Inge,
You have Paul's good comments as well ...
Regarding not being smarter than a polliwog, please refer to recent string
on PTH plating [the lack thereof] anomaly.
Yes, there appear to be a few tacks in the box that are indeed NOT very
sharp! :-)
Hopefully, this does not include your supplier, but ....
Steve C
-----Original Message-----
From: Inge [mailto:[log in to unmask]]
Sent: Thursday, September 10, 2009 11:40 AM
To: TechNet E-Mail Forum; Steven Creswick
Subject: Re: [TN] Need clever comments
Good idea, but presupposes that someone is not brainier than a polliwog.Can
that be?
/Inge
----- Original Message -----
From: "Steven Creswick" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, September 10, 2009 5:21 PM
Subject: Re: [TN] Need clever comments
> Inge,
>
> Could the copper 'contamination' have been a transfer of copper caused by
> someone placing a non-masked board, with exposed copper, in contact with
> the
> surface of your board's solder mask?
>
> Maybe during shipment, etc.?
>
> Steve C
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
> Sent: Thursday, September 10, 2009 11:11 AM
> To: [log in to unmask]
> Subject: Re: [TN] Need clever comments
>
> Jack &Paul, FYI.
>
> Today I had a close look at the cross sections. What I found was this:
>
> 1. The Tin plating was done AFTER solder mask (Jack was right)
> 2. The solder mask was very uneven, thickness between 5um and 25 um.
> 3. Despite the corrupted surface, the solder mask is homogenous, no
> vertical
>
> cracks found.
> 4. The copper that I found earlier on top of the conductor, i.e. on the
> solder mask, that copper had no connection with the conductor copper.
> Which
>
> means that these contaminations had NOT migrated through the solder mask.
> 5. I can still not figure out from where the copper contaminations come.
>
> So, all that remains is the question about the copper contaminations tha
> embedded in the very surface of the solder mask. I have to adjust my
> report
> and resend it to our customer and the board maker.
>
> Thanks to your critisism, I can now redo the analys, starting from a more
> correct standpoint.
>
> Your are great!
>
> /Inge
>
>
>
>
> ----- Original Message -----
> From: "Inge" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Wednesday, September 09, 2009 8:09 PM
> Subject: Re: [TN] Need clever comments
>
>
>> Jack,
>>
>> SMOBC is the common industrial standard, as you pointed out, however,
>> there ARE some fabricators that apply the solder mask after Tin/Lead-ing
>> the copper traces. The later method has an obvioius disadvantage, see
>> below quoted from an article written by US Environmental Agency:
>>
>> " This method predominates for several reasons. Copper is a surface that
>> lends itself to rigorous cleaning, which is essential for solder mask
>> adhesion. Tin-lead under solder mask will liquefy during soldering and
>> may
>
>> cause the mask to blister and peel. The hot air solder leveling process
>> generally produces less waste water and introduces less lead into the
>> waste water stream than tin-lead plating and reflow. Despite these
>> advantages, well-known disadvantages also exist. The shelf-life of hot
>> air
>
>> solder leveled circuits is short and solder thicknesses on pads and hole
>> barrels is notoriously difficult to control. For these reasons, a small
>> minority of specifications continue to call for tin-lead plate and reflow
>> or other alternati air solder leveling, nomenclature screening, and
>> finally, gold edge plating if necessary. "
>>
>> I think that is what happened to our boards....." cause the mask to
>> blister and peel"...
>>
>> Another paper describes Tin under solder mask this way:
>>
>> " Facility F initially was concerned with the soldermask breakdown where
>> the Tin leaches underneath the soldermask....etc"
>>
>> Quoted from EPA (United States Environmental Protection Agency.
>>
>> When I started the investigation (had just some hours to spend before
>> reporting the result!), I was fully convinced that these boards were
>> SMOBC, but our customer said they used tinning before soldermask. I have
>> asked for a confirmation from the board fabricator, but got no answer.
>>
>> Thanks for your comment, good critics.
>>
>> 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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