It is impossible to give a cut-and-dried answer as there are far too
many variables. Personally, I am STRONGLY opposed to using rinse water
conductivity/resistivity as a measure of cleanliness because:
a) the water does not know what components and materials you are using
and their spacing
b) nor does it know how efficient your machine is at cleaning and
rinsing, how many nozzles are blocked or spraying badly etc.
c) nor does it know whether your drying will be largely mechanical
(good) or largely evaporative (bad)
d) nor does it know the conditions of use of the end product
e) etc.

In other words, you cannot use such a parameter as a process quality
control. It is not meant for that; it is meant to tell you when the DI
columns need regenerating, nothing more nor less. In order to determine
all the parameters of a cleaning system, there is only one way, a full
series of qualification tests, which includes SIR and ionics (possibly
chromatography), according to your individual requirements of
reliability of the finished product etc., followed by daily process
controls, of which monitoring the resistivity of your final rinse water
will be only a minor part. You may find that you may need to go up to 10
megohm-cm or that you can go down to 0.05 megohm-cm. I've seen both
these figures in many decades of cleaning experience as the first
aqueous cleaning machine manufacturer in Europe and a contamination and
SIR tester manufacturer. Believe me!

Brian

Macko, Joe @ IEC wrote:
> Hi,
>
>
>
> We are evaluating the cleaning ability of a new batch cleaner, which has the
> ability to monitor the resistivity of the actual DI rinse water throughout
> the rinse cycle.  I checked the archives as well as other sources and it
> seems like the consensus ranges from 100K to 750K ohms with most suggesting
> 500K ohm as a good, acceptable resistivity level.  I am trying to establish
> a basis for what is an acceptable final rinse resistivity level for the
> boards we process.  We use RMA based flux.  We also have an incoming DI
> rinse water resistivity meter for reference.
>
>
>
> Would anyone be so kind as to point me in the right direction?  Thanks in
> advance.
>
>
>
> Joe
>
>
>
>
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