In broad terms: Rosin resin fluxes are not water soluble and can generally be left uncleaned. Organic acid fluxes are usually and inorganic always, removed as they are water soluble. (I say usually for organic acids as some very low residue wave soldering fluxes based on organic acids are classified no clean. Generally if a flux is classified OA it is to be cleaned). . Rosin is a particular type of natural resin, derived from pine trees. Resin is a generic term for a family of chemicals which includes synthetic and natural types. The first fluxes were made from rosin; later formulations used a mix of natural and synthetic resins. I Resin (rosin) fluxes can generally be left on the work after soldering - provided they meet specification such as those from IPC. References to rosin or rosin in flux specifications are really just for information as some legacy products, usually military, specify rosin based materials. Organic acid fluxes are nearly always removed after soldering by washing in water, with or without some added chemical. Inorganic acid fluxes are very much more active than organic acids and are not used in PCB assembly. Organic acid fluxes can be as (in) active as resins and approach the activity of inorganic acid fluxes. OSP is a standard PCB finish and therefore intended to be soldered using standard electronic fluxes including resin (rosin) materials. A minor caveat: It is sometimes difficult to solder OSP if storage times have been exceeded and/or on second side soldering as the OSP is intended to be dissipated by the heat of soldering. Hope this helps, If you search in the TechNet Archive you will find a lot more on this topic. Regards Mike Fenner Bonding Services & Products M: +44 [0] 7810 526 317 T: +44 [0] 1865 522 663 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of DATACOM - Juliano Ribeiro Sent: Thursday, August 15, 2013 6:07 PM To: [log in to unmask] Subject: [TN] Flux Type Hi to all, What are basically the differences between flux ROSIN X RESIN X ORGANIC and INORGANIC? We'll start to solder PCBs with OSP surface. What's the better type flux to solder the OSP? Thank you _____________________________ Juliano Ribeiro DATACOM Engenharia de Processos ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________