I also agree, but guess what? That is true of any CCA, no matter which flux chemistry (NC, RMA, WS) or type (solder paste, liquid flux, tacky flux) is used.
The ROSE test results are much more constant when attempting to measure cleanliness of CCAs processed with water-soluble fluxes, where 99.9% of the flux residues are washed off. The ROSE test results jump all over the place when attempting to measure ionic cleanliness of CCAs processed with no-clean residues, not quite so bad for RMA. So unless a wash process can clean NC or RMA fluxes really, really well, the ROSE test data is somewhat less useful.

The amounts of flux residues seen after cleaning varies much more with NC and RMA not only because they are more difficult to clean, but also because they are more time-variable than water-soluble flux residues. Just solder up two identical lots of SMT-only CCAs with RMA or NC paste only (no benchtop or tacky flux added). Run one lot through the wash immediately after soldering side 1 and again after soldering side 2, and run the other through the wash after soldering both side one and side two and then waiting one hour. I guarantee the second lot will have much higher ugrams/cm of NaCl equivalency than the first. Do the same with two lots of water-soluble, and little or no difference is seen later at the ionograph. 

It also depends on which brand of NC or RMA is used also. Some are much, much worse than others when it comes time to clean.

And cleanability does not always correlate with activity level, ie, fluxes with higher activity levels which result in better soldering may or may not be easier/harder to clean.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Karen Tellefsen
Sent: Tuesday, July 10, 2012 10:52 AM
To: [log in to unmask]
Subject: Re: [TN] Ionic Contamination Test for Non-clean PCBA, is it really necessary?

I agree, and Jack Brous's white paper tells just about the same thing. 
It's only good for statistical process control.

Karen Tellefsen - Electrical Testing
Alpha / 109 Corporate Blvd./ S. Plainfield, NJ 07080 [log in to unmask]
908-791-3069




From:   Brian Ellis <[log in to unmask]>
To:     <[log in to unmask]>, 
Date:   07/10/2012 11:05 AM
Subject:        Re: [TN] Ionic Contamination Test for Non-clean PCBA, is 
it really necessary?
Sent by:        TechNet <[log in to unmask]>



I'm one of Kevin's "have written a book"! Ionic contamination testing on "no-clean" assemblies is totally meaningless unless conducted under very rigorous conditions for the unique purpose of statistical process control. This may tell you something about whether your process is constant or not. It will tell you absolutely nothing about the quality or reliability of your products.

Brian

On 10/07/2012 09:13, WTSJ-Willis Tam wrote:
> Hi Technet,
>
> We have implemented non-clean SMT and wave soldering processes for 
> more
than
> 10 years and there's no any issue, but recently one of our new 
> customer required us to buy the Omega tester and set up the Ionic 
> Contamination
test
> for the non-clean PCBA, according to IPC-TM-650. 2.3.25.
>
> We feel the Ionic Contamination test might not be an appropriate test
for the
> non-clean PCBA, but is there any technical paper or industry standard
for
> this topic? We need some supporting documents for further discussion
with our
> customer.
>
> Any suggestion/feedback would be appreciated.
>
> Regards
> Willis Tam
>
>
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