No.Nickel barrier doesn't work with Immersion Tin.
Inge

----- Original Message ----- 
From: "Jack Olson" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, September 09, 2009 4:44 PM
Subject: [TN] Need clever comments


>I know I'm late to the game, but I can't resist asking this question:
>
>>From my experience, the tin is applied AFTER soldermask, so
> you have mask over bare copper, and tin over exposed copper.
>
> The tin in PHOTO2.JPG in the exposed area looks beautiful,
> so isn't the question (ignoring the whiskers for the moment)
> "How can bare copper erupt through the mask?"
>
> Unless I missed one of your previous posts, it seems to me that
> any speculation about copper poking through the tin finish is
> irrelevant. I'm only addressing Question 2 below, but you mentioned
> introducing a nickel barrier, and that will not be plated under the mask
> either, will it? only on exposed circuitry...
>
> just wondering,
> Jack
>
>
> -=-=-=-
>
>  *Subject:* Need clever comments *From:* Hernefjord Ingemar <
> [log in to unmask]> *Reply-To:* TechNet E-Mail Forum <
> [log in to unmask]>, Hernefjord Ingemar <[log in to unmask]> *
> Date:* Mon, 7 Sep 2009 13:21:54 +0200 *Content-Type:* text/plain
>
>
> Hi all, need some professional backup regarding MIL quality boards.
>
> Objects: FR-4 Class III double-sided multi-layer boards, populated
> with SOICS, BGAs,and a lot of passive components.
>
> Observation 1 : the non soldered board have lots of Tin whiskers on
> inside of the PTH barrel. My thought is this: if whiskers can grow
> long before the board is assembled, then ain't it likely that even CAF
> can be generated?  See photo 1.
>
> Observation 2:  Copper has somehow penetrated the solder mask. This
> can be found everywhere along the conductor traces. You need a very
> good light microscope and a SEM to see it. See photo 2.
>
> Board data: Copper with 0.8 micrometer Immersion Tin. No nickel
> barrier. Solder mask thickness not specified.
>
> Application: Typical MIL-883 environment
>
> Q1: What is your opinion about that thin Tin directly on copper? I
> dislike the concept. Copper is very mobile at high temperatures, and
> combined with humidity, there can be leakage currents and corrosion
> issues. Even if the boards are CCd, there is a risk with copper .
>
> Q2: I gave  the advice to introduce a nickel barrier, but our customer
> claimed, that they can't because of pressfit connectors and pressfit
> test pins on the board. Furthermore, they had heard that one cannot
> have nickel platings when pressfitting, because the nickel will crack
> and oxidize and cause electrical disfunction. Is this your opinion
> too? Are there any relevant testing behind such statements?
>
> Thanks in advance
>
> Inge
>
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