Rosin Paste Fluxes are intended to be used to
reduce solder balling, and bridging. The proper flux allows for proper solder
flow and increased wetting of desired areas.
Rosin or colophony is a natural product that is
extracted from the stumps or bark of pine trees. The composition of rosin varies
from batch to batch, but a general formula is C19H29COOH. It consists mainly of
abietic acid (70 to 85 percent, depending on the source) with 10 to 15 percent
pimaric acids. Rosins contain several percent of unsaponifiable hydrocarbons;
for rosin flux removal, saponifiers (a form of alkaline chemical to make the
water soapy) must be added.
Rosin flux is composed primarily of natural resin extracted from the oleoresin
of pine trees and refined. Rosin fluxes are inactive at room temperatures but
become active when heated to soldering temperatures. They are naturally acidic
(165 to 170 mg KOH per g equivalent). They are soluble in a variety of solvents
but not water. This is the reason for using solvents, semiaqueous solvents or
water with saponifiers to remove them.
The melting point of rosin is 172°C to 175°C (342°Fto 347°F), or just below the
melting point of solder (183°C). A desirable flux should melt and become active
slightly below the soldering temperature. A flux is not effective if it
decomposes at soldering temperatures, however. This means that synthetic fluxes
can be used at higher temperatures than rosin fluxes, because the former
decompose at higher temperatures. In general, rosin fluxes are weak, and to
improve their activity (fluxing action), the use of halide activators is
The general formula for oxide removal by rosin is:
RCO2H + MX = RCO2M + HX
where RCO2H is rosin in the flux (C19H29COOH mentioned earlier)
M = Sn, Pb or Cu
X = oxide, hydroxide or carbonate
As mentioned earlier, rosin fluxes are also referred to as rosin (R), rosin
mildly activated (RMA) and rosin activated (RA). The various categories of rosin
fluxes differ in the concentration of the activators (halide, organic acids,
amino acids, etc.). R and RMA types are generally noncorrosive, hence safe. R
and RMA fluxes are not even cleaned in some applications even though they are
not classified as no-clean. However, without cleaning, assembly reliability may
be compromised because the sticky rosin can attract dust and harmful
contaminants in the field during service.
The fluxes described here require cleaning. To get away from cleaning, many
companies have shifted to no-clean flux, which will be the focus of my next
Where to buy gum rosin or pine rosin?
Where to buy Rosin?
Our rosin products are available for sale at
www.ChemicalStore.com. For large orders please call in advance and verify the
availability, wholesale discounts and shipping options. If you cannot find any
product in the online store of your choice, please use the search option of the
store or call (973)405-6248 for further assistance.
All orders will be shipped from our
warehouses in United States (USA), Canada or United Kingdom. We ship worldwide
to most countries including U.S., Canada, Australia, United Kingdom, New
Zealand, Germany, France, Netherlands, and many other countries.