Dimensional Effect on Engineering Systems & Clean Room & Classification

Dimensional effect on Engineering
Systems
Clean room & Classification
Shehzad Shaikh & Samiran Tripathi

Dimensional effect on
Engineering Systems

Why Scaling Laws?
• Miniaturizing machines has been intensified in recent years as market demands
for:
• Intelligent, Robust, Multi-functional and Low cost
• Consumer products has become more strong than ever.
• The only solution to produce these consumer products is to package many
components into the product – making it necessary to miniaturize each individual
components.
• Miniaturization of physical systems is a lot more than just scaling down device
components in sizes.
• Some physical systems either cannot be scaled down favorably, or cannot be
scaled down at all!
• Scaling laws thus become the very first thing that any engineer would do in the
design of MEMS and microsystems.

Types of Scaling Laws
1. Scaling in Geometry:
• Scaling of physical size of objects
2. Scaling of Phenomenological Behavior
• Scaling of both size and material characterizations

Effects of scaling in microsystems
• Geometry
• Rigid-Body Dynamics
• Heat Conduction
• Electrostatic Forces
• Electromagnetic Forces
• Electricity
• Fluid Mechanics

Scaling in Geometry
● Volume (V) and surface (S) are two physical parameters that are
frequently involved in machine design.
● Volume leads to the mass and weight of device components.
● Volume relates to both mechanical and thermal inertia. Thermal inertia is
a measure on how fast we can heat or cool a solid. It is an important
parameter in the design of a thermally actuated device.
● Surface is related to pressure and the buoyant forces in fluid mechanics.
For instance, surface pumping by using piezoelectric means is a practical way
for driving fluids flow in capillary conduits.
• When the physical quantity is to be miniaturized, the design engineer must
weigh the magnitudes of the possible consequences from the reduction on
both the volume and surface of the particular device.

Scaling in Geometry
• If we let ℓ = linear dimension of a solid, we will have:
• The volume: V ∝ l3
• The surface: S ∝ l2
• Since volume, V relates to mass and surface area, S relates to
buoyancy force:
S/V = ℓ-1
A 10 times reduction in length
103 = 1000 time reduction in volume.
102 = 100 time reduction in surface area.

Scaling in Rigid-Body Dynamics
• Forces are required to make parts to move such as in the case of micro actuators.
• Power is the source for the generation of forces.
• An engineer needs to resolve the following issues when dealing with the design
of a dynamics system such as an actuator :
• The required amount of a force to move a part,
• How fast the desired movements can be achieved,
• How readily a moving part can be stopped.
• The resolution to the above issues is on the inertia of the actuating part.
• The inertia of solid is related to its mass and the acceleration that is required to
initiate or stop the motion of a solid device component.
• In the case of miniaturizing these components, one needs to understand the
effect of reduction in the size on the power (P), force (F) or pressure (p), and the
time (t) required to deliver the motion.

Scaling in Electrostatic Forces
• The corresponding potential energy is
When two parallel electric conductive plates is charged by a
voltage →Electric potential field
U=-1/2(CV2)=-εo εRWL
2d
V2
Let ℓ = linear scale of the electrodes, we will have:
εo , εr ∝ ℓ 0 and W, L and d ∝ ℓ 1
The scaling of voltage, V can be approximated by the Paschen’s effect illustrated as:
We will use a linear scaling for the voltage:
V ∝ ℓ 1
from which we get the scaling of the Potential energy, U to
be:
Scaling: A 10 times reduction of linear size of electrodes
→ 103 = 1000 times reduction in Potential energy!!

