Thank you, Julie. Excellent post. 
My only comment is on number 4. Depending on the type of no-clean flux (liquid benchtop versus tacky no-clean that hardens after soldering), I agree that the tacky flux that hardens should not be cleaned. Liquid benchtop flux that does not harden, and leaves a sticky residue, should be cleaned and can be cleaned with a number of solvents, including water wash with a good saponifier.To answer Robert's question about an example of this, there are many. One example would be Kester 959, but they are very common.
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From: TechNet [[log in to unmask]] On Behalf Of Julie Silk [[log in to unmask]]
Sent: Thursday, April 26, 2012 5:33 PM
To: [log in to unmask]
Subject: Re: [TN] 4 Questions: No Clean vs flux Deactivation. Possible Hogwash ???

There is a language issue between active, activated, chemically active vs actively providing a solderable surface.  I'll answer in complete sentences to get to the gist of your questions
1.  Acid-based fluxes are chemically active when cold, the acid will etch, corrode, provide conductive paths.  The rosin in the flux is activated when it is heated.  When cooled, the rosin is no longer active for making solder joints, but the acid continues to be active for corroding and conducting.
2.  We want flux to be active during the soldering period.  It is not unaltered at the end of soldering.  Rosin, RMA and no-clean flux hardens upon cooling.  Acceptable flux residues are hard, not tacky and seal in the bulk of any remaining active acid ingredients.  The heating also changes certain acid ingredients into inactive compounds.  This is what Richard Stadem meant by deactivating the solder.  Liquid no-clean flux that has not been heated to soldering temperatures still has active conductive and corrosive compounds that will create reliability issues.
3.  The ionic contamination test is barely relevant, and in my opinion is a convenient shortcut to evaluating cleanliness that lost its usefulness with surface mount assembly.  The important test is surface insulation resistance.  A tiny bit of conductive flux residue under my high value resistor will kill my circuit performance and yet test just fine with ionic contamination testing.  There are many, many flux chemistries that will pass SIR and last for a long time in commercial applications.  I can't speak to space applications.
4.  No-clean fluxes are truly no-clean when used properly and should not be cleaned.  Cleaning no-clean flux will give you a dirtier surface than cleaning a flux designed for cleaning.  In an application that we had that required wire-bonding after soldering, no amount of cleaning process could eliminate the flux residues completely.  Switched to water-clean and our bonding problems went away.

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