James

Father Doug has said it all. Whatever, forget your 2 megohm malarky,
which is utterly meaningless unless you go back to the original work by
Hobson et al. in 1969 and should never have got into a MIL Spec, in the
first place. Use a decent commercial ionic contamination tester -- there
are a number of models commercially available -- establish a baseline
result with it, using your old cleaning method (which, presumably, was
acceptable) and then use that as your criterion for the new method. It
is a starting point, albeit that the absolute value is more or less
meaningless. Then do your SIR/ECMR testing to qualify your process. If
everything passes with flying colours, you can then use your established
baseline values of ionic contamination as the criterion for continued
process control of the fluxing/soldering/cleaning process. Any
consistent variations in either direction with a single given PCB
assembly type means that something has gone out of kilter. Do NOT ignore
better-than-baseline results: they can mean that your process is way
out: the fact that ionic contamination is better for no apparent reason
MAY seem to be good news, but it could also be bad news.

Brian

"Marsico, James" wrote:
>
> Happy Monday, Technet:
>
> I'm trying to qualify a new cleaning process for electrical assemblies prior
> to conformal coating (Military boards).  The old MIL Specs had as
> cleanliness requirement of 2 meg-ohms minimum, is this all I need to do,
> verify cleanliness to 2 meg-ohms?  What about subjecting the assemblies to
> 10-day elevated temp/humidity (steady state)?  Any recommendations?
>
> Jim Marsico
> Senior Engineer
> Production Engineering
> EDO Electronics Systems Group
> [log in to unmask] <mailto:[log in to unmask]>
> 631-595-5879
>
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