Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.8 Electronic industry 915
14.8.4.2.1 Water-free cleaning processes using HFE (hydrofluoroethers) in
combination with a cosolvent
The cleaning process:
A cosolvent cleaning process is one, in which the cleaning and rinsing solvents are of significantly
different composition. For example, in semi-aqueous systems (see Cleaning Technologies
on the PCB Assembly Shop Floor (Part II) in EPP Europe, October 1999) cleaning
is done with organic solvents and water is used for rinsing. In the cosolvent cleaning process,
cleaning is accomplished primarily by the organic cosolvent, and rinsing is effected by
a fluorochemical. Typically, in cosolvent systems, the boil (wash) sump contains a mixture
of cosolvent and fluorochemical rinsing agent. The rinse sump normally contains essentially
100% fluorochemical rinsing agent.
Referring to Figure 14.8.16,
a cosolvent process operation can
be summarized as follows. Printed
circuit boards containing flux residues
are immersed into the boil
sump, which contains a mixture of
cosolvent and fluorochemical
rinsing agent, typically about
equal volumes of each. After being
cleaned in the boil sump, the
substitutes are immersed in the
rinse sump, which contains nearly
Figure 14.8.16. Typical vapor degreasing equipment.
100% fluorochemical.
The primary function of the
rinse sump is to remove the
fluorochemical/cosolvent mixture and the soil dissolved in it. Following immersion in the
rinse liquid, the parts are moved into the vapor phase for a final rinse with pure
fluorochemical vapor. Finally, the parts are lifted into the freeboard zone, where any remaining
fluorochemical rinsing agent evaporates from the parts and returns to the sump by
condensation from cooling coils. At this point, the cleaning cycle is complete and the parts
are clean and dry.
Furthermore, pure Novec TM HFEs can be used for the removal of light soils,
halogenated compounds like fluorinated greases or oils, and other particles.
The increasing popularity of the cosolvent process is mainly due to its flexibility in allowing
independent selection of both the solvating and rinsing agents that best meet the
needs of a particular cleaning application. The fluorochemical cosolvent process is even capable
of defluxing components with very complex geometry due to the advanced physical
properties of the cosolvent.
The cleaning chemistry:
Novec TM hydrofluoroethers (Novec TM HFEs) are rapidly becoming recognized as the solvents
of choice for superior cleaning in the electronics and precision engineering industries.
The combined properties of these new materials have proven to be very effective alternatives
to ozone depleting substances (ODSs) like the previously mentioned CFCs and
HCFCs. The new developed chemical compounds methoxyfluorobuthylether (HFE 7100)
and ethoxyfluorobuthylether (HFE 7200). HFE rinsing agents can be used in combination