
>
> Technetters,
>
> Anyone care to share some comments on Au embrittlement?
> Specifically, what is the relative difference between joints on copper
> vs nickel? (For a SnPb joint)
>
> Does Cu inhibit AuSn4 from forming in the bulk solder? Does this have
> any effect on Au in the intermetallic layer?
> Do the intermetallic compounds containing Au of each joint result in a
> similar brittleness?
> Do the joints have the same propensity for growth of intermetallic
> compounds containing Au?
>
> Any thoughts are welcome.
> Ben
>
>
>
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