This article discusses the mechanisms
of particle deposition onto cleanroom
surfaces. The main mechanism
for particles above about 0.5μm is
gravitational settling. Turbulent
deposition and electrostatic attraction
can also occur at all particle sizes, and
for particles below 0.5μm Brownian
diffusion is important. Measurements
of particle deposition rates (PDRs) were
made of particles ≥ 0μm on witness
plates orientated in different directions
and exposed in different ventilation
conditions, and it was concluded that
over 80% of particles were deposited
by gravitational sedimentation, and
probably more than half of the
remainder by turbulent deposition
