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April 2005

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Subject:
From:
Vladimir Igoshev <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Vladimir Igoshev <[log in to unmask]>
Date:
Sat, 16 Apr 2005 15:39:07 -0400
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text/plain (281 lines)
Thank you George,
 
I completly agree with you. I probably should have been more specific talking  about the BP and brittle fracture. :-) what I meant is that if a component can be almost blown off the board, then I wouldn't call it a case of  fracture at all. 
I referred to Ni-p later just because many thinks that the layer is involved somehow, but again only for ENIG!!!  It puzzles me why it happens with electrolytic plating, but it's a different story all together.

Have a nice weekend (whatever of it you have left). :-)


Vladimir
Sent from my Blackberry Wireless 
Vladimir Igoshev, 519-888-7465 ext.5283


-----Original Message-----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Sat Apr 16 13:29:05 2005
Subject: Re: [TN] ENIG Gold Embrittlement

Vladimir,

No need to be sorry.  You can intervene anytime because I respect your
opinion and observations.  I'm certainly not well versed in fracture
mechanics and have never had enough time to do a through study of "Black
Pad" failure.  My view of brittle fractures is simplistic.  I view a
brittle fracture as a rapid run of a crack or cracks through a stressed
material that leaves a relatively flat surface that exhibits very little
if any sign of plastic deformation.  Given this view, you can tell why I
thing the "Black Pad" and "Gold Embrittlement" failure signature look
like brittle fractures.

Secondly, I don't think in my response to Don that I indicated that the
gold embrittlement fracture path goes along the intermetallic/Ni-P
interface.  We've seen "gold embrittlement" brittle fractures on solder
joints to both ENIG and electrolytic plated NiAu, who's Ni contains no
P, surface finishes.  The majority of brittle fractures we've seen
appear to be intergannular in that they occur along grain boundaries and
once in a while we'll see transgrannular fractures (i.e., fractures
through grains).  Actually, on many of the brittle fractures we've
analyzed we have seen fractures between the Au-Sn intermetallic and bulk
solder, between the Au-Sn intermetallic and adjacent Ni-Sn
intermetallic, between the Au-Sn intermetallic and plated Ni, as well as
through the Au-Sn intermetallic.

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: Vladimir Igoshev [mailto:[log in to unmask]] 
Sent: Saturday, April 16, 2005 10:41 AM
To: [log in to unmask]; Wenger, George M.
Subject: Re: [TN] ENIG Gold Embrittlement

George,

I'm sorry but I'd like to "intervin e". Firsty, I think the "Black Pad"
isn't exactly a case of brittle fracture (from the fracture mechanics
point of view), and  we know that "Brittle Fracture" is an another  type
of the problems ENIG is prone to.  

Secondly, in case of gold embrittement, the fracture path doesn't go
along the intermetallic/Ni-P layer interface (at least from what I've
seen and know).

Regards,

Vladimir.
Sent from my Blackberry Wireless 
Vladimir Igoshev, 519-888-7465 ext.5283


-----Original Message-----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Sat Apr 16 10:15:14 2005
Subject: Re: [TN] ENIG Gold Embrittlement

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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