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