Gaby
There is no reason to suspect that soldering issues of any kind will be
aggravated by immersion silver provided the chemistry is up to par, the
process is within the bath supplier's spec and there is an adequate quality
control process in place. Immersion silver has been widely used by many OEMs
with great success, AT&T, Andrew etc. Immersion sliver voids have been
reported by some suppliers, but most of these issues were resolved by the
MacDermid study, I imagine Danny Fritz can get you a copy of the paper. I
installed this process in the AT&T Richmond Works in 95. I have not heard of
any soldering issues that were not quickly resolved, certainly nothing on
the order of black pad.
I would certainly qualify any potential supplier to verify the process meets
the vendor's spec and that a quality control plan is in place and on going.
I would also monitor the quality of the silver coating (thickness
measurements, cross sections and solderability assessments etc.) If the
quality of the coating is robust over a extended period of time, I would
then begin to expand the inspection interval.
To insure a quality product from all stand points it is absolutely necessary
to continuously monitor the supplier with on site visits whether the
supplier is on shore or off shore. This of course is one of the
disadvantages of off shore suppliers.
Best regards
Lee
J. Lee Parker, Ph.D.
JLP Consultants LLC
804 779 3389
----- Original Message -----
From: "Gabriela Bogdan" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, January 28, 2008 1:30 PM
Subject: Re: [TN] Microvoids immersion silver
> Thank you all for your information.
> Now, next:
> Opens in BGA on Immersion silver.
> MICROvoids detected by X-ray on : free pads, ordinary smt joints, BGA
> solder
> joints (ball to circuit pad location).
> BGA rework?
> BGA replacement?
> SCRAP??????
> I fear that the story begins to be similar to the black pad nightmare with
> immersion gold.....
> Gaby
> ----- Original Message -----
> From: "Dennis Fritz" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Monday, January 28, 2008 8:17 PM
> Subject: Re: [TN] Microvoids immersion silver
>
>
> >I will try to answer each question as you ask them.
> >
> > In a message dated 1/28/2008 12:32:15 P.M. Eastern Standard Time,
> > [log in to unmask] writes:
> >
> > Dear Netters,
> > Is there a preferred process for immersion silver finish in order to
> > minimize microvoids?
> > Immersion silver vendors have a preferred way for fabricators to operate
> > the
> > immersion silver line to minimize/prevent microvoids. Please
> > understand
> > there are more effects than just the immersion silver bath itself.
> >
> >
> > How do you choose the preferred immersion silver PCB supplier?
> > Your board supplier is very interactive in the performance of immersion
> > silver boards. The best plating solution, run poorly by a fabricator
> > can
> > give
> > problems and vice versa. Obtain boards from more than one fabricator
> > and
> > from
> > various bath suppliers. Probably, the bath vendor has an opinion, from
> > process audits, how each fabricator is obeying the process information
> > in
> > the data
> > sheets. See what works best with your solder paste and wave solder.
> > Wetting balance, dip-and-look, solder spread are all tests that
> > indicate
> > good
> > performance.
> >
> >
> > Which test for bare boards could give the best information?
> > IPC J-standard 003 for board solderability should be a guide for your
> > operation. Do you use international IEC standards?
> >
> >
> > Should I perform a print and reflow test for each batch, followed by
> > x-ray?
> > The print/reflow test is a good idea, with controlled conditions.
> > However,
> > I
> > don't think you will see microvoids with X-ray. You probably need cross
> > sectioning to see microvoids.
> >
> >
> > Which tests are the suppliers performing?
> > By suppliers, do you mean board fabricators or plating chemistry
> > suppliers?
> > This is not a one stop shop. The board shop should be running process
> > controls on their microetch for roughness and silver immersion plating
> > bath. The
> > plating rate and final thickness are recommended by the bath supplier,
> > and
> > should be obeyed in fabrication. Both shop and supplier may be running
> > assembly
> > simulation and then cross sectioning to see if there are any
> > microvoids.
> >
> >
> > Thanks,
> > Gaby
> >
> > Dennis Fritz
> > MacDermid, Inc.
> >
> >
> >
> > **************Start the year off right. Easy ways to stay in shape.
> > http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489
> >
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