Just to put my two cents into the subject.
I have worked in both the metal finishing and the pcb industry for far too
many years.
Back in the day; all bright tin finishes were reflowed - for exactly the
reason of tin wiskering. One of the large avionics companies did their own
study and found that if they underlayed nickel as a barrier under tin; they
ran the problem of having a magnetic field under the tin. Their solution to
all this was to include 0.25 to 0.50% of lead in their tin plate.
Rudy; your right about the 40 microinches of immersion tin; but studies have
shown that when working with the military; since one of their process steps
is to bake all boards for an hour prior to assembling; 40 microinches is
insufficient, since baking at an hour will have the n-phase intermetallic
eat into the e-phase; and slowly creep into the immersion tin deposit -
depleting it.
What i have noticed over the last 4 to 5 years is that many of the board
manufacturers do not have a written procedure for their customers on how to
treat the boards prior to assemblying and this is causing severe problems in
the industry. Some even put the idents on at the end - this means the boards
get an additional 1hour bake at 300F before they are shipped out of the
plant. Then they wonder why the board assembler has problems assemblying the
boards.
My suggestion - before working with any board manufacturers - ask them
questions to understand if they truly understand why the chemical suppliers
coin all immersion processes as " Final Finish".
Rick Fudalewski
----- Original Message -----
From: "Dehoyos, Ramon" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, March 17, 2006 10:25 AM
Subject: Re: [TN] FW: [TN] Immersion Tin Specification
According to a plating Guru, ImSn includes some organic
components in the Tin plating that relaxes the stress. That may explain
the mitigating or elimination of whiskers. The plating is done electro
less in a chemical plating soup up to 0.05 mils or 50 millionths
thickness. This may be the way to go to eliminate or minimize whiskers
on component terminations.
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Thursday, March 16, 2006 5:16 PM
To: [log in to unmask]
Subject: [TN] 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
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