At 08:40 AM 9/10/2009, Inge wrote:
>Good idea, but presupposes that someone is not brainier than a polliwog.Can
>that be?
Only remedy for Pollywogs is a trip before King Neptunes court.
We Shellbacks can tell when we are in the company of polliwogs. It's
apparent by the foul stench they emit.
>/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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