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
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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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