Brian, Doug, All.

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).

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?

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.

Any comments are welcome, I don't even consider myself a rookie in this
portion of our field.

Scott Severson
Benchmark Electronics Inc - Winona Division
-----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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