It seems as I have to reply to the questions myself:
1. Immersion Tin has a typical cubical or prismatic organized
superstructure. Like the boards I got.
2. Tin whiskers are natural after ImSn processing.
3. But after soldering components, there is no risk any more.
http://www.atotech.com/fileadmin/pdf/papers/el/Immersion_tin_and_tin_whisker_growth.pdf
So, I've reduced my concerns to the question of copper diffusion through
both tin and solder mask and also what is the solderability of such
(badlooking in my opinion) pads.
Inge
----- Original Message -----
From: "Inge" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, September 07, 2009 5:06 PM
Subject: Re: [TN] Need clever comments
> Observation 1: I don't make that coincidence, I ask you all about a
> possible connection. Why? Because my experience is that one anomaly is
> often followed by more. Like lack of vitamins can cause many diseases. But
> my main worry is the anomalous solder pad look and also the presence of
> copper on the solder mask surface.
>
> Observation 2: in fact, if you study the conductor lines under strong
> light, there seems to be more copper colour than tin.
>
> Q2: Well, is pressfit positive or negative with nickel plating. Ericsson,
> one of the biggest telecom companies, have forbidden pressfit + nickel
> plating. And you say that Nortel have done it for years. Who is poppycock?
>
> Inge
>
> ----- Original Message -----
> From: "Bev Christian" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Monday, September 07, 2009 3:14 PM
> Subject: Re: [TN] Need clever comments
>
>
>> Inge,
>> Observation 1: How in the world can you make a connection between tin
>> whiskers and CAF?!!
>>
>> Observation 2: If copper is "penetrating" the solder mask, it makes me
>> wonder what it is doing to the tin overlayer! I would be concerned about
>> tin/copper intermetallic growing to the surface and oxidizing.
>>
>> Q2 Popppycock! Companies like Nortel and other put press fit connectors
>> into ENIG boards for years. Of course it is always a good idea not to
>> try
>> and put an elephant in a mouse hole. Make sure the pin and hole are
>> dimensional matched, the pin is put in straight and the proper force,
>> speed
>> and assembly apparatus are used to do it and that the end results are
>> cross-sectioned initially to make sure that it is right.
>>
>> Bev
>> RIM
>>
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
>> Sent: Monday, September 07, 2009 7:22 AM
>> To: [log in to unmask]
>> Subject: [TN] Need clever comments
>>
>>
>> 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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