Jim, There was a paper by Toscano & Hillman (Rockwell) at the IPC Fall meeting that shows that even when it looks bad it performs well. They treated it with 85C/85%RH, salt fog or mixed flowing gas when in contact with Al, but it did not corrode, passed electrochemical migration AND had suitable contact resistance. regards, Bev Christian Research in Motion -----Original Message----- From: Marsico, James [mailto:[log in to unmask]] Sent: October 15, 2003 7:50 AM To: [log in to unmask] Subject: Re: [TN] ENIG solder joint embrittlement Not having any experience with immersion silver on PWBs, I have a question. In the past, silver plating was a problem because of tarnishing. Was this resolved? How? Jim Marsico Senior Engineer Production Engineering EDO Electronics Systems Group [log in to unmask] <mailto:[log in to unmask]> 631-595-5879 -----Original Message----- From: Wenger, George M. [SMTP:[log in to unmask]] Sent: Tuesday, October 14, 2003 7:57 AM To: [log in to unmask] Subject: Re: [TN] ENIG solder joint embrittlement Per-Erik, Let me start off by saying I hate the name "Black Pad" because it describes what a failure might look like but doesn't describe the type of failure or root cause. The historical Izod impact evaluations that were done on solder joints showed that a solder joint impact strength decreased by approximately 50% when the gold concentration was between 3 and 5%. Conservative reliability people usually use 3% as the gold embrittlement value and those who have to get product out the door have a tendency to say the value is 5%. With the introduction of fine pitch SM parts and BGAs the use of ENIG increased rapidly, so did the brittle fractures which got the name "Black Pad". Since the ENIG defect rate was low and random those investigating its cause tried to accelerate the defect level so that it could be evaluated. Unfortunately, when they began to use isothermal aging it appears as if they introduced another failure mode. Although the defects looked similar to "Black Pad" they were occurring with ENIG solder joints that had as little as 0.3 wt.% gold. When you do cross sectioning of isothermal aged solder joints made to ENIG you see intermetallic layers at the metallurgical interface to the copper. I've seen cross sections that sometime show what might be a AuNiSn IMC and at other times might be two layers AuSn and NiSn IMCs. I'm not a metallurgist and is some ways don't care what the IMCs are but I do care that they form and weaken the integrity/reliability of solder joints. I've given up waiting for a "Black Pad-Free" ENIG. We use ENIG on some boards where it makes sense but for the majority of our boards we use immersion silver Regards, George George M. Wenger (908)-546-4531 Reliability Engineer RF Power Amplifier Group Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 [log in to unmask] -----Original Message----- From: Tegehall Per-Erik [mailto:[log in to unmask]] Sent: Tuesday, October 14, 2003 3:24 AM To: [log in to unmask] Subject: Re: [TN] ENIG solder joint embrittlement George! I did not refer to the traditional form of gold embrittlement. There are numerous papers showing that gold may cause a new form of embrittlement when soldering to nickel surfaces. After soldering the gold will be find as AuSn intermetallic compounds evenly dispersed in the solder joint. However, after some time, that is no longer the case. Most of the gold will be found in a layer of AuNiSn IMC that is formed on top of the NiSn IMC layer on the nickel surface, which cause an embrittlement of the solder joint. The higher the temperature, the faster this will happen. At 150 degree C, you may have an ebrittlement of the solder joint after 24 hours and it might happen if the gold concentration is higher than 0.3 % and it is likely that you get that if you have a plating with electrolytic nickel/electrolytic gold on the component solder lands. For more information, se the following references: A. Eslambolchi, P. Johnson, M. Kaufmann och Z. Mei, Electroless Ni/Immersion Au Evaluation - Final Program Report, Electronic Assembly Development Center, Hewlett-Packard, Palo Alto, 1998. K. Zeng och K.N. Tu, Six Cases of Reliability Study of Pb-free Solder Joints in Electronic Packaging Technology, Materials Science and Engineering R, Vol. 38, 2002, sida 55-105. A. Zribi, R.R. Chromik, R. Presthus, K. Teed, L. Zavalij, J. DeVita, J. Tova, E.J. Cotts, J.A. Clum, R. Erich, A. Primavera, G. Westby, R.J. Coyle och G.M. Wenger, Solder Metallization Interdiffusion in Microelectronic Interconnects, IEEE Trans. on Comp. and Pack. Techn. Vol. 23, Nr. 2, 2000, sida 383-387. R. Darveaux, K. Banerji, A. Mawer och G. Dody, Reliability of Plastic Ball Grid Array Assembly, J.H. Lau (Ed.), Ball Grid Array Technology, McGraw-Hill, Inc., 1995, Kapitel 13. A.M Minor och J.W. Morris, Jr., Growth of Au-Ni-Sn Intermetallic Compound on the Solder-Substrate Interface After Aging, Metall. Mater. Trans, A, 31A, 2000, p. 789. http://www.lbl.gov/morris/private/papers.html <http://www.lbl.gov/morris/private/papers.html> A.M. Minor och J.W. Morris, Inhibiting Growth of the Au0.5Ni0.5Sn4 Intermetallic Layer in Pb-Sn Solder Joints Reflowed on Au/Ni Metallization, Journal of Electronic Materials, October 2000, Vol. 29, Issue 10, sida 1170-1174. http://www.lbl.gov/morris/private/papers.html <http://www.lbl.gov/morris/private/papers.html> Per-Erik Tegehall IVF, Sweden -----Ursprungligt meddelande----- Från: George Milad [mailto:[log in to unmask]] Skickat: den 14 oktober 2003 04:45 Till: [log in to unmask] Ämne: Re: [TN] ENIG solder joint embrittlement The firgure reported by Glazer from Hp for gold embrittlement was 3% and not 0.3%. The total amount of gold in ENIG if the new IPC 4552 specification is followed is less than 5 micro-inches or 0.12 microns. If one does the math, then it is evident that under these conditions "Solder Joint Gold Embrittlement" is a non issue for ENIG. Of course this is all on the board side and not the component. If there is an issue with component side separation, the target investigation should not be on ENIG leaving the true cause unidentified or addressed. Blaming the ENIG finish idiscrimanetly, and using the "black Pad" as a catch all leaves a lot of areas, where things could go wrong, unidentified and more important not corrected. Blaming the "Black pad" is prevalent. I often wonder how prevalent the ture cases of "Black Pad" are? George Milad Uyemura International Corp Chairman IPC Plating Commitee --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- ---------------------------------------------------------------------------- -------------------- This message is for the designated recipient only and may contain privileged, proprietary, or otherwise private information. 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