John,
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.
These oxides (salts) will dissolve slowly during the SIR test, raising the
conductivity and thereby be measured as ionic contamination. 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.
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.
The cleaning solution should contain an anti-tarnishing agent that will
 inhibit any subsequent oxide formation. A good cleaner will remove oxides
(white haze) from the laminate as well as the fused solder. Products to
perform these functions do exist. Please contact me if you have any further
questions or comments.

Best regards,

Cormac Kissane
Technical Service Representative
RD Chemical Company
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