For the general precision defluxing of hybrid circuits, nothing can beat the Lead-Free Flux Remover - PowerClean™ (#MCC-PW2). This is a powerful cleaner, functionally equivalent to the old Freon® TMC or Genesolv® 2004. PowerClean™ dries fast, offers powerful cleaning on most fluxes, it's nonflammable, it has a very low aroma, and is easy to use and to store. It's a great choice.
A newer choice, but slightly milder, is the VOC- Free Flux Remover - UltraClean™. This is a medium-strength cleaner that is engineered for communities with the tightest restrictions on using VOCs.
An older answer is the General Purpose Degreaser (#MCC-AXL). Originally developed by DuPont for cleaning hybrids, this is a hydrocarbon solvent that it is derived from petroleum products. Plastic-safe and slow drying, it has a modest aroma and delivers moderately powerful cleaning. It represents a very good combination of characteristics.