Hi Per Erik - looks like I have some additional reading to do! I have read
some of the references you listed and in several instances the
investigation results are not in agreement with the results I have on
product products. George Milad/Don Gudeczauskas and I have discussed their
work on a couple of occasions - good investigative work but there are a
couple of inconsistencies in comparison with production product results.
The industry is now starting to utilize the ENEPIG surface finish in a
wide number of applications which is why the IPC 4-14 committee completed
a tremendous amount of work to get the IPC-4556 specification completed.
Both the CALCE and Unovis consortiums have completed or have in progress
investigations which include the ENEPIG surface finish so there will be
more published data coming to light later this year. Pd creates a
complication for soldering processes due to its slow dissolution rate. The
PdSn4 intermetallic phase causes the same problems as the AuSn4
intermetallic phase so care must be taken to have sufficient soldering
process time and temperatures to avoid causing solder joint integrity
issues. I think as the industry becomes more mature in its use of ENEPIG
as a surface finish we will see some of the concern over the intermetallic
phase created eliminated. I have put the ENEPIG surface finish through IPC
Class 3 testing and it has passed those requirements. It will be
interesting to see the test results published later this year.
Dave
From: Per-Erik Tegehall <[log in to unmask]>
To: TechNet E-Mail Forum <[log in to unmask]>,
"[log in to unmask]" <[log in to unmask]>
Date: 03/13/2013 04:18 AM
Subject: RE: [TN] IPC-7095C vs IPC-4556 ENEPIG for SnPb
It is not only IPC-7095C that warn against using ENEPIG in combination
with SnPb soldering. In all papers I have, which have compared the
reliability of solder joints to ENEPIG using SnPb and lead-free solders,
the authors have all concluded that SnPb soldering gives solder joints
that are much more prone to brittle fractures in the IMC layers than
solder joints with SAC305 and especially after high temperature aging
(list of references is given below). It seems as if it is the Cu in the
solder that makes the difference since Sn3.5Ag also gives solder joints
prone to brittle fractures whereas addition of Cu to SnPb eliminates the
brittleness.
In all papers listed below, the evaluations of the reliability has been
performed using high speed shear or pull testing, which is usually
recommended for evaluation of the inclination for formation of brittle
fractures. Thus, they do not tell the performance of the solder joints in
a temperature cycling test. In fact, I have not seen any comparison of how
the fatigue life of the solder joints of SnPb and SAC305, respectively, to
ENEPIG is affected in temperature cycling tests.
The main objections I have to the evaluation referred to in IPC-4556 are
that the shear testing was performed using a very low shear rate (500
µm/s) and that no testing was performed on thermally aged samples.
Regarding the dissolution rate, ENEPIG is available both with pure Pd and
with Pd containing P, which most likely will affect the dissolution rate.
I should stress that I have no own experience of ENEPIG, I am only
referring to what I have found in the literature.
Per-Erik Tegehall
Swerea IVF
References
Y. Oda, M. Kiso, S. Hashimoto, G. Milad, and D. Gudeczauskas, IMC Growth
Study on Ni-P/Pd/Au Film and Ni-P/Au Film Using Sn/Ag/Cu Lead Free Solder,
APEX 2006
Hugh Roberts, Sven Lamprecht, Christian Sebald, Mark Bachman, John
Osenbach, Kishor Desai, Ron Huemoeller, YoonHa Jung, Robert Darveaux,
Performance Evaluations of Surface Finish and Solder Alloy Configurations
for BGA Solder Joint Reliability, Pan Pacific 2009, pp. 248-256
Kuldip Johal, Hugh Roberts, Sven Lamprecht, Electroless Nickel /
Electroless Palladium / Immersion Gold Process For Multi-Purpose Assembly
Technology, SMTAI 2004, pp. 508-515.
