Handbook of Solvents - George Wypych - ChemTech - Ventech!

910 Martin Hanek, Norbert Löw, Andreas Mühlbauer
• Relatively inexpensive (although explosion protecting oftentimes significantly
increases the cost of the machine),
• Easy to use,
• A large number of options (add-ons) available (in-line filtration, closed loop water
recirculation, programming options, etc.),
• Do not require as much media as other types of stencil cleaners, because they do not
require total immersion of the stencil,
• The stencil is also washed, rinsed, and dried in the same chamber, thus eliminating
the need to move the stencil around manually.
Disadvantages include the sometimes large footprint that results from having to provide
up to three separate chambers (wash, rinse, and stencil), and the sometimes inadequate
agitation (spray pressure) generated by the machine. This can make it difficult to clean
fine-pitch apertures.
Spray under immersion cleaning equipment
In spray under immersion equipment,
the stencil is placed into a bath (immersed)
containing the cleaning medium. The medium
is then recirculated using submerged
spargers to provide agitation to the stencil
surface. A separate chamber is then used for
rinsing and drying. Advantages of this type of
machine are that it is:
• Most gentle on the stencil, and
• The capital expense is relatively low.
Figure 14.8.9. Scheme of typical spray under immersion
batch cleaner.
However, because of the low pressure,
cleaning cycles may require longer cleaning
times. Also, the size of the machine and the
quantity of cleaner required are dictated by the size of the stencil to be cleaned.
Ultrasonic cleaning equipment
Ultrasonic machines, as the name
implies, use ultrasonic “vibratory” energy
to clean stencils. The stencil is immersed
in a bath containing the
cleaning medium, and exposed to ultrasonic
energy. The ultrasonic frequency
varies, but is typically between
40 and 100 kHz. Options for the ultrasonic
cleaning machine include overflow
recirculation of the medium, as
well as spray under immersion jets to
Figure 14.8.10. Scheme of typical ultrasonic batch cleaning
equipment.
aid cleaning and bath agitation. The
equipment also varies greatly in size
(from tabletop models to large footprint
models that include rinsing baths,
air dryers, and robot arms). Advantages of this unit are that:
• The ultrasonic energy is much better suited to cleaning fine pitch openings, and