Thanks. This may be a dumb question, but is there a difference between
"promote" and "susceptible to"?
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Friday, March 24, 2006 2:09 PM
To: [log in to unmask]
Cc: [log in to unmask]
Subject: Re: [TN] Tin Whisker Mitigation
Hi Kevin! As a user of immersion tin and a member of the IPC-4554 committee,
I can tell you first hand that immersion tin chemistry formulations do not
promote tin whisker growth. However, all tin surfaces (e.g. pwbs,
components, sheet metal, etc.) should be assessed for tin whisker risk. Not
all immersion tin surface finish chemistries are created equal.
Dave Hillman
Rockwell Collins
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Kevin Glidden
<[log in to unmask]
COM> To
Sent by: TechNet [log in to unmask]
<[log in to unmask]> cc
Subject
03/24/2006 11:16 Re: [TN] Tin Whisker Mitigation
AM
Please respond to
[log in to unmask]
om
I believe immersion tin DOES promote whiskers, although not at the same
level as electrolytic tin. Check IPC-4554, especially Appendix 6. "A
potentially significant source for whisker formation are stresses induced
from formation of CuSn IMCs....Whiskers have grown on immersion tin
conductive features. To date, these whiskers have appeared at ambient
conditions..."
As for using cc for mitigation, it has also been found that whiskers will
still grow under (and even penetrate) coating. Check NASA paper "Effects of
Conformal Coat on Tin Whisker Growth".
Regards,
Kevin
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
Sent: Friday, March 24, 2006 11:34 AM
To: [log in to unmask]
Subject: Re: [TN] Tin Whisker Mitigation
Dewey:
I hear you loud and clear. In the near future thanks to some
crazy fellows that want to save the earth.... We may have to go that route
per customer request. Other choices ensure that the Tin finish is Matte,
bigger grain, instead of bright tin ( do not know yet how to verify that),
have at least 3% Pb or 3-5% Bi( use of XRF) , CC assembly, annealing
components, reflow assembly, immersion Tin finish.... My understanding of
Immersion tin is that it does not promote Whiskers. The problem that I know
about this finish, ImSn, is that it is too thin and IMC form to make it
unwetable.
Thanks for your sharing,
Regards,
Ramon
-----Original Message-----
From: Whittaker, Dewey (AZ75) [mailto:[log in to unmask]]
Sent: Friday, March 24, 2006 10:39 AM
To: TechNet E-Mail Forum; Dehoyos, Ramon
Subject: RE: [TN] Tin Whisker Mitigation
Ramon,
Yes.
Don't do it and spare yourself the cruel and unusual punishment.
Depending on your customers and critical end-use applications, the amount of
effort to do this and control it is incredible. It can be done, but it
extracts a heavy toll. Even meager efforts in-house with chips is a waste of
dough( now class did you catch the joke? Toll house morsels = Chips(
chocolate) = waste of dough. Good you earned your chocolate chip cookie).
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
Sent: Friday, March 24, 2006 8:18 AM
To: [log in to unmask]
Subject: [TN] Tin Whisker Mitigation
Hello TechNetters:
Does anyone know of companies that are replating parts with Sn63
and reballing BGAs? Could any one share their experiences in
doing this effort? Things such as: extra time needed, cost,
reliability.......
Regards and TIA,
Ramon Dehoyos,
410.552.2210
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