Scaling in Electromagnetic Forces
• Electromagnetic forces are the principle actuation forces in
macroscale, or traditional motors and actuators.
• Working principle: An electromagnetic force, F is generated when a
conducting wire with passing electric current , i subjected to an emf is
exposed to a magnetic field B with a flux, dΦ

Scaling in Electricity
• Electric Resistance:
R= ρL /A∝ (ℓ⁻¹)
in which ρ, L and A are respective electric resistivityof the material, the
length and across-sectional area of the conductor
• Resistive Power loss
P=V²/R ∝(ℓ)⁻²
Where V is the applied voltage

Scaling in Fluid Mechanics
• Two important quantities in fluid mechanics in flows in capillary
conduits:
• Volumetric Flow, Q:
Q= πa⁴∆P/8µL
Where Q ∝ S⁴
This implies that a reduction of 10 to the radius, will lead to a 10000
times reduction in volumetric flow.

• Pressure Drop, ∆P:
From the same Hagen-Poiseuille’s equation, we can derive:
∆P= −8µVₐᵥₑL/a² Leads to: ∆P/L ∝ a⁻³
Scaling: A reduction of 10 times in conduit radius →10³= 1000 times
increase in pressure drop per unit length

Scaling in Heat Conduction
• Two concerns in heat flows in MEMS:
• A. How conductive the solid becomes when it is scaling down?
This issue is related to thermal conductivity of solids. Equation (5.51)
indicates the thermal conductivity, k to be:
k=1/3CV λ ∝(ℓ⁻³)(ℓ¹)(ℓ³)=(ℓ¹)
• B. How fast heat can be conducted in solids:
This issue is related to Fourier number defined as:
Fo= αt/L² Leads to : t= Fo /α L² ∝(ℓ²)
Scaling: A 10 times reduction in size →10²= 100 time reduction in time to
heat the solid.

What is a Cleanroom?
• A specially designed & constructed room in which; the air supply, air
distribution, filtration of air supply, materials of construction, and
operating procedures, are regulated to control airborne particle
concentrations to meet appropriate cleanliness levels.

What is a “Particle”?
• A Particle is a very small discrete mass of solid or liquid matter,
usually measured in microns.
• A micron is 1/1,000,000 of a meter.
• A human hair is 60 - 90 Microns.

Particle Size Comparison
• An ISO Class 8 Cleanroom will have a maximum of 70 particles @ 5.0
Micron and a maximum of 100,000 @ 0.5 Microns / Cubic Foot
• (Actually measured in Cubic Metres in ISO)

Cleanroom Classification Particles per Cubic
Meter
ISO 14644 0.5 Micron 5 Micron
3 35 N/A
4 352 N/A
5 3,520 29
6 35,200 293
7 352,000 2,930
8 3,520,000 29,300

Where does Contamination Come From?
• Equipment, Material & Processes in the Cleanroom produce
contamination.
• The largest single controllable source of contamination enters the
Cleanroom with the Associates that work there.

How do we Control Particles
• Isolation - Particles may be isolated by containing them at the source
of generation.
• This is difficult as the Processes and Associates in the Cleanroom are
the largest source of contamination.

How are Particles Controlled?
• Dilution - Particles are
captured by filtration, and the
total space volume is diluted
by clean air.

HEPA / ULPA Filters
• This is a Ceiling
Mounted HEPA
Filter.
• High Efficiency
Particulate Air
Filters, range from
99.97% to 99.995%
Efficient

ULPA Filters (Ultra-low particulate air)
• These are Ceiling
Mounted ULPA
Filters.
• These High
Efficiency
Particulate Air
Filters are 99.9995%
Efficient

Typical Air Change Rates
ISO Class Air Changes Per Hour
4 720+
5 500-720
6 60-100
7 30-50
8 20-30

Associate Contamination
0.5 Micron Particles /
Minute
Street Clothing Bouffant & Frock Overall & Hood
Sitting 302,000 112,000 7,450
Swinging Arms 2,980,000 300,000 18,700
Twisting Upper Body 850,000 267,000 14,900
Walking 2,920,000 1,010,000 56,000

References
• MEMS and Microsystems: Design, Manufacture, and Nanoscale
engineering,” 2nd Edition, by Tai-Ran Hsu, John Wiley & Sons, Inc.,
Hoboken, New Jersey, 2008
• IEST - Recommended Practices & ISO Documents

Dimensional Effect on Engineering Systems & Clean Room & Classification

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