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August 2002

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Subject:
From:
Graham Naisbitt <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 13 Aug 2002 16:02:32 +0100
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Bev and other interested parties,

IMHO, SEM and Ion Chromatography ought to be conducted AFTER any SIR testing
because:

SIR will inform you if the end product will be reliable, but won't inform
you why and what is on the surface causing the problem.

IC will inform you exactly what is on the surface, but won't easily inform
you if the product will be reliable.

As MoonMan and others have said, there is a quality product to deliver, and
probably via a no-clean process so that ROSE / SEC testing really wouldn't
be ideal. Added to which, it only measures ionics yet there are non-ionic
contaminants.

To give everyone a simple approach for production, then leave the
examination of the faulty and tricky stuff to the scientists - consider:

With the latest SIR approach, run tests using coupons that are run in series
with the final assembly - i.e. EXACTLY the same manufacturing processes. We
then test at 20 minute intervals over 3 days. In running the tests, we would
take samples of the coupons at each different wet chemistry stage of the
manufacturing process viz: Bare board - HASL (or whatever) - Flux - Adhesive
- Paste - Coating and so on.

Ah! But it's the interpretation of the results" I hear you say...?

W E L L ! Y e s... So what we are suggesting is to reject anything that
yields an SIR during test of less than 10^8 Log Ohm on the basis that it
will - A Be unreliable and B - Otherwise involve too much work to find out
why - although this does of course assume that you have some good results!

If the SIR results are good, then you almost certainly have an acceptable
production process...but for how long?

Well, I thought of that one as well, and you could continue to use the SIR
method to take appropriate samples at each assembly stage and with trend
analysis of the results, determine if anything has changed - e.g. the flux
stage gives totally different readings because there is a different operator
on the night shift or - and this could never happen - the vendor has changed
the formulation without notification.

Hope this helps


Regards, Graham Naisbitt
--
[log in to unmask]

Concoat - Engineering Reliability in Electronics
Concoat Systems - Measuring Electronics Reliability
Synergie - Electro-chemically compatible process chemistries

Concoat Limited
Alasan House, Albany Park
Camberley, GU16 7PH - UK

Phone: +44 (0)1276 691100
Fax: +44 (0)1276 691227
Mobile: +44 (0)79 6858 2121
Web: www.concoat.co.uk  &  www.concoatsystems.com


> Peter,
> I think Doug and probably Brian will answer most of your questions (with at
> least a few "it depends"), but I will chime in on a few.
>
> In-situ techniques are SEM/EDX and Fourier Transform Infrared Spectrometry
> (FTIR).  However, (oh don't we love THAT word)  the former will only give
> you elemental mapping, so you don't know whether the material is in ionic
> form or not. Conventional FTIR can ideally identify covalently bonded
> compounds.  Why so many modifiers in my sentence? Because if you have a
> large number of materials, like more than three, FTIR by itself cannot
> deconvolute the superimposed spectra to tell you what the individual
> compounds are.  Can a chemist make some guesses? Probably.  Also simple
> salts like sodium chloride or potassium bromide do not have pure covalent
> bonds and the lattice vibrations are so low in frequency that the optical
> material and materials in the atmosphere of your spectrometer will absorb
> all the radiation in the band width of these vibrations and you will never
> see them.  Also, both of these techniques are line-of-sight so if your
> residue of interest is under a component that you can't tear off the board,
> forget it.
>
> Some companies have also perfected techniques for building little dams on
> printed circuit packs to puddle solvents for local extractions for ion
> chromatography, but this is time consuming and very expensive as a result.
>
> Looking forward to other replies.
>
> regards,
> Bev Christian
> Research in Motion
>

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