Collaborative cleaning process innovations from managing experience and learning curves
deflected spray carried into the chemical
isolation section. The front isolated area
is equipped to collect and drain wash
chemistry removed from both the air
knives and deflection back into the wash
tank.
The next management tool used in a
well designed chemical isolation module
is the wet spray section. This wet spray
ensures the dilution of chemistry that
remains in and around tightly spaced
components and underneath low standoff
devices missed by the isolation air knives.
This wet section manifold is powered from
the rinse module pump, which provides
Figure 7. Chem iso bulkhead with drain to wash holding tank.
high quality third use water for wet
isolation. The slipstream from the rinse
chemistry): To achieve a tight quality range,
improves rinse quality and prolongs carbon
wash tank chemistry control is critical.
and ion exchange purification media. This
A properly balanced wash tank provides
cascade function allows the rinse tank to
cleaning consistency over time and
be replenished and regenerated by the
increases the life of the chemistry. New
gravity cascading final rinse.
generation cleaning fluids work well at
The last important section of the
lower cleaning concentrations and readily
chemical isolation is another set of air
condense, which reduces ventilation
knives above and below the conveyor belt.
losses. The benefit for users is much lower
These air knives mechanically strip the
cleaning material consumption, which
wet section spray from the circuit board
equates to lower cost of ownership. For
and conveyor belt before entering the
example, when running a 10% wash
Figure 8. Mist arrestor.
rinse section. This prevents any diluted
concentration, only 1-2% cleaning fluid
chemistry from reaching the recirculating
additions are needed to maintain the 10%
rinse and is especially important when
concentration over time.
consistency over time and increase wash
running a closed loop rinse. Even if the
Typically an inline will consume 3-10
bath life (Figure 9).
rinse tank is not closed looped, chemistry
gallons of wash fluid per hour of pump
Automated monitoring and control:
carryover can lead to rinse section foaming
time operation. Since new generation
More and more high reliability products
and excessive consumption. When close-
cleaning chemistry losses are minimized
that require full time data logging of
looping the rinse, the chemical isolation
by the cleaning material design, very little
the monitoring and control of the wash
spray section is a must to ensure DI filter
cleaning chemistry is needed to maintain
bath concentration are being cleaned.
columns are not degraded due to chemistry
wash concentration. The problem: without
These capabilities are being driven by
contamination.
a consistent add of cleaning material with
governmental agencies and OEMs that
Air management—ventilation: Airflow
water additions, excessive amounts of
require product traceability all along the
management prevents steam from exiting
water can be added over time, diluting the
manufacturing process. Process control
the entrance or exit ends of the machine.
wash bath concentration. Without the
systems with these capabilities can be easily
Cleaning machines that run wash
consistent addition of wash chemistry with
integrated with the machine wash tank.
chemistries require a separate exhaust
make-up water additions, the wash tank
Proportional injections of chemistry can
plenum for managing the wash section and
will eventually lose strength and cleaning
be accomplished based on feedback from
a separate exhaust plenum for managing
performance will drop off. To prevent this
automated monitoring methods. This
the dryer sections. The air must be
condition, a chemical proportioning device
automation reduces the requirement for
balanced to provide a slight negative draw
should be used to maintain the wash tank
manual concentration monitoring freeing
at both the entrance and exit ends of the
concentration to process specifications.
process engineers for other important
machine. Excessive air draw in the wash
Proper additions increase cleaning
duties. The process control system will
section can cause wash fluid fumes to be
evacuated to the roof. Excessive air draw
from the dryer vent can draw wash fluid
fumes into the rinse section, which can
cause rinse foaming. Properly balanced,
the system does not fill the room with
wash odors and manages the airflow so
that minimal wash fluid is evacuated. Mist
arrestors are commonly used to condense
the wash fumes, which allows much of the
Poor Wash Control Proper Wash Control
cleaning solution to be returned to the
wash tank (Figure 8).
Figure 9. Process control illustration.
Fluid control (controlling the wash
32 – Global SMT & Packaging – June 2009
www.globalsmt.net
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