Larry,

Check out the article "OSP's and the Assembly Process" found in the August
edition of Circuits Assembly Magazine.  The article not only points out
some of the main benefits(namely a flatter surface to screen print onto-
which leads to more controlled solder volumes), it also points out most of the
disadvantages(that include the degradation of the OSP coating during thermal
cycling and exposure to chemicals like proponol-which means the PCB handling
process may need to be tightened up, especially for class 2C assemblies).

We have changed over to OSP(organic solder preservatives) on many of the 
products we assemble, and have had great success overall; especially with
fine pitch assemblies.  
We had been warned by the OSP manufacturers about possible problems due to 
handling inflicted contamination, and coating degradation, but were happy to
discover the warnings were perhaps over cautious, as we have had no real
solderability problems with OPS's in the last 36 months.
                                                           Steve A

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