Brian,
Was the ESTEC study you refer to ever published? If so, can you provide
the reference?
Doug Pauls
Brian Ellis <[log in to unmask]>
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Re: [TN] ROSE Equivalency Factors
I agree with Doug. The European Space Agency (ESTEC) did a profound
study with 4 different makes of tester and (I think) 6 different types
of flux, cleaned according to manufacturers' recommendations and found
there was absolutely zero correlation between them. It was impossible to
determine a so-called equivalency factor (aka as fiddle factor or fudge
factor) for any given instrument, as it varied greatly with different
fluxes and different cleaning processes. The whole notion was dreamt up
by NAFI in a nightmare; their testing was unscientific as they
determined it for instruments very different for those used today with
uncleaned boards, using a reference method that is, in itself,
unscientific and imprecise.
Forget the whole notion of equivalence because none exists and the
figures were, in any case, determined for instruments that were marketed
a quarter of a century ago and whose only resemblance to todays' ones is
that they may bear the same name. The ONLY way of using ionic
contamination testers is, during qualification, to determine the mean
and the standard deviation of the residual contamination on assemblies
deemed safe for the intended purpose, individually for each type of
board you make, using YOUR instrument under standardised conditions.
During manufacture, the mean should fit within the Gaussian curve
determined during qualification. If it deviates in either direction,
then you know that your process has changed somewhere along the line
between goods-in and cleaning.
If you have a certain book, Chapter 20 explains the danger of using
equivalence factors and the use of mean/standard deviation for
determining SAFE process control.
Brian
Richard Kraszewski wrote:
> Can someone please refresh my memory and tell me which document has the
> equivalency factors for the various ROSE testers? I seem to think that
> it was the IPC TR 583, but I don't see them there. Believe it may have
> been a Military document.
>
> Thanks
>
> Rich Kraszewski
>
>
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