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Subject:
From:
Joe Russeau <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Joe Russeau <[log in to unmask]>
Date:
Wed, 16 Apr 2008 09:43:11 -0400
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Agreed.  By-the-way, I like blunt,  it saves time.  One thing that I have 
yet to see mentioned, which complicates this issue more, is that the ROSE 
test uses a solution of 75% isopropanol and 25% deionized water.  The 
possible variations in flux formulations are enormous.  With all of this in 
mind, not all materials will dissolve in 75/25, nor do all materials 
dissolve at the same rate.  I would think this would be especially true for 
lead-free materials, given the fact that their residues tend to be more 
difficult to remove.  Therefore, I ask, how can a value that was developed 
over 30 years ago, for the higher rosin based fluxes, still apply to today? 
It absolutely makes no sense to think that it does.  Yet, somehow, that 
value keeps finding its way back into the standards.  Personally, I would 
like to see the ROSE test go the way of the dodo.  Although, I know that 
won't happen anytime soon.

Best Regards,

Joe Russeau



----- Original Message ----- 
From: "Brian Ellis" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, April 16, 2008 4:12 AM
Subject: Re: [TN] SV: [TN] Ionic Contamination Question


They may not have been set arbitrarily, but the reference test method as
per Hobson et al. 1969, in the Naval Avionics Facility, Indianapolis,
published 1972 as the first text adopted in standards was more than
arbitrary. It was probably the most unscientific piece of junk ever
perpetrated on industry. You could get it to read whatever you wanted it
to read, with a possible fiddle/fudge factor within limits of -100% to
+500%. In 1969, most of the electronics was on single-sided boards with
components whose size was larger than many of today's assemblies.
Typical minimal line widths and spacings were 1 mm each, if not larger.

IOW, that 39-y.o. reference method has absolutely no relevance in
today's electronics, and nor has Navy report MRR-3-78, which was based
on it 30 years ago. Mil-P-28809 (1975) and MIL-P-28809A (1981) -- the
latter permitting commercial instruments with totally artificial fudge
factors -- were the standards behind the 10 µg/in² eq. NaCl or 1.56/1.5
µg/cm² eq. NaCl but were hardly worth the paper they were printed on, as
far as ionic contamination was  concerned.

As has been mentioned on this forum many times, the only way of validly
using ionic contamination levels in modern electronics is:
1. qualify a flux/soldering method
2. qualify a cleaning method
3. determine if the reliability of the finished article is sufficient,
using SIR, ECMR, vesication etc. testing and possibly field life testing
4. do ionic contamination testing in the instrument of your choice of,
say, 20 samples of each and every assembly and determine the mean and
standard deviation.
5. do production run testing several times/day in the same instrument
with statistical analyses of the results. If they fit in the histogram
of the qualification testing statistics, then you know your process is
running correctly and you may sleep at night on both ears.

All the above was written in essence on pp 249-257 in a well-known book
which was published 22 years ago. AFAIK, no one has ever refuted this
commentary and analysis of the many weaknesses of the reference method
nor the need to rely on statistical analyses, rather than spot results,
which I advocated since 1979, just one year after the cited Navy Report.
In fact, I think it was published in the "Handbook of Contamination"
(1980): long since out of print.

The 1986 UK Def.Stan 00-10/3 took many of these factors (but not all)
into account and was, overall, the first ionic contamination test
standard that was based on more or less scientific principles and it set
a general limit value of 1.5 µg/cm² eq. NaCl, based on 4 years research
done at HMS Aquila, in Bromley, Kent. But remember that this was before
surface mounting became current and, in those days, the average PCB was
2 sided PTH with through-hole components and average track
widths/spacings of about 0.6 mm, 0.3 mm being hi-tech state of the art,
with relatively low yields. In fact, on p. 260 ibid., the notion of
different values for different types of assemblies was raised, with 1.0
µg/cm² eq. NaCl for surface mounting and 0.5 µg/cm² eq. NaCl for
critical assemblies, and this was over 22 years ago.

I maintain that anyone who blindly follows a limit of 1.5 µg/cm² eq.
NaCl or any other fixed value for spot checks, based on 39-year old
methods, at the best doubtful, needs to retire from industry before he
causes his employers the risk of untold harm.

Sorry for  being blunt! :-)

Brian

[log in to unmask] wrote:
> The levels were not set arbitrarily. They were set on basis of ionic 
> residues causing vesiccation & subsequent failure of military assemblies 
> in  high humidity environments (Vietnam). Specifically, ionic residues 
> from RMA  fluxes on conformally coated assemblies- most often radios. (See 
> Navy report  MRR-3-72). Mechanization of the original manual ionic testing 
> method led to the  different nbrs used for the various automated test 
> instruments, as published in  Navy report MRR-3-78. I wrote a column for 
> SMT magazine on this  issue; if you'd like a copy of the column, email me 
> separately at [log in to unmask] (mailto:[log in to unmask])  as it would 
> be stripped  off if I tried to email it to TechNet as an attachment.
> Bill  Kenyon
> Global Centre Consulting
> 3336 Birmingham Drive
> Fort Collins, CO  80526
> Tel: 970.207.9586   Cell:  970.980.6373
>
>
>
>
> **************It's Tax Time! Get tips, forms and advice on AOL Money & 
> Finance.      (http://money.aol.com/tax?NCID=aolcmp00300000002850)
>
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