The all inclusive answer...wait for it..."IT DEPENDS"
Component leads have bends and cut ends and potentially scrapes and
other notorious stress points that tin whiskers could emanate from.
However, it depends what you do with your PWB whether you are inducing
stress points in that surface as well.
We often screw things down to our PWB's. Shields, heatsinks, etc.
Those points where the washer/screw make contact with the surface could
potentially become stresspoints that whiskers might spontaneously erupt
from...
But bright tin has always been reported as more likely to whisker than
matte tin in everything I've read, and isn't Immersion tin sort of a
version of matte tin?
Just my 1.86cents.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: 16-Mar-06 4:24 PM
To: [log in to unmask]
Subject: Re: [TN] Immersion Tin Specification
To add to my email below, I have an application where a transmitter
assembly will be running in the area of 2 gigahertz. Immersion tin
finish was proposed as a cheaper alternative to immersion silver. My
concern was that if even a very small amount of tin whisker migration
occured, it would act as a deflector on the signals in the RF circuit,
much like an antenna. The PWB vendor stated that there are some
immersion tin finishes that provide no danger of whisker growth, and
stated I would have more problems from tin whiskers on the component
terminations than I would from the PWB finish. I find this highly
unlikely. Any input on this?
-----Original Message-----
From: Stadem, Richard D.
Sent: Thursday, March 16, 2006 4:16 PM
To: 'TechNet E-Mail Forum'
Subject: FW: [TN] Immersion Tin Specification
-----Original Message-----
From: Stadem, Richard D.
Sent: Thursday, March 16, 2006 4:12 PM
To: 'Vladimir Igoshev'
Subject: RE: [TN] Immersion Tin Specification
My apologies, Vladimer. I double checked my information. I have a finish
provider whose documentation for a bright tin finish on the PWB claims
it is "whisker-free". That confused me. I went back over the references
I have (NEMI report and "Tin Whiskers: Attributes and Mitigation" by J.
Brusse, G. Ewell and J. Siplon, and other references)and they support
what you are saying. The finish vendor apparently recommends putting the
bright tin over a nickel base, which supposedly mitigates the whisker
formation. Does this make sense?
There is so much conflicting information amongst those providing tin
finishes for components versus tin finishes for circuit boards it is
hard for me to keep it all straight.
-----Original Message-----
From: Vladimir Igoshev [mailto:[log in to unmask]]
Sent: Thursday, March 16, 2006 3:52 PM
To: Stadem, Richard D.
Subject: Re: [TN] Immersion Tin Specification
Richard,
Can you send me the referrence? Unless I'm completely confused, that is
not what I've been hearing.
Vladimir
Sent from my Blackberry Wireless
Vladimir Igoshev, 519-888-7465 ext.5283
----- Original Message -----
From: Stadem, Richard D. <[log in to unmask]>
To: Vladimir Igoshev
Sent: Thu Mar 16 16:47:42 2006
Subject: RE: [TN] Immersion Tin Specification
Thank you. Then why is it reported that matte tin has a greater tendency
to incur tin whiskers? Would it be because of a higher stress factor in
the grain?
-----Original Message-----
From: Vladimir Igoshev [mailto:[log in to unmask]]
Sent: Thursday, March 16, 2006 3:43 PM
To: [log in to unmask]; Stadem, Richard D.
Subject: Re: [TN] Immersion Tin Specification
As far as I know, immersion tin is better than mette and of cause bright
ones
Vladimir
Sent from my Blackberry Wireless
Vladimir Igoshev, 519-888-7465 ext.5283
----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Thu Mar 16 16:39:34 2006
Subject: Re: [TN] Immersion Tin Specification
Better than what? Better than it used to be? Could you clarify, as I am
wondering what you mean by that. Thanks.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Vladimir Igoshev
Sent: Thursday, March 16, 2006 3:29 PM
To: [log in to unmask]
Subject: Re: [TN] Immersion Tin Specification
Ramon,
Immersion Tin is MUUUUUCH better in terms of whiskering.
Vladimir
Vladimir Igoshev, Ph. D.
Manager, Metallurgical Lab
Research in Motion
451 Phillip St.
Waterloo, ON, N2L 3X2
Voice: (+1) 519-888-7465, ext. 5283
Fax: (+1) 519-886-0863
E-mail: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dehoyos, Ramon
Sent: Thursday, March 16, 2006 4:12 PM
To: [log in to unmask]
Subject: Re: [TN] Immersion Tin Specification
John:
Just curious, what is the tin plating going to be used
on? Thin Tin plating produces whiskers, which can be a nightmare.
Thicker Tin plating helps as a whisker mitigating factor. These whiskers
have shot down a nuclear power plant and caused space craft failures.
Tin plating can very problematic. Whiskers can grow in days or take
years.
Regards,
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of R Sedlak
Sent: Thursday, March 16, 2006 4:01 PM
To: [log in to unmask]
Subject: Re: [TN] Immersion Tin Specification
John: Generally accepted goal is one micron, or 40 microinches,
thickness.
You essentially never have to worry about it being too thick, and
thickness of less than 75% of that value should raise eyebrows...
Rudy Sedlak
RD Chemical Company
John Parsons <[log in to unmask]> wrote: IPC have graciously
provided us (the industry) with specifications for ENIG
(IPC-4552) and Immersion Silver (IPC-4553), is there a similar
specification Immersion Tin (white tin)? If not, is there a generally
accepted specification for material thickness?
John Parsons
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