Yukinori Oda, Masayuki Kiso, Seigo Kurosaka, Akira Okada, Kota Kitajima,
Shigeo Hashimoto, George Mila, Don Gudeczauskas, Study of Suitable
Palladium and Gold Thickness in ENEPIG Deposits for Lead-free Soldering
and Gold Wire Bonding, C. Uyemura and Corporation Ltd, Central Research
Laboratory, Osaka, Japan.
http://www.uyemura.com/images/library/ENEPIG-lead-free-solder-gold-wire-bonding-intermetallic.pdf
Chien Wei Lee, Liang Yi Hung, Chiang Cheng Chang, Yu Po Wang, C.S. Hsiao,
The Investigation of Intermetallic Compound Morphology Effect on the
Solder Joint Performance,
3rd International Microsystems, Packaging, Assembly & Circuits Technology
Conference, IMPACT 2008, pp. 263-266
: G.Milad, D.Gudeczauskas, G.Obrien, A.Gruenwald, A Study of the ENEPIG
IMC for Eutectic and LF Solders,
http://www.uyemura.com/pdfs/ENEPIG-IMC-Eutectic-LF-Solder-SMTA-2010.pdf
Chun-Hsien Fu, Liang-Yi Hung, Don-Son Jiang, Chiang-Cheng Chang, Y. P.
Wang, C.S. Hsiao, Evaluation of New Substrate Surface Finish: Electroless
Nickel/Electroless Palladium/Immersion Gold (ENEPIG), ECTC 2008
George Milad and Don Gudeczauskas, Soldering and Solder Joint Reliability
for Selected Surface Finishes with Lead Free SAC305 Alloy, SMTAI 2007
Bill Kao, Mustafa Oezkoek, Hugh Roberts, Pure Palladium in ENEPIG Surface
Finishes - Physical properties of the Pd deposition and their influence on
soldering and wire bonding, October 2010
http://www.atotech.com/data/pdf/papers_el/Pure_Palladium_in_ENEPIG_Surface_Finishes.pdf
-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För David D. Hillman
Skickat: den 12 mars 2013 23:24
Till: [log in to unmask]
Ämne: Re: [TN] IPC-7095C vs IPC-4556 ENEPIG for SnPb
Hi Kevin - I disagree with that statement in the IPC-7095C and didn't
realize it was there (otherwise I would have turned in a comment during
the draft efforts). I'll make sure to bring the topic back up in the 7095
committee as we start our next set of standards revision activities.
Rockwell Collins has successfully used ENEPIG surface finishes in tin/lead
and lead-free soldering applications for several years. We are in the
process of running another test sequence with one of the DOE legs using
ENEPIG surface finish so I should have an additional data set I can
present to the 7095 committee for review in regards to the wording you
detailed. Pd has very slow diffusion/dissolution characteristics in a
soldering process so you need to make sure you accommodate those
metallurgical reactions.
But - overall- the IPC-7095C represents a huge amount of work by the
committee with tons of new information that should be very useful to the
industry.
Dave Hillman
Rockwell Collins
[log in to unmask]
From: "Glidden, Kevin" <[log in to unmask]>
To: <[log in to unmask]>
Date: 03/12/2013 04:35 PM
Subject: [TN] IPC-7095C vs IPC-4556 ENEPIG for SnPb
Sent by: TechNet <[log in to unmask]>
Finally taking a few minutes to glance through some of the new IPC
releases...
I see a statement within IPC-7095C, specifically section 5.3.3.3, that
states ENEPIG is best suited for Pb-Free soldering, and that studies have
shown ENEPIG does not produce very reliable tin/lead solder joints, due to
the inability of Pd to alloy with lead.
I don't see any such warnings or statements in IPC -4556. Or am I missing
them? If this is true, it seems like it would be a major consideration
and would/should be included or mentioned in IPC-4556 Section 1.4.7
"Limitations of ENEPIG".
But, I could have it all wrong. So far all I have done is glance through
these new specs....
Kevin Glidden
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