Perhaps I should have mentioned that the UK military issued a standard
test method in 1986 that did remove many of the ignored variables of the
US standard test method. If anyone is interested, I can look up the ref.
and put it on here. Incidentally, as a result of several years research,
led by Alan Stopes of the Aquila research centre in Bromley, Kent, the
same spec actually recommended the use of water-soluble fluxes, over
rosin-based ones, provided that the process was controlled according to
their test method.
Another point that should have been brought up is the fact that all
these specs were developed long before SMT saw the light of day. The
finest track/spacings in those days were ordinarily about 0.5 mm, 0.3 mm
being almost state-of-the-art. The components were better spaced than
today with larger stand-offs. Today's assemblies, especially HDIS, are a
whole new kettle of fish and to apply standards that are 35 years old to
them is just plain, plumb, crazy.
Still one more: how many people have tried to apply ionic contamination
testing to "no-clean" fluxes? This is even plainer, plumber, crazier,
without MANY qualifications. These tests were developed as a reasonably
easy process control for the quality of cleaning, not for determining
the nature of the residues on uncleaned assemblies.
My advice: forget blanket figures. Do as I say in my earlier post by
simple statistical process control on qualified and proven products.
Not to blow my own trumpet but simply as a statement for the younger
ones here who have never heard of me that my credentials involve much
research in this subject from 1975 to 1997 (when I "retired"), having
developed many instruments for this and other cleanliness testing
methods, including two of the most sophisticated ionic contamination
testers that have ever appeared on the market.
Brian
Macko, Joe @ IEC wrote:
> Fellow techs,
>
>
>
> Good morning.
>
> We have an Omegameter 600SMD that is used to check boards for ionic
> contaminates. The ionic residue limit within J-STD-001C, para. 8.3.6 is 10
> ug/sq. NaCl. Some personnel believe that this number should be adjusted
> based on the actual instrument used (e.g., an Omegameter). Would someone be
> so kind as to comment on this subject and what the correct limit is for an
> Omegameter type of instrument.
>
>
>
> Thanks
>
> joe
>
>
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