I'd like to add that it is essential that you evaluate your solder pastes as
well. There is a big difference among the many manufactured, not only in flux
performance but also in the flux's tendency to be efficiently cleaned.
A few months ago, while performing a very thorough solder paste analysis of
OA fluxes with a client, we found that even after subjecting boards soldered
with the candidate pastes to cleaning following the recommendations of their
respective manufactureres, we found that some left a residue under large
passives (i.e: tantalums) while some did not.  This we discovered by
subjecting the assemblies to spinning in a heated centrifuge.  (regards to
the gang at Textron !).
I discussed this finding with Terry Munson, "Mr. Clean" and he has observed
this as well. Thus as not all solder paste chemistries are equal,
particularly in this important facet, you must perform a thorough solder
paste evaluation.

Phil Zarrow
ITM, Inc,
Durham, NH
www: ITM-SMT.com