Look what MULTEK say about Immersion Tin, confirmation on what I said in
recent mails. Go to page 71.
Neither they use nickel barrier.
/Inge
http://www.dnu.no/arkiv1/multek_20060914_DFX.pdf
----- Original Message -----
From: "Inge" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, September 07, 2009 6:57 PM
Subject: Re: [TN] Need clever comments, closed .
> Finally, I think I found a reasonable answer on the last issue, that was a
> copper rich and deteriorated solder mask over the copper traces:
>
> 6. Ingredients in the immersion process can be aggressive to the solder
> mask. Also, too rough a copper will cause insufficient homogenity and
> thickness of the solder mask. It's important that the solder mask matches
> the chemistry of the immersion process, as well as the requirement on
> copper planarity be fulfilled. So, the copper went through the (too) thin
> tin layer and found its way also through the destructed solder mask.
>
> 7. The conformal coating, that we apply, will seal the solder mask, and
> the board will work for period of xx months. If our customer pay us, we
> will do tests to decide this time level.
>
> With other words, the board manufacturer has not been very accurate and
> our customer did not perform any Incoming Inspection on these boards.
>
> Thank you for contributing.
>
> Inge
>
> ----- Original Message -----
> From: "Inge" <[log in to unmask]>
> To: "TechNet E-Mail Forum" <[log in to unmask]>; "Inge"
> <[log in to unmask]>
> Sent: Monday, September 07, 2009 5:52 PM
> Subject: Re: [TN] Need clever comments
>
>
>> OK, I think I've found more answers on the rest of my questions:
>>
>> 4. You never use nickel barrier for Immersion Tin, because the Immersion
>> Tin with nickel barrier won't readily form binding intermetallics to the
>> barrier, while Tin in direct contact with Copper creates strong and
>> stable intermetallics.
>> 5. What I've seen is probably the result of too thin ImSn. The below
>> article clarifies, that there is a dramatic thickness level, under which
>> the copper makes the bond pads unsolderable. If the ImSn is dense enough
>> and thicker than 1um, there ought to be no concerns about solderability,
>> granted that you don't pass fresh date.
>>
>> http://www.ecitechnology.com/articles/Surface_Evaluation_of_the_Immersion_Tin_Coatings_via_Sequential_Electrochemical_Reduction_Analysis_(SERA).pdf
>>
>> The remaining question is now only the copper on top of the solder mask.
>>
>> Sorry for rushing, but I have just one day to decide what to report.
>>
>> Inge
>>
>>
>>
>> ----- Original Message -----
>> From: "Inge" <[log in to unmask]>
>> To: <[log in to unmask]>
>> Sent: Monday, September 07, 2009 5:27 PM
>> Subject: Re: [TN] Need clever comments
>>
>>
>>> 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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