Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.8 Electronic industry 913
14.8.4.1.3 Semi-aqueous cleaning
Figure 14.8.13. Diagram of a semi-aqueous cleaning process with
ZESTRON � FA.
A process that has found widespread
use in practice is
semi-aqueous cleaning with
ZESTRON � FA. This cleaner was
especially developed for removal
of no-clean soldering fluxes in ultrasonic
batch or spray under immersion
cleaning systems. It is
used in the cleaning bath, rinsed
with demineralized water, and
then dried with hot air (see
scheme in Figure 14.8.13.).
The carried-in flux constituents
can be removed by a flux
absorber system to ensure the
cleaning medium maintains a constant quality. Cartridge filters also remove precipitated
flux residues and particles. Two cascaded rinsing units - a pre-rinse and a fine rinse - follow
the wash stage. The rinsing water contaminated with carried-over cleaning medium is
passed through different sized particle filters, mixed-bed ion exchangers, and activated carbon
filters. The quality of the rinsing water can be continuously monitored by conductivity
measurement to establish its residual ion content. The conductivity value should be below 1
µS/cm.
The complete process in based on a closed-loop principle. Consequently, the cleaning
process merely liberates those substances that are to be removed from the pc-boards (i.e.,
soldering flux residues). Closed-loop operation is not only advisable for ecological reasons,
but is also a very sound economic proposition as it significantly minimizes process costs.
14.8.4.1.4 Aqueous cleaning in spray in air cleaning equipment
Low pressure spray in air batch cleaning systems (see Figure 14.8.14) can be attractive
propositions for users who only have a low volume of pc-boards to clean and are required to
furnish proof of a specified cleaning process to their customers. The water-based mildly alkaline
cleaning agent VIGON � A200 was specifically developed for this application.
High-pressure spray in air in-line cleaning
processes that remove flux residues from
PCBs, are often employed by manufactures
to clean large quantities of boards. This still
represents the most economical way to clean
large quantities of PCBs. Especially for contract
manufactures that are required to clean
different types of PCBs, often with several
different flux residues.
The parts to be cleaned are fed, one after
the other, into a continuous spray cleaner
Figure 14.8.14. Diagram of an aqueous in-line cleaning
process with VIGON � A200.
where they pass through the different process
stages indicated in Figure 14.8.15. The