Julie,
I completely agree with everything you stated. 
I wanted to clarify that the isolated spot cleaning is only intended to be used on conformally-coated boards that cannot undergo in-line or other automated cleaning, whether available or not. 
If documented properly, it is very repeatable. 
We use a proprietary method to flush and remove de-ionized water in the rework area, then bake dry.
We qualified the process by using ion chromatography on several samples, including worst-case situations where different flux types were burnt and baked on, they all passed the testing.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Tuesday, April 24, 2012 3:47 PM
To: [log in to unmask]
Subject: Re: [TN] No-Clean Flux

Julie,

 Not allowing rework folks to could lead to rework quality issues.

 The only solution (pun intended) was a full wash after rework. Using a WS reflow flux followed by any through hole and rework before the 1st clean is what we did. Problem was it is after the was that 1st wash when additional rework might be required. If so then we did a second wash cycle.

Bob K.

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Julie Silk
Sent: Tuesday, April 24, 2012 3:37 PM
To: [log in to unmask]
Subject: Re: [TN] No-Clean Flux

I agree with the majority of the group that no-clean liquid flux that has not been deactivated is a reliability issue.  It remains conductive, and is tacky enough to collect debris and dust to make an additional conductive path.  It's a poor practice to use liquid flux for hand-rework, and yet seems prevalent.  

Since I intensely dislike spot-cleaning operations (too variable, operator-dependent, spreads gunk in a broader area and under parts), I prefer to ban liquid flux use in rework in settings where an automated cleaning process is not available.  Even a single drop applicator gives enough flux to spread into regions that will not be heated by a soldering iron.  I have never seen an operator wait a couple of minutes after fluxing before going in to solder, either.  The flux pen is the best bet, and yet I've seen it swiped liberally all over the region to be soldered and not just the local area.  

I think the IPC 610 10.6.4 standard that was referenced is inadequate (one of the few places where Agilent disagrees with IPC and our internal standards are tighter).  It sounds like wet, tacky or excessive flux residues are only a defect when they may spread onto other surfaces.  Wet and tacky residues -- or ones that were tacky enough to exhibit fingerprints (!) -- are unacceptable.  Period.


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