> 
>      I have a question concerning repair of a CCAs soldered with 
>      no-clean flux (hand soldered and/or wave soldered).  

What's a CCA?
>      
>      If you need to repair/rework the CCA, do you use an RMA flux 
>      for the repair/rework or no-clean flux? If you use a 
>      no-clean flux, how do you know if you have flashed off all 
>      the flux that was applied?  Wave soldering pretty much 
>      covers the entire bottom side flashing off the no-clean 
>      flux, however, a soldering iron may not do that.   

Certain RMA fluxes, such as Alpha 615-15,
can be left on boards with good results if:

* One isn't pin testing after rework.

* DC or low frequency. No high speed digital or high frequency.
  Over 1 Mhz is a high frequency.

* The flux residue is not left on a switch contact.  This can cause
  bad contact resistances.

* A bit of slightly unattractive yellow residue is ok.
  These RMA residues should not cause any corrosion or
  current leakage problems.

If you are using a RMA for reworking no-clean assembly,
lighter is better.  Use 10 to 15% flux solids.
Also use a RMA core solder, like Reliacore 15.

Certain low residue fluxes are better for rework than others.
Alpha NR205 is better than Alpha NR200.  Ask your flux supplier
for advice.  Other flux and solder manufacturers also sell
appropriate products (and inappropriate products) for these 
applications.  The residues from a low residue, organic acid 
no-clean flux may indeed be left behind by a hand soldering.
A hot air gun or baking for 20 minutes in a 100C oven should
volatilize most organic acid residues.  Some organic acid residues
can be removed by water, most can be removed by isopropanol.
>      
>      If you use an RMA and clean then it would seem you are 
>      defeating the purpose of the no-clean.  Will that cause a 
>      problem since the rest of the CCA was soldered using 
>      no-clean?
>      
>      I have heard of cleanable no-cleans, but, what if you are 
>      not using a cleanable no-clean.  Could someone straighten me 
>      out on this issue?  Thanks!
> 

I hope this helps, if you have further questions, send me email.

-- 
Karen Tellefsen
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