Third, fourth ....next
My general rule/experience is that anything plated that is bright and shiny
is pretty but not necessarily solderable. Shiny is not an intrinsic property
of plated metals, but comes from all sorts of organic stuff - none of which
are solderable, and additionally may lead to out-gassing etc.
Plating Sn onto Ni instead of Cu is thought to reduce stress in the plating
and therefore whiskers. This is somewhat ironic: harder to solder Nickel
replaces easy to solder copper to avoid a problem which is introduced by the
finish intended to conserve solderability.
This finish is usually suggested because it suits a specific PCB supplier,
rather than to improve your manufacturing or in-service reliability etc
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: Thursday, July 01, 2010 12:14 AM
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
[log in to unmask]
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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