Collaborative cleaning process innovations from managing experience and learning curves
available fluid and critical soil loading
limitation. Critical soil loading represents
the contamination level at which cleaning
is not longer acceptable. The dynamics
at work when running an inline cleaning
process find losses through evacuation
(ventilation effects) and drag-out. As soil
is introduced, the wash holding tank
will start to accumulate contamination.
Larger wash tank volume provides a
wider processing window for holding
the flux contaminants introduced to the
Figure 5. Flux dam illustration.
cleaner. As water and wash chemistry are
replenished, the ideal condition occurs
the residue to create an opening for the
when the cleaning material additions
wash fluid to flow under the component.
maintain a wash tank volume below the
Hard flux residues take longer to dissolve
critical soil loading limitation.
than do soft flux residues, which increases
Fluid Management: One of the
wash complexity. The static cleaning rate
risk factors from high fluid flow, high
(dissolution in the absence of impingement
impingement pressure and directional
energy) of the wash chemistry is driven
force nozzles is spray deflection into the
by the cleaning material compatibility
chemical isolation section. Shorter wash
with flux soil, rate of dissolving the flux
sections have less distance from the spray
soil, concentration, part fixturing and
manifold to the chemical isolation section.
Figure 6. Wash tank illustration.
wash temperature effects. The cleaning
Deflecting wash fluid into the chemical
material static cleaning rate may vary on
isolation section can cause high wash
different flux residues. To address these
chemistry consumption. To address this
in the rinse sections. Cleaning data studies
complexities, best in class cleaning material
issue, larger wash sections provide distance
show that high levels of fluid across the
designs are formulated to work on most
from the final spray manifold to the
board surface decrease needed cleaning
flux residue types, but the rate varies for
chemical isolation section entrance. Wash
time. Directional forces that provide a
both hard and soft flux residues, with the
spray deflected into the chemical isolation
360° impingement pattern during the
key variable representing time in the wash
zone must be captured and returned to the
wash exposure decreases time in the
stage.
wash tank. Chemical isolation innovations
wash. Maintaining pressure with flow also
Fluid Storage: The size of the wash
dramatically reduce wash chemistry
decreases the amount of time required in
holding tank is often overlooked in the
consumption, and good fluid management
the wash section.
cleaning equipment design (Figure 6). The
designs are the keys to reducing chemical
Wash impingement effects can be
wash tank surface area (width x length) and
consumption and operating cost.
generated using various nozzle and
tank volume (x depth) are an important
The chemical isolation module
pump technologies. To improve cleaning
cleaning machine design criterion. High
provides the ultimate fluid management by
efficacy, boards are initially sprayed in
fluid flow nozzles increase the level of
separating the wash and rinse sections. The
the pre-wash section using fan jets. The
wash turns per minute of operation. If
conveyor belt, circuit cards and fixtures
pre-wash zone brings the circuit card
the wash tank capacity is too small, rapid
are wetted with the cleaning fluid. As
up to process temperature, which starts
tank turnover can cause air bubbles to
these wetted components leave the wash
the flux softening process. In the wash
migrate deeper into the wash tank. When
section, they are carried into chemical
section, nozzle jets provide uniform wash
this condition exists, foam build is greater
isolation section. One of the objectives of
coverage. Board geometry, density and
than foam break. Additionally, rosin/resin-
the chemical isolation section is to remove
component types are impinged upon using
based flux soils saponify with the reactive
and return the wash solution from the
a combination of nozzle technologies
agents in the cleaning material, which can
conveyor belt, circuit boards and fixtures
that provide various levels of fluid
couple or emulsify the anti-foam minor
back to the wash tank. Recent equipment
flow, pressure at the board surface and
ingredients. The combination of these two
innovations strip off the wash fluid from
directional forces. Printed circuit boards
factors allows air to eventually reach the
parts as well as capture defected wash spray
with increased density and component
pump intake with the result of a highly
that enters the chemical isolation section.
shadowing require a longer wash time to
stable foam condition. Foaming leads
This important economic function reduces
allow wash fluid to penetrate blind gaps.
to pump cavitation or micro air pockets
chemical usage and saves operation cost.
To remove all flux residues under gaps
which reduce the machine’s operating
At the entrance of the chemical
less than 2 mils, time in the wash and
spray pressures, the effectiveness of the
isolation section, an air knife above and
wash temperature are critical parameters.
wash process and costly mechanical pump
below the conveyor belt removes wash
The wetting effects of flux during the
seal failure.
fluid mechanically from the conveyor belt,
reflow soldering process cause the flux to
Wash Bath Life: The volume of the
circuit boards and fixtures. A bulkhead is
penetrate under small component gaps
wash tank is also important in maintaining
positioned within the chemical isolation
and create a flux dam (Figure 5). To break
a long wash bath life. The affinity of the
section after the air knife but in front
the flux dam, the cleaning fluid and
wash fluid to hold another substance in
of the chemical isolation spray rinse
impingement energy must first dissolve
solution is bound by the volume of the
manifolds (Figure 7). The bulkhead isolates
30 – Global SMT & Packaging – October 2009
www.globalsmt.net
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