Cormac,
I have a few issues (friendly) with your response.

> The ionic contamination  the customer is measuring, is not actually being
>  "picked up" during shipping/handling, but rather, is likely the result of
>  oxides of Tin and/or Lead forming on the solder areas of the board.

>From the original description of the problem, I think the "contamination"
discussed is far more likely to be absorbed flux or fusing fluid from
fabrication than a metal oxide.  Metal oxides, unless they flake off
profusely, seldom affect a ROSE or SEC test to the magnitudes that flux or
solder mask residues do.

>  These oxides (salts) will dissolve slowly during the SIR test, raising the
>  conductivity and thereby be measured as ionic contamination. 

I think you meant to say SEC or ROSE test.  SIR testing in this particular
case would be a different ball game.

>  Is  the
>  customer's contamination limit practical?. Well, if one goes by the motto
>  that "the customer is always right", then the issue becomes what to do
about
>  the contamination.

No, the customer is not always right.  The customer often needs education to
understand the limitations of residue measurements and to explore more
suitable alternatives.  I've lost track of the number of conversations that I
have had convincing a customer that their "scientifically derived criteria"
are no better than a dart board and a blindfold.

>  Thorough  cleaning of the boards to reduce ionic contamination to
virtually
>  zero is essential and not have a situation where those boards that 
> marginally pass the ionagraph test after washing, go on to fail at customer
>  inspection.

This is just another case where you have to understand not just that a
residue is present, but what that residue is and if that residue is harmful.
 ROSE testers cannot do this.  Period.

>  The cleaning solution should contain an anti-tarnishing agent that will
>   inhibit any subsequent oxide formation. 

I don't know that I would agree with this.  Anti-tarnish agents could also be
ionically conductive when removed into solution.  A residual anti-tarnish
agent could as easily fail the end-item requirements here as help it.  In my
view, a good cleaner should remove the soils of interest and then be totally
removed.  

>  A good cleaner will remove oxides
>  (white haze) from the laminate as well as the fused solder. 

If you have a cleaning agent that will attack fused solder, you have an agent
that is too high in pH.  I have seen some saponifiers that turn solder joints
black or at least dull them significantly.  When this happens, there are all
kinds of bad effects that can happen.  In my view, a good cleaner might
brighten the solder joints a little, but it is not the job of a saponifier to
effect oxide removal.

Doug Pauls
CSL

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