Hi Mel! I agree with you but I also have the other reality of needing to
progress forward in a logical manner. I have spent a considerable amount of
time looking at the proposed mechanism each of the immersion tin suppliers
reported, looked at metallographic and SEM data for the finishes, and ran
the most currently accepted "acceleration" methodology. Can I say with 100%
certainty that I have found all of the ghosts haunting the machine? Nope,
but I have went the fullest extent possible, using data/analysis, to
understand the risk. The good news is that I believe (IMHO) the source
cause for tin whiskers (based on Mike Toben (Shipley) and Rob Schetty
(Technic)) has been documented (both Mike and Rob made presentations at the
IPC Fall meeting in Orlando). There is a NEMI group working on the
development of an industry standard acceleration method and their efforts
look promising. I am hoping that they will be able to deliver a method
which gives us the "long term" prediction tool we need.
Dave Hillman
Rockwell Collins
[log in to unmask]
"Mel Parrish" <[log in to unmask]> on 04/04/2002 04:11:06 PM
To: "TechNet E-Mail Forum." <[log in to unmask]>,
<[log in to unmask]>
cc:
Subject: RE: [TN] Tin whiskers and immersion tin coatings
Dave and all,
From what I have seen, you are certainly correct that the plating process
contributed to the growth of whiskers. What I do have concern for is the
inability to accelerate the growth of whiskers beyond the environment that
very closely parallels operation for electronics. Soo how do you test for
whisker growth tendency beyond plating and waiting for four or five years
to
see if it grows whiskers. Standard cycling and temperature environments
only
contribute to delay whisker formation. I think that the jury is still out
on
slightly elevated humidity impact. There are some very high end tests that
can compare surface tensions for compressive stresses which cause whisker
formation but I doubt if the plating shops are doing that.
I guess that I'm hoping that someone has a way to predict the tendency to
grow whiskers beyond what I've seen so far. Our committees looking at this
haven't found one yet.
Any revelations would be appreciated.
Mel Parrish
Soldering Technology International
102 Tribble Drive
Madison, AL 35758
256 705 5530
256 705 5538 Fax
[log in to unmask]
www.solderingtech.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dave Hillman
Sent: Thursday, April 04, 2002 10:16 AM
To: [log in to unmask]
Subject: Re: [TN] Tin whiskers and immersion tin coatings
Hi Bev! We have been using immersion tin surface finish for about 1 year
and have had no issues with whisker growth. During our qualification
testing the whisker issue was a very important test matrix question and we
requested the all of the immersion tin suppliers furnish their tin whisker
data. The immersion tin chemistry suppliers (well, at least one for
certain!) appear to have successfully engineered chemistries which do not
permit whisker growth. My recommendation would be to work closely with the
pwb fabricator and/or the chemistry supplier to understand what they are
doing to eliminate whisker growth. Now if you want to really get nervous
just think about the component fabricators who are choosing to use matte
tin as a component lead finish - let's hope they have done their
homework/testing.
Dave Hillman
Rockwell Collins
[log in to unmask]
Bev Christian <[log in to unmask]>@ipc.org> on 04/02/2002 05:40:04 PM
Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
to Bev Christian <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
To: [log in to unmask]
cc:
Subject: [TN] Tin whiskers and immersion tin coatings
Technetters,
To a certain extent I am aware of the work the NEMI tin whisker task force
and various connector/component manufacturers are doing about 100% tin
coatings. But I am still left with several questions whose answers I have
missed or questions that have not been addressed. So... here goes - the
immersion tin coating are for SMT pads that are going to be soldered. What
are people doing about test points? Are there stencil openings to put
solder
on these pads as well? Or are these pads left unsoldered? Has anyone
carried out any testing with regards to the tendency of these materials to
grow/not grow whiskers? Or do the organics in the coating completely kill
that possibility?
regards,
Bev Christian
Research in Motion
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