The experts I have listened to have stated the best way to eliminate tin
whiskers is to use leaded solder. That makes it kind of a conundrum.
Just my non-technical opinion.
Phil
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: Friday, July 08, 2005 11:02 AM
To: [log in to unmask]
Subject: Re: [LF] things like nemi tin whisker testing
Loa,
Although the Telcordia GR78Core document hasn't been updated in a long
time it does contain lots of good information about the best mitigation
process for tin whiskers (i.e., not use tin, or reflow it with hot oil,
or better yet poison it with the addition of >=2.0% Pb). All of the
mitigation processes being suggested now are just that mitigation not
elimination. In my previous employment we did work with Telcordia
(Bellcore back then) on the approval process to use Sn terminated
discrete ceramic chip capacitors. The measurements and analysis that
was done back in the early to mid 1990's showed that when using near
eutectic SnPb solder paste for SMT much of the Sn under the solder
fillet on discretes was poisoned with Pb from the solder paste.
Compositional measurements also indicated that the Sn above the solder
fillet had enough Pb present (I'm not a metallurgist so I'm not sure if
it got there by solid state diffusion, or some other mechanism) that tin
whiskers wouldn't be a problem. The real concern I have at present is
for Sn plated peripheral leaded IC packages because the solder fillets
stay close to the bottom of the gull wing lead. Even if there is a
large heel fillet the front surface of the gull wing leads don't see
SnPb solder and lots of the old Bell System tin whisker problems were
whiskers that grew from the shoulders of gull wing leads.
A big question on my mind right now is about the reported shut down of
the Millstone Nuclear Power plant in Waterford, CT that was reported in
the NY Times on July 5th (actually occurred April 17th). The article
makes it sound like the failure was due to a tin whisker. From what was
reported it is clear that a thin metallic filament on a circuit card was
the cause of the short circuit but until the analysis is completed and
reported I think the industry shouldn't jump to the conclusion that the
failure was a tin whisker even though the probability is high that it
was. I just wish the analysis was completed and the information was
available because until it is there will be lots of speculation.
Regards,
George
George M. Wenger, Reliability Engineer
Andrew Corporation
40 Technology Drive
Warren, NJ 07059
(908) 546-4531 or (732) 309-8964 (Cell)
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of ALLEN, LOA
Sent: Friday, July 08, 2005 10:02 AM
To: [log in to unmask]
Subject: [LF] things like nemi tin whisker testing
Topic changing
Thread formerly known as -
"RE: [LF] Banned substances 5 out of 6 and not all 6 out of ???"
John/Listservers,
We too are in the telecommunications world and have no intention of
rushing into the Pb-free arena - but as you are aware, we are being
thrown into the arena, like it or not (Pb component availability).
Currently, our biggest concern has been the identification of Pb-free
comps (other than Sn) to forewarn our CMs of special mfg needs/attention
- we are not using any Bi that we are aware of. However, you mentioned
the tin whisker warning - as long as we are still using a 63/37 SnPb
paste for assembly we haven't been too concerned. For several years,
many chip mfrs (SMT caps & resistors) have used Sn termination plating
without letting the general public know of the switch. Are you eluding
this is a potential for tin whisker failures? Is the SnPb paste not
enough to eliminate tin whisker?
Thanks in advance,
Loa
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Friday, July 08, 2005 1:44 AM
To: [log in to unmask]
Subject: Re: [LF] Banned substances 5 out of 6 and not all 6 out of ???
Welcome to the world of telecommunications.
Many companies in this industry will NOT allow supplier companies to
remove the leaded solder since it has a good reliability which is
proven. Thus the term 5/6 used to describe this industries exemption
under the RoHS annex paragraph 7c.
Unfortunately with most other componentry heading down the lead free
trail, it is difficult to maintain the reliability when customers insist
on a leaded soldering system.
Component engineers should be very diligent in these situations to check
for things like nemi tin whisker testing on alternate components; the
use of things like bismuth as in tin bismuth plating as used on memory
devices. Also use of lead free BGA's in a leaded assembly ............to
name but a few........will all potentially reduce relibility of
electronics assemblies.
John
------------------------------------
Avanex
John Burke
Senior Manager RoHS Compliance
[log in to unmask]
40919 Encyclopedia Circle
Fremont
CA 94538
tel: 510 897 4250
fax: 510 979 0189
mobile: 510 676 6312
------------------------------------
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]]On Behalf Of Martin Cook
Sent: Friday, July 08, 2005 1:24 AM
To: [log in to unmask]
Subject: Re: [LF] Banned substances 5 out of 6 and not all 6 out of ???
5 out of 6 using Sn/Pb solder & Pb-Free components is going to be
painful when building 6 out of 6.
5 out of 6 using Sn/Pb solder & Sn/Pb components turns into a
nightmare!!!!!!!!!!
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]]On Behalf Of MA/NY DDave
Sent: 08 July 2005 04:53
To: [log in to unmask]
Subject: Re: [LF] Banned substances 5 out of 6 and not all 6 out of ???
Hi Ken, IPC LF Listservers,
Go back and read a post of 31May where John Burke participated.
The below link should get you to his note and then scroll backwards for
more dialog.
http://listserv.ipc.org/scripts/wa.exe?
A2=ind0505&L=leadfree&P=R15412&D=0&H=0&I=-3&O=T&T=0
Yours in Engineering, Dave
YiEngr, MA/NY DDave
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