I met a scientist from the Ministry of Defense in Israel at the latest PERM symposium on lead free issues. He told me that he routinely uses immersion tin to generate whiskers for study.
Again, I would caution you that it depends on the chemistry of the plating bath as is discussed in this paper
http://www.atotech.com/data/publications/pcb/Immersion_Tin-Kinetics_of_Whisker_growth.pdf
And http://www.empf.org/empfasis/2006/mar06/geia-tin_whiskers.html where it's stated "The first factor is the tendency of tin whiskers to grow for extremely long periods of time, long past the obsolescence timeframe (and replacement) of commercial electronics. Figure 4-2 is an electron microscopic picture of a circuit board surface having immersion tin plating after 3 months of room temperature storage onsite at the EMPF. Note the small, 10 to 20 micron tin whiskers that are present. These whiskers are too small to be a serious risk, even to fine pitch circuitry. Figure 4-3 shows the same sample after 30 months of storage (perhaps a long time for a commercial application, but a short time for a DoD application) showing some tin whiskers that have grown to over 100 microns, long enough to electrically short closely spaced modern electronic circuits."
When we rennovated our 1878 Victorian home we installed tin plated ceiling panels in place of the sheetrock. I just checked a sample of the tin (over steel) that was in our attic here in New Hampshire and found, to my surprise, whiskers sprouting from the plating. The finish is not bright but is more of a semi-bright finish (the sample was sent to us in 2001).
Bob Landman
H&L Instruments, LLC
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Cedric ORAIN
Sent: Thursday, July 01, 2010 8:35 AM
To: [log in to unmask]
Subject: Re: [TN] Bright tin
I will definitely choose another finishing. What do you think of immersion tin as regard to the screwed terminals that have to carry high current? Is the pads are likely to oxydised and have lower conductivity?
-----Message d'origine-----
De : Stadem, Richard D. [mailto:[log in to unmask]] Envoyé : jeudi 1 juillet 2010 14:15 À : TechNet E-Mail Forum; Wenger, George M.; Cedric ORAIN; 'R Sedlak'; [log in to unmask] Objet : RE: [TN] Bright tin
And I'll be the third, but that is irrelevant. Let's try to help Orain with the original issue; what is the best finish for his particular product?
Orain, is this a new PWB, or were you using a same/similar design before with good results?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: Wednesday, June 30, 2010 6:14 PM
To: [log in to unmask]
Subject: Re: [TN] Bright tin
Dave,
I'll be the second dissenter right behind you.
Regards,
George
George M. Wenger
Senior Principal FMA / Reliability 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 David D. Hillman
Sent: Wednesday, June 30, 2010 5:27 PM
To: [log in to unmask]
Subject: Re: [TN] Bright tin
Hi Rudy - I guess I'll be the voice of dissent but I would run as far away from bright tin as fast as possible. The industry studies demonstrating bright tin's ability to initiate and growth tin whiskers making a plated object look like a chia pet are numerous. Additionally, the co-deposited organic materials in a bright tin plated finish typically result in outgassing during soldering resulting in poor solder joints of questionable integrity. Steve G. had a picture several months back of the result of trying to solder a bright tin plated connector. Finally, bright tin has poor solderability shelf life issues (as you detailed) due to oxidation issues. I recommend not allowing the use of bright tin on pwbs.
Dave Hillman
Rockwell Collins
[log in to unmask]
R Sedlak <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
06/30/2010 01:05 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to R Sedlak <[log in to unmask]>
To
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cc
Subject
Re: [TN] Bright tin
Cedric:
Bright Tin is definitely electroplated, and as such can be much thicker
than the more common immersion Tin, however, since it is electroplated, it
covers the top of the pad, and there may be exposed Copper on the sides of
the pad.
Bright Tin is high in organics, which should minimize, but not eliminate,
Tin whiskers.
Nickel is normally not used under Bright Tin, although it MIGHT help shelf
life. Shelf life of Bright Tin finish is more controlled by oxide
formation on surface of Tin, rather than by intermetallic formation,
because the Tin is usually so thick.
Hope this assists.
Rudy Sedlak
RD Chemical Company
--- On Wed, 6/30/10, Cedric ORAIN <[log in to unmask]> wrote:
From: Cedric ORAIN <[log in to unmask]>
Subject: [TN] Bright tin
To: [log in to unmask]
Date: Wednesday, June 30, 2010, 10:03 AM
Hello all,
I've been proposed Bright Tin as PCB finishing. It is the first time I've
heard about this plating for PCB.
Is someone is familiar with this process and could expose drawbacks and
benefit?
Do you confirm that it is an electroplating process? Do I need to specify
a
Nickel barrier or something lie that underneath the tin layer? Is the
thickness of tin is critical and has to be monitored carefully?
I'm also concerned about tin whiskers with bright tin as it as been banned
from the plating of connectors and components due to its propensity to the
growth of whiskers.
Ok, it's a lot of questions! I just want to be advised on what is
important
to know about that subject.
Thanks in adavance for your bright advice.
Cedric ORAIN
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