George-
Thanks for considering this issue.
Yes, I did review that UL paper prior to bringing this up on TechNet.
And I apologize for my misleading, non-technical language like
"decriminalize" and "pressure". But I think that, because of the title
of Section VIII of the report, which is about PCBs, that the iNEMI
report considers circuit boards a "component" covered by their
recommendations.
Please allow me to re-state my question in a more presentable form:
The recent iNEMI report contains phrases such as
from page 6, section IIIC: Finishes that Should Generally be Avoided
(in no particular order)
"9. Silver finishes are not prone to whisker growth in most
environments. However, rapid growth of silver dendrites or, in some
cases, silver whiskers may form in the presence of H2S (found in some
cases where the environmental air pollution contains SO2). Additionally,
users sometimes avoid silver finishes due to potential issues with
electromigration and solderability shelf life."
and from section VIII: Printed Circuit Boards:
"Of these surface finishes, immersion tin is susceptible to the
formation of pure tin whiskers and immersion silver is susceptible to
the formation of silver sulfide dendrites."
There are other sections in the paper which also place ImAg in a light
not commensurate with the published data I have reviewed.
Anyway, has anyone seen actual data which supports these statements?
The UL paper you and I both found suggests that ImAg is no more
susceptible to electrochemical migration (I hear you Bev!) than most
other finishes. The subject paper contains language which gives me the
impression some hydrogen sulfide tests were done with ImAg and the
results were of concern, but the only obviously relevant paper in the
reference area was
38 Chudnovsky, Bella, "Degradation of power Contacts in Industrial
Atmosphere: Silver Corrosion and Whiskers". Proceedings of the 48th IEEE
Holm Conference on Electrical Contacts, 2002
which I don't have ready access to, but I suspect it doesn't concern
ImAg.
Wayne
>>> "Wenger, George M." <[log in to unmask]> 12/18/2006 9:05:26
pm >>>
Wayne,
I'll take a stab at answering the two questions you raised and also
correct one of the statements you made.
You indicated incorrectly that you "know that UL recently
"de-criminalized" ImAg, primarily based on IPC pressure." The IPC
didn't pressure UL to "de-criminalize" immersion silver. IPC member
companies who had experience with immersion silver surface finish on
PCBs jointed the IPC 3-11g sub-committee along with UL participation
and
generated data that resulted in UL update the testing requirements
that
were being imposed on silver finishes. IPC and UL are organizations
that make specification changes based on data not pressure.
As for why iNEMI hasn't "de-criminalized" there was no reason for them
to "de-criminalize" immersion silver because they had never
"criminalized" it. If you look at the title of the paper written by
the
iNEMI Tin Whisker User Group it covers "iNEMI Recommendations on
Lead-Free Finishes for Components Used in High-Reliability Products".
This group concentrated on component finishes not board finishes. In
particular, if you look at Table 5 in their report that summarizes the
assessments of the individual members of the iNEMI Users Group
relative
to PCB finishes you will see that there are no tin whisker test
requirements for immersion silver.
As for papers on the electro-migration severity of immersion silver I
would start on the UL PCB site:
http://www.ul.com/pwb/silver.html
and then review the IPC 3-11g committee work.
Regards,
George
George M. Wenger
Andrew Corporation Wireless Network Solutions
Senior Principal FMA / Reliability Engineer
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 [Office] (732) 309-8964 [Cell]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Monday, December 18, 2006 3:48 PM
To: [log in to unmask]
Subject: Re: [TN] iNEMI Hi rel Pb-free finish report
Sorry. Here you go:
http://thor.inemi.org/webdownload/projects/ese/tin_whiskers/Pb-Free_Finishes_v4.pdf
Wayne
>>> [log in to unmask] 12/18/2006 2:57:21 pm >>>
Is the iNEMI 12/1/06 Pb-Free finish report published some
Wayne,
Is the iNEMI 12/1/06 Pb-Free finish report published somewhere?
Regards,
George
George M. Wenger
Senior Principle FMA / Reliability Engineer
Wireless network Solutions
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 (908)
546-4531
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Monday, December 18, 2006 2:50 PM
To: [log in to unmask]
Subject: [TN] iNEMI Hi rel Pb-free finish report
In this report (dated 12/1/06) there are several cautions about
Immersion Ag due to electro-migration issues, particularly in
sulfurous
environments.
I know that UL recently "de-criminalized" ImAg, primarily based on IPC
pressure. Why hasn't iNEMI?
Can anybody recommend a paper which explains the severity of this
electro-migration issue with respect to ImAg?
Thanks,
Wayne Thayer
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