I'll gladly join this sage disennters list.
Run, don't walk, away from electroplated bright tin. You might get lucky with a particular batch of plating solution one day, and not so lucky the next. Plating chemistries can change (what organics are included) and unfortunately, the manufacturers do not tell us what's in the bath, nor will the plater know what's in it.
Since the application is for a power bus, be sure to review an item on the NASA website that deals with your application.
The following anecdote describes the observations of tin whisker formation on tin-plated copper bus bars installed in power distribution equipment at a large paper mill in Sweden. The tin whiskers are suspected to have contributed to the formation of metal vapor arcs within the equipment resulting in significant damage and downtime on at least three separate occasions (1997, 2000, 2009) at this mill.
http://nepp.nasa.gov/whisker/anecdote/2009busbar/index.html
Bob Landman
H&L instruments, LLC
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Edwards
Sent: Wednesday, June 30, 2010 7:28 PM
To: [log in to unmask]
Subject: Re: [TN] Bright tin
Make it a third...
Had to deal with the finish dewetting problems by setting use-by, store-in and bake-in-N2 rules for using the PCBs....
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: Wednesday, June 30, 2010 4:14 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]>
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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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