What is the preferred surface finish for PWB's with PBGA packages?
     
     I have been looking at some published industry data regarding PWA 
     assemblies with plastic BGA's and so far all have had HASL surface 
     finish and very little data on OSP (organic Solderability 
     Preservatives such as Entek) coated boards.
     
     Has anyone had any OSP coated (Entek 106) mother board designs with 
     BGA packages in production?
     What are the pro and con's with HASL Vs. ENTEK for BGA assembly? 
     Using Entek boards, what kind of flux is better to use, NO CLEAN or 
     water soluble? 
     The preferred surface finish for assembling fine pitch components has 
     become Entek (or Entek equivalent) for better coplanarity criteria, 
     but is there a danger using Entek boards for BGA assembly? 
      
     I would greatly appreciate any information you can share with me.
     
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     Thanks, Gita