The term "Resin" describes a group of chemicals which includes natural
materials such as shellac from beetles and synthetic materials such as
epoxies. The natural material we are most familiar with in soldering is
rosin - aka colophony - which is extracted from pine trees in much the same
way as rubber is tapped. Some of the first soldering fluxes were made from
rosin which has nearly all the attributes needed for electronic soldering.
It does not have quite the oxide removal properties to be totally
satisfactory and so more active chemicals are blended with it, these are
known as activators. The amount and type added is controlled to avoid too
much activity which can lead to corrosion. This gave us the old style R
(pure rosin) RMA (mildly activated and RA (fully activated) designations.
You can tell the military was involved in these because mildly activated
rosin would more naturally be abbreviated MAR rather than RMA. :)
.
These old style specs were based on composition, basically they said if you
use these materials in these proportions and they meet compositional tests
(e.g. less than a certain amount of activator or leachable acid then they
were considered safe. In other words pragmatic based on a few decades of
finding out what worked and what didn't.
Modern no clean technology requires more than just chemical and electrical
properties, clear light residues for example and these are more easily met
by using other resins. If you look at current specifications you will see
that the no clean classification is the same for rosin or resin containing
materials. Whether or not a flux meets modern specs is not so much concerned
with what is in the flux as supplied, but what the residues do after reflow.
So the test criteria are surface insulation resistance (SIR) of reflowed
test pieces and so on. The post solder tests for no cleans were based on how
RMA fluxes behaved. The RE and RO in flux designations is really now for
information only and help provide continuity from the previous spec regime
and flux types to the ones we use now. [Also for those still doing legacy
work for those requiring MIL spec fluxes.]
This explanation is somewhat oversimplified for clarity. Hope it helps.

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 Graham Collins
Sent: Tuesday, April 30, 2013 2:13 PM
To: [log in to unmask]
Subject: [TN] Flux classification question

Flux gurus, can you tell me the difference between ROLO and RELO fluxes?

(Dewey, I know - the second letter is different, that isn't helpful!)

Is a RELO more active or less?  Or does the E mean something else?

-- 
regards,

Graham Collins
Senior Process Engineer
Sunsel Systems
(902) 444-7867 ext 211


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