Inge has a clean, lower caliber sense of humor.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Maxwell
Sent: Thursday, September 10, 2009 10:59 AM
To: [log in to unmask]
Subject: Re: [TN] Need clever comments
It should be a 45 automatic
> Or hanging around the Laundromat with his .44 automatic.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
> Sent: Thursday, September 10, 2009 11:25 AM
> To: [log in to unmask]
> Subject: Re: [TN] Need clever comments
>
> I will post a handful SEM images to Steve, so you get an idea what
it's
> all
> about.
> It may take a while, because he is probably on the market place to buy
> curtains and wallpaper
> for his new appartment. Or jogging. Or having a drink on the balcony.
> /Inge
>
>
> ----- Original Message -----
> From: "Inge" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, September 10, 2009 5:10 PM
> 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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