Hi Richard - there has been a bunch of papers showing that a pwb that do
not have nickel plating as part of its surface finish configuration, the
gold stays distributed in the solder matrix. However, the presence of
nickel plating changes the intermetallic phase energy of formation in
favor of gold containing intermetallic phases. The gold has been shown to
migrate back to the solder joint/pad interface and can sometimes result in
an gold embrittlement situation. The Agilent/Cal Poly paper in JEM does a
very good job of documenting that phenomena. As you detailed, the fact
that the nickel plating can cause that reaction means the users of ENIG
surface finishes need to understand their soldering process a bit more in
depth.
Dave
"Stadem, Richard D." <[log in to unmask]>
02/02/2012 10:59 AM
To
TechNet E-Mail Forum <[log in to unmask]>, "[log in to unmask]"
<[log in to unmask]>
cc
Subject
RE: [TN] ENIG thickness
A caveat to Dave's analogy below:
Even if you do use proper heat, dwell time, and solder volume, and achieve
very good homogeneity of the gold within the solder joint, over time the
gold will nucleate back to the intermetallic junction of the solder and
the pad (or whatever you are soldering to). This is what causes the
brittle nature of a gold-enriched solder joint. This is also why the
geometrical shape and other factors can cause even as little as 1% of
solder by volume to cause gold embrittlement in wire solder joints inside
of solder cups in connector pins, as an example. Don't assume you are
"safe" just because the gold volume is less than 2%, or 4%, or fully
homogenized, etc.
And don't assume a successful pull test shortly after soldering "proves"
there is no gold embrittlement, as it is a time-variable phenomena.
Only qualification through reliability testing will provide you with data
to bring to the party.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Thursday, February 02, 2012 10:36 AM
To: [log in to unmask]
Subject: Re: [TN] ENIG thickness
Hi folks - George beat me to the punch! Just to add to his good details -
the majority of the gold embrittlement cases you see published (and many
of others that are never published) are due to an incorrect soldering
process. The gold wants to dissolves at 100+ microinches per second but if
you don't use sufficient soldering heat, dwell time and solder volume, you
don't allow the gold to distribute itself equally throughout the solder
joint microstructure. There is also a good paper by the Agilent and Cal
Poly folks in the 2012 February issue of Journal of Electronic Materials
(JEM) on the how gold distributes itself in a solder joint when nickel
plating (just like what we have in ENIG) is present. The Bader reference
George mentioned is a must for everyone's files.
Dave Hillman
Rockwell Collins
[log in to unmask]
"Wenger, George M." <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
02/02/2012 10:21 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
"Wenger, George M." <[log in to unmask]>
To
<[log in to unmask]>
cc
Subject
Re: [TN] ENIG thickness
Victor,
If you go back to Wally Bader's paper that he published in The Welding
Journal when he was working for AT&T, which I refer to as "The Dissolution
Bible", you will see that gold dissolves in 450F SnPb solder at a rate of
117.9 microinches per second. Therefore the gold on an ENIG plated
surface with 4 to 5 microinches of gold will be gone in 0.03 to 0.04
seconds. I don't think you can realistically make the gold thick enough
so that it won't be totally consumed in a soldering process.
Regards,
George
George M. Wenger
Senior Principal Reliability / FMA Engineer
Andrew Corporation - Wireless Network Solutions
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 Office (732) 309-8964 Mobile
E-mail: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
Sent: Thursday, February 02, 2012 10:38 AM
To: [log in to unmask]
Subject: [TN] ENIG thickness
Fellow TechNetters:
At what ENIG thickness will the gold not be totally consumed by the
soldering process on a connector lead, LF solder joint. What happens
when the gold is not consumed. Will the joint structure be compromised.
What about the IMC formation. The SJ strength.
Victor,
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0 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 For additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0
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
For additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0
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
For additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0
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
For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
