Phil,
When you say that the white residue, which appears either as isolated spots
or globally, appears after final cleaning, it indicates to me that the
residue is either abietic acid, if you are using a high-solids rosin
flux/paste, or an interactive product between the weak organic acids and
water, if you are using a low solids flux.  If you are using a water soluble
flux, the white residue could be residual paste/flux, especially if you are
using tap water as a cleaning media.

Some questions to answer:
1.  What flux technology are you using?  A formulation reference would be
helpful.
2.  What cleaning solutions are you using?  Tap water?  DI?  Saponifier?
(Gasp)- CFC?
3.  Are you doing fine pitch work?  Surface Mount?  Through hole?

We often do residue analysis for customers who ask "What is this stuff?"
 Please give me a call and we can discuss it.  I can synopsize for TechNet
people later.

Doug Pauls
Contamination Studies Laboratories
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(317) 457-8095