Armand
How long is a piece of string? I know guys who clean successfully with plain untreated
tap water at 200 µs-cm and some who don't using 1 µS-cm DI water. (I'll talk
conductivity as being more intuitive than resistivity, being linear: if you wish to
convert resistivity (Mohms-cm) = 1/conductivity (µS-cm)). The difference? a) the nature
of the residues b) the nature of the substrate, c) the effectiveness of the cleaning
machine and d) whether drying is done mechanically or by evaporation (non-exhaustive
list, probably a score more could be added).
To the best of my knowledge, there are no standards, nor can I see how there could be a
scientifically established standard, as there are too many uncontrolled parameters.
As a rule of thumb, if you use a good w/s chemistry, if you have a good and effective
machine with at least 3 or 4 rinses, of a type able to get the stuff out from under the
components, and if you use mechanical drying (air knife or centrifugal), then you
should generally have little trouble if you regenerate your resin beds when the water
rises to 10 µS-cm. Under these conditions your ionic contamination should be under
about 0,3 µg/cm2 eq. NaCl, which is quite good (the figure will vary according to a
number of factors, which I have not specified, but you should have little problem even
if it is as high as 1 µg/cm2 eq. NaCl except for some niche applications).
Brian
Armand Nitro wrote:
> TechNetters,
> I would like to know if there's any existing standard or article that
> indicates or calls-out that the minimum
> resistivity for DI water used in aqueous cleaning is 0.1Meg-Ohm (This is
> what I know for other types of electronic asssemblies). Is this applicable
> to all types of electronic assemblies ? In our operations, we are currently
> using 0.2 as minimum resistivity and I am planning to lower it down to 0.1
> but before I proceed in performing the experiment/evaluation, I need to
> understand and know what is being called-out as a standard.
> What are the other type of test/s that could be performed aside from Ionic
> Contamination Test
> in order to prove out that 0.1 DI water really have that cleaning capability
> ?
>
> Thanks...
> Armand Nitro
>
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