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.
If you have received it in error, please notify the sender
immediately and delete the original. Any unauthorized use of
this email is prohibited.
----------------------------------------------------------------------------
--------------------
[mf2]
---------------------------------------------------
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 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
-----------------------------------------------------
|
