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November 2002

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Subject:
From:
Gaby Bogdan <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 26 Nov 2002 02:52:51 +0200
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Thanks Dave
 As always prince valiant-but Diet coke-I begin to doubt...
When you come back from supper- What about the differences between immersion
silver coating processes?
What should I look for?
Tested solderability from Two suppliers- both were OK, but then-x-rayed
BGA's on the same board cat.no.- and PUFF! one had voids staying on the
circuit pads SOOOOOO big, the other-just very few.Did them on a mixed batch
concommitent.
Gaby
----- Original Message -----
From: <[log in to unmask]>
To: <[log in to unmask]>
Cc: <[log in to unmask]>
Sent: Tuesday, November 26, 2002 1:46 AM
Subject: Re: [TN] Immersion Tin


>
> Hi Gaby! The Achilles heel of all tin finishes - immersion tin included -
> has been its thermal degradation characteristics. Thermal excursions cause
> two degradation mechanisms: 1) the growth of surface oxidation - as the
SnO
> oxide transforms to SnO2 oxide the solderability goes downhill very fast;
> 2) the growth of copper/tin intermetallic phases - if the copper/tin
> intermetallic phases (especially the Cu3Sn phase but also the Cu6Sn5
phase)
> reach the surface and become oxidized then the solderability goes to zero.
> Remember - the more active the flux system you use the less impact both
> these mechanism have in your production process.  What differentiates the
> various available immersion tin chemistries from each other is how each of
> the individual chemistry suppliers formulates their immersion tin bath to
> account for these two degradation mechanisms.  I agree with you on
> procurement - if you need an immersion tin finish which will withstand
> multiple thermal excursions then you should expect to pay more and have
> fewer potential chemistry supplier choices. If you only need one thermal
> excursion pass then more immersion tin possibilities exist. The needs of
> the process should be matched to the characteristics of the surface finish
> - and both the pwb fabricator and pwb user need to work together to meet
> those goals. Enough said - I'm off to find a Diet Coke for supper!
>
> Dave
>
>
>
>
> Gaby Bogdan <[log in to unmask]> on 11/25/2002 06:19:51 PM
>
> To:    "TechNet E-Mail Forum." <[log in to unmask]>,
>        [log in to unmask]
> cc:
>
> Subject:    Re: [TN] Immersion Tin
>
>
> Dave,
> What is the cause of "degradation"?
> Do you mean that this process is not the same from one supplier to the
> other
> ? And  even more- that the procuring department should buy boards from
> different suppliers according to their proven performance for each
> finishing
> process?
> By the way- that's what we try to do.
> Gaby
> ----- Original Message -----
> From: "Dave Hillman" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Monday, November 25, 2002 11:53 PM
> Subject: Re: [TN] Immersion Tin
>
>
> > Hi Yannick! Not all immersion tin chemistries are created equal - some
> are
> > much more robust in terms of thermal excursion degradation than others.
I
> > recommend you conduct a solderability test per JSTD-003 to determine if
> > your solderability has gone south or if you are having a solder process
> > issue. Good Luck.
> >
> > Dave
> >
> >
> >
> >
> > Yannick Brisson <[log in to unmask]>@ipc.org> on 11/25/2002 07:03:35 AM
> >
> > Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please
> respond
> >        to Yannick Brisson <[log in to unmask]>
> >
> > Sent by:    TechNet <[log in to unmask]>
> >
> >
> > To:    [log in to unmask]
> > cc:
> >
> > Subject:    [TN] Immersion Tin
> >
> >
> > Hi,
> >
> >   I made a board wich I plated with immersion Tin, I tought it should be
> > the
> > same result as we had with tin lead but we ran into a weird problem.  We
> > use
> > a 63/37  no clean paste and on the Board with Immersion Tin the solder
> just
> > make a ball ON the pad...we ran the same profile with a board Tin-Lead
> and
> > we get almost a perfect solder joint.  Because it's immersion tin should
> we
> > put our temperature higher?
> >
> >   We try to solder with a iron and the paste can hardly wet all the pad
> the
> > fisrt time..if we do it a first time, cleand the pad and do it again
it's
> > more easy.  If someone have work with it can give me some trick I would
> > appreciate.
> >
> > Thanks You
> >
> > Yannick Brisson
> > ============================
> > Technicien Ingénierie de Production
> > Technician Production ingineering
> > M2S Électronique
> > 2855, Rue de Celles
> > Québec, Québec
> > G2C 1K7
> > Téléphone: (418) 842-1312 Ext: 264
> > Télécopie: (418) 842-0123
> > [log in to unmask]
> > ============================
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