Good Morning everyone,
Doug, Graham is not more restrained than you - I've been out for a couple of
days visiting customers! However, burning the heretic Brian, is perhaps a
little strong - even for you. Always bear in mind that Brian is a British
exile first (to my knowledge) to Switzerland now to Cyprus. SIRBrian has to
keep moving because that makes him a more difficult target to hit!!
Scott, sorry I had to get that bit out of the way first.
You state:
> I have been observing this thread with interest. We run standard SIR
> coupons monthly through our production floor to monitor our cleaning
> processes (SMT, wave, DI wash, water-soluble flux chemistry, standard
> production processes and handling).
Can you please inform me the method you use, the type of coupon and is the
test pattern overmounted with components?
Are you running this test using coupons from each process stage or simply on
"completed" coupons?
>
> My question: Is all of this necessary? Would it be possible to gauge
> acceptable cleanliness levels based on another type of measurement, such
as
> Ion chromatography? Or does IC miss things that SIR picks up?
Is it necessary? Well what is the level of deviation you have seen from your
SIR results?
IC will inform you EXACTLY what is on the surface - but, unless you are Doug
it cannot inform you if the product is reliable.
SIR will inform you if the product is reliable, it cannot inform you what is
on the surface that may be causing a reliability problem.
>
> It's plausible that localized contamination, say underneath a low profile
> QFP, might not raise the overall contamination levels much, but would have
a
> detrimental localized affect.
Agreed. As I always point out, the industry desire to use a simple pass /
fail ROSE level of <1.5microgrammes/square centimeter NaCl equivalence (in
line with another current TechNet thread that Joyce posed) also implies that
it is acceptable to leave UP TO that level on every square centimeter of
your assembly. If you manufacture fine-line fine-pitch and / or use CSP
devices, then this level will almost certainly prove to be too high. As an
example, I know that certain sections of IBM employ a level < 0.2.
In respect to Brian's suggestion to "start with a clean slate", I cannot see
why, unless you have discovered a new application for Retsina? The NPL
carried out an extesive research project some years ago, into different
methods of defining "clean, reliable" (my interpretation) electronic
assemblies. They listed some 22 different methods most of which are
destructive.
The 2 best were considered IC and SIR. There was also a consideration for
Impedence Spectroscopy, but that hasn't materialised yet.
As I have just stated, there is an application for both methods to be used.
SIR to inform you the level of reliability by its measuring the degree of
current leakage from REPRESENTATIVE coupons processed in parallel with your
production. This at least seem to be what Scott is doing at Benchmark.
Then if a problem is discovered, IC would be useful in determining the EXACT
nature of the dendritic failure.
And if my Latin isn't too rusty - Brian suggests he is "I am (either) a
develish (or) diabilical advocate (lawyer or attorney) who is in the dog
house!?"
As I said in my old latin school book from dumpty-dum years ago: Latin is a
language as dead as dead can be, it killed the ancient romans and now its
killing me".
I look forward to Scotts reply - and no doubt Brian and Dougs!!
Regards,
Graham Naisbitt
[log in to unmask]
WEB: http://www.concoat.co.uk
CONCOAT Ltd
Alasan House, Albany Park
CAMBERLEY GU15 2PL UK
Tel: +44 (0) 1276 691100 Fax: +44 (0) 1276 691227
> -----Original Message-----
> From: Brian Ellis [mailto:[log in to unmask]]
> Sent: Thursday, February 24, 2000 10:36 AM
> To: [log in to unmask]
> Subject: Re: [TN] AW: [TN] components cleanliness
>
>
> Doug
>
> I thought that one would get you to rise to the bait :-) Am surprised
Graham
> hasn't reacted, either.
>
> Seriously, I consider this an important problem as very few assemblers
test
> the
> bare boards they receive, let alone the components. I consider that there
> are
> also many other ignored parameters, some of which I brought up during
> various
> IPC and ISO WG meetings, to be shot down - for the most part - in flames.
>
> Unfortunately, I do not have an answer to all these problems. I'm a great
> one
> for actually putting the test patterns on the real PCBs, as close to
> critical
> components as possible, but even that is less-than-ideal :-(
>
> If the truth be told, I honestly believe that we should forget all we have
> in
> the way of ECMR and SIR standards and start again with a totally clean
> slate,
> beginning with the basic definitions which have become so distorted as to
be
> misleading. There are FAR too many legacies from test methods and
standards
> that
> date from 30, 40 or more years. Not only did we not have an understanding
of
> what it was all about, then, we didn't have sufficiently good instruments
> and
> even most of those available today leave a lot to be desired. I have never
> seen
> an in-depth scientific analysis of all the mechanisms that can influence
the
> results. From time-to-time, I've brought up some practical observations,
> over
> the past 20 years, some of which have created discussion and others,
> yourself
> likewise, have done the same. Furthermore, we need to address present
> issues,
> let alone future ones. Who, e.g., has done anything about SIR on HDISs
with
> track spacings down to 25 um?
>
> Advocatus diaboli sum (and probably in dome canis est, by your lights!).
>
> Best regards
>
> Brian
>
>
>
> [log in to unmask] wrote:
>
> > In a message dated 02/23/2000 3:09:10 AM US Eastern Standard Time,
> > [log in to unmask] writes:
> >
> > >
> > > This is the main reason why SIR testing is, in many cases, useless to
> > > qualify a flux: you qualify it under lab conditions, totally ignoring
> > > the fact that its behavious will alter in practice due to it mixing
> with
> > > external contaminants not present on your test vehicles.
> > >
> >
> > SIR USELESS? Gasp!! Burn the Heretic!!!!!!!!!!
> >
> > SIR can be useful, even as a lab tool, you just have to use the right
> > combination of materials, processes, environment and data
interpretation.
> I
> > would agree that we have a long way to go before our existing methods
are
> a
> > good and true measure of field performance.
> >
> > Doug Pauls
>
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