I've always considered 1 megohm-cm or 1 µS-cm as somewhere about the
limit, but this can depend on a number of factors. For example, if the
excess water is blown off by high-power air-knives, then one can usually
tolerate a poorer quality water. One of my customers insisted on 0.1
µS-cm (10 megohm-cm) but I think he was over the top.

Of course, the real answer is the quality of water which allows you to
produce assemblies with the reliability you are seeking. As I remember
when I visited your factory, you were using a self-surfacting solvent +
water wash for flux removal in a cleaning machine of UK origin with QC
using a low-cost ionic contamination tester. I believe drying in that
equipment may have been problematic, so that a good quality water would
be necessary, because any residual contaminants on the board would be
simply dried on around the connection areas. (Of course, you may have
changed something in the meanwhile.) However, your tester should give
you a reasonable clue as to whether your process is OK. For your kind of
production and process, I would suggest that if you are getting better
than 0.5 µg/cm2 eq. NaCl, you are probably on the right lines.

Brian

Sedat BAYAR wrote:
> Dear Technetters,
>
> What is the minimum acceptable DI water resistivity value for the final rinse operation at the in-line CCA cleaning system?
>
> Regards,
>
> Sedat BAYAR
> Aselsan Inc.
>
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