At 11:52 AM 9/10/2009, Dwight Mattix wrote:
>At 10:45 AM 9/10/2009, Stadem, Richard D. wrote:
> >Or hanging around the Laundromat with his .44 automatic.
>
>.44 automatic? I didn't take Steve for a Desert Eagle sort of guy.
On second thought, weren't you a P-3 sailor?
In which case I'd empathize with any Mall Cop type frustrations and
resultant compensating behaviors. Maybe we could all pass the hat
and help raise funds for a tactical wheelbarrow to go with the Desert
Eagle and Tactical Segway.
> >-----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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