No, I really wasn’t thinking about the Black Pad failures, I was just 
thinking about the gold embrittlement issue.

When Au and Sn are melted and combined, the Au goes into solution much like 
sugar and water.


There is some threshold level of Au concentration after which the Au and 
the Sn start to form their intermetallic compounds. Then there is probably 
another threshold level where the IMC start to accumulate in a 
concentration high enough to cause the embrittlement.

Of course if you add heat to the equation and temperature cycling you 
increase the likely hood of failure from both the IMC and mechanical stresses.

The few failed solder joints that I have had the opportunity to investigate 
were mostly at the IMs lines. A few at the IMs of the lead frame itself but 
mostly at the interface of the land and lead. Some of these failures have 
occurred after only 100 cycles from –40 to 175C. I have not seen any 
evidence yet were there was a gold intermetallic causing the failure, not 
to say no one else has.

With that said, I have seen in the past where the Au and Sn intermetallic 
compounds have caused solder joint failure but that was when resistors and 
DIPs were plated with gold.

So I am looking for evidence that the ENIG process is causing this problem.

Donald

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


At 09:15 AM 4/16/2005, you wrote:
>Don,
>
>I interpret your question correctly, it sounds like you are asking if
>you can have "Gold Embrittlement".  I believe you are asking the
>question because you have heard a lot of differing views concerning ENIG
>Black Pad brittle failures.  One thing you shouldn't do is assume that a
>Black Pad failure is "Gold Embrittlement".  There is a difference.  As
>indicated in our ISTFA 2000 paper "Case Studies of Brittle Interfacial
>Failures in
>Area Array Solder Interconnects" one of the conclusions was "Two
>distinct Ni/Au embrittlement failure modes are verified. Embrittlement
>caused by formation of a secondary, Au-Sn intermetallic is fairly well
>understood. Embrittlement caused by poor electroless or immersion
>plating processes is not understood."
>
>I'll provide two answers to your question:
>
>Q1. Can you have "Gold Embrittlement" with ENIG
>
>A1. Yes if the ENIG solder joint has undergone long isothermal aging and
>the gold-tin IMC accumulates at an interface.
>
>Q2. Is a "Black Pad" brittle fracture due to "Gold Embrittlement"
>
>A2. No.  The "Gold Embrittlement" caused by formation of a secondary
>gold-tin intermetallic has been evaluated for years and is fairly well
>understood.  The "Black pad" brittle fractures are different and appear
>to be associated with the ENIG electroless and immersion plating
>processes and in my mind they are not well understood.
>
>My experience suggests that "Gold Embrittlement" happens when solder
>joints are made to electrolytic plated NiAu surface that have thick gold
>and "Black Pad" happens sometimes when solder joints are made to ENIG
>plated surfaces.  The only similarity between these failures is that
>they brittle fractures at an interface.
>
>Regards,
>George
>George M. Wenger, Andrew Corporation
>Reliability / FMA Engineer
>Base Station & Subsystems Group
>40 Technology Drive, Warren, NJ 07059
>(908) 546-4531 [log in to unmask]
>
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Donald Kyle
>Sent: Saturday, April 16, 2005 9:32 AM
>To: [log in to unmask]
>Subject: [TN] ENIG Gold Embrittlement
>
>I have heard a lot of differing views about Gold Embrittlement lately
>here
>and I am curious, has anyone here found evidence that ENIG causes this?
>
>  From what I have read, the ENIG process lays down about 120 to 240
>micro
>inches of Ni and 2 to 4 micro inches of Au.
>
>If you calculate the percent by weight of Au in the solder joint, you
>have
>to have a very very thin stencil to even come close to having a problem
>with the Au.
>
>I have seen the following data from several different sources and most
>recently in a workshop presented by George Milad and Donald Gudeczauskas
>of
>Uyemura International Crop at APEX this past February. Their data shows
>that with a 5-mil stencil and a Au thickness of 20 micro inches, the
>percent of Au in the solder joint is 1.54%. Now of course, you are not
>going to get 20 micro inches out of this immersion process and even if
>you
>plated the Au, this is just at or below the threshold for Au
>embitterment.
>
>So with a nominal thickness of say 5-micro inches of Au and a 5-mil
>stencil, the percent by weight of Au in the solder joint would be 0.38%.
>
>Would this be a problem? I don't think so. So has anyone evidence that
>it does?
>
>Below are just two of many sites talking about gold embrittlement. These
>
>have some neat pictures to go along with the text.
>
><http://www.npl.co.uk/ei/documents/gold.pdf>http://www.npl.co.uk/ei/docu
>ments/gold.pdf
>
>http://www.alphametals.com/products/solder_solutions/pdf/soldergld.pdf
>
>
>
>
>Donald Kyle C.I.D.+
>281-285-7528 voice
>281-285-8593 fax
>[log in to unmask]
>Schlumberger
>Sugar Land Product Center (SPC)
>Mail Drop MD155-1
>155 Industrial Boulevard
>Sugar Land, Texas 77478
>
>
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