There isn't really an answer to your question.
Wood rosin - colophony - is a natural product so it will vary in composition
broadly according to the part of the world it was grown in. Other natural
resins can also vary.
Synthetic resins are of course quality controlled chemicals, but
manufacturers are free to choose which ever one they like. So though you
could say synthetic resins are more consistent than natural rosins, you have
a greater choice to consider than the simple pair implied by your question.
You would anyway have to question whether any natural compositional
variations are significant with respect to fluxing/residue properties.
More importantly the basic premise of your question may not hold. Old style
MIL fluxes were certainly rosin based, but modern fluxes are much more
likely to contain a mix of rosin and resins however classified. 
The RO or RE classification refers only to the largest single ingredient. So
to take an extreme theoretical example: imagine a flux made using 40% Rosin,
30% Resin A and 30% resin B. This could be classified RO even though it was
60% synthetic resins. 
The use of different resins extends the performance envelope of the flux in
specific areas beyond that of rosin on its own. Conversely very few
synthetics are as effective as rosin in all areas. Even some so called rosin
free fluxes can contain some rosin derivatives.
The old truism "There is no substitute for rosin" is still holding up pretty
well.
Myself I just love it that one of the most advanced manufacturing industries
in the world using some of the most complex processes ever devised depends,
when it comes down to it, on wood sap!






Regards

Mike Fenner 
Bonding Services & Products
T: +44 [0] 1865 522 663 E: [log in to unmask]

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Garcia, Rigo
(GSFC-300.0)[MANTECH SRS TECHNOLOGIES]
Sent: Friday, February 17, 2012 9:32 PM
To: [log in to unmask]
Subject: [TN] Are Rosin and Resin Fluxes TRULY equivalent?

Hi TechNetters!

Hard to believe specially for High Reliability assemblies where so many
variables can interact to lead to contamination problems. Are Rosin and
Resin Fluxes TRULY equivalent?

What do the experts have to say? Any data? White papers?

Have a great weekend! :-)

Rigo Garcia

Sr. Quality Assurance Engineer
Workmanship Standards, Code 300 
NASA, Goddard Space Flight Center
Greenbelt, MD  20771
Phone. (301) 286-6129
Fax.       (301) 286-6576


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