Steve

Just a few thoughts before the gurus speak. If you do an extraction 
conductivity test, as you suggest, what will you be measuring after 
soldering? The residues from your no-clean flux, not the cleanliness of 
your assembly. Are these important? Possibly, but...

What may be important (depending mainly on your board manufacturer) is 
whether the boards are clean before fluxing/soldering/reflow. IMHO, this 
is the most important thing to test.

Personally, for a 'no-clean' process I would not test for ionic 
contamination after soldering. Instead, I would rely on a reputable 
well-chosen flux and let it go at that. This does not mean you can use 
out-dated or contaminated flux/paste or that your housekeeping leaves to 
be desired.  You will still need good, ordinary, practices.

FWIW

Brian

On 23/06/2017 14:50, Steve wrote:
> I realize that this is an old and continuing subject of debate in the industry, but I am interested in the current updated consensus on the topic. Specifically, what kind of PCBA cleanliness level should be reasonably expected to achieve?
>
> Of course the answer is always "it depends," because that is the reality. And the actual acceptance or control level needs to be set according to product requirements. But what I am after is slightly different: What level of cleanliness would you expect to be readily achieved by a good quality manufacturing process under normal circumstances?
>
> Some general parameters to narrow down the question:
>
> - Measurement technique bulk solvent (ROSE per IPC TM-650 2.2.25)
> - Pretty normal PCBA design - 0403 components, some through hole, nothing really unusual
> - Pretty normal process, RoHS, no-clean.
> - Class 2 PCBA, but high impedance low current battery powered application
> - High production volume (>1 million units annually)
>
> I am not aware of anything that has replaced the 1.56/cm^2 "standard." but this has been around forever, it seems. Common sense tells me that even if a formal standard has not changed general performance might have improved, on account of smaller components, tighter board spacing and general technological improvements.
>
> What has been your actual experience in this regard?
>
> Thanks in advance,
> Steve
>