Machine Design #16: Designing Machines for a Clean Room — The Points That Get Overlooked

When people hear "a machine used in a clean room," many immediately think:

Use stainless steel. Cover it up tightly. Pick clean-room-grade components. Use low-dust grease.

Those ideas are not wrong.

But if your understanding stops there, it is not enough.

Designing a machine for a clean room is not about taking an ordinary machine and swapping a few parts to stainless steel. Nor does covering it up tightly turn it into a clean machine.

The biggest issue in a clean room is contamination control.

Contamination here is not only dust you can see with your eyes. It can be very small particles, oil mist, wear debris from sliding mechanisms, gas evaporating from plastic or adhesive, or even static electricity pulling dust toward the product.

So when designing a machine for a clean room, the designer has to look at the machine in a different way.

Not only asking:

"Does the machine run?"

But also asking:

"Does the machine generate dust as it runs?" "Does the dust it generates fly onto the product?" "Is there anywhere dust easily settles?" "Is it easy to clean?" "Is there any material that outgasses?" "Does static electricity attract dust or damage components?"

This article records the basic points when designing an automated machine for use in a clean room, aimed at machine designers who are meeting this kind of requirement for the first time.

1. A clean room is not just a clean room

A clean room is an environment where the number of airborne dust particles is controlled.

The requirement differs by industry.

For example:

Semiconductors
Electronics
Medical
Pharmaceuticals
Food
Optics
Batteries, film, precision materials

Each industry cares about a different type of contamination.

For semiconductors, even very tiny particles can cause product defects.

For medical or pharmaceutical use, besides dust there are questions of microbes, hygiene and cleanability.

For optics, dust or outgas settling on a lens surface can also ruin quality.

So before designing, do not ask vaguely:

"This machine is for a clean room, right?"

You need to ask more specifically:

What cleanliness class is required?
What is the product?
What particle size needs to be controlled?
Where in the line is the machine placed?
Are there chemicals?
Is there an ESD requirement?
Is there a low-outgas requirement?
Is grease allowed?
Is compressed air allowed?
Is a special material or surface treatment required?

A clean room is an environmental control system.

The machine you design is only one part of that system.

If the machine generates dust or disturbs the airflow, then no matter how good the clean room is, the product can still be contaminated.

2. First, understand the cleanliness class

The cleanliness class is the cleanliness level of the room.

Put simply, the stricter the class, the fewer airborne dust particles are allowed.

Today the ISO 14644-1 naming is commonly seen, for example:

Cleanliness class	A very short reading
ISO Class 5	Very clean, common in areas with strict requirements
ISO Class 6	Highly clean
ISO Class 7	The common clean level in many factories
ISO Class 8	Cleaner than a normal environment, but not extreme

Besides ISO class, some sites still use the old naming such as Class 100, Class 1,000, Class 10,000.

The point to remember is:

The stricter the cleanliness class, the more the machine design is constrained.

Not every machine needs the extreme design of high-grade semiconductor equipment. If the requirement is only ISO Class 7 or 8, the design can be more practical and the cost easier to control.

But if it is ISO Class 5, or an area near a sensitive product, the story is completely different.

Then every sliding mechanism, every wire, every air-exhaust location, every type of grease has to be looked at very carefully.

So before drawing the machine, confirm the cleanliness class first.

If you choose materials, actuators, cable carriers and grease before the cleanliness class is clear, you very easily have to redo it later.

3. A clean room lives on airflow

A very important point that beginners often overlook is airflow.

A clean room is not clean only because it has air filters.

It is clean because a continuous supply of clean air is fed in and carries dust out of the area to be protected.

In many clean rooms, clean air is blown from the ceiling down to the floor. This is usually called downflow.

When designing the machine, you do not create that main airflow.

The airflow belongs to the clean-room system.

The machine designer's job is:

Do not block the airflow, do not disturb the airflow, and do not place a dust source above the product.

It sounds simple, but in real design it is very easy to get wrong.

For example:

Placing a motor directly above the product area
Running a cable carrier across the cleanest area
Making a large cover that blocks the airflow from the ceiling
Creating many closed pockets so the air cannot sweep through
Leaving a dust-generating area upstream of the product

In a clean room, the position of a mechanism is not just a layout question.

It relates directly to the path the dust takes.

If a dust source is above the product, the dust can follow the airflow and fall onto the product.

If the machine has many large flat surfaces blocking the air, eddies or dead-air zones can form below them.

If dust is generated but has no way out, it settles and then flies back onto the product when the machine moves.

So when designing a clean-room machine, look at the layout in terms of airflow.

Not just from top-down like an ordinary layout.

4. The four principles of contamination control

You can remember a clean room by four basic principles:

Principle	Meaning
Do not bring in	Do not carry dust, oil or dirty material in from outside
Do not generate	The machine does not generate dust, debris, oil, dirty gas
Do not let settle	Do not create pockets, gaps, surfaces where dust collects
Be able to remove	If dust is generated, it can be extracted, filtered, cleaned

In machine design, the two most important points are usually:

Do not generate and do not let settle.

Because if the machine already generates too much dust, dealing with it downstream is very hard.

If the structure has too many pockets and gaps, then even with cleaning it is hard to keep clean long term.

Good design reduces contamination at the source.

Do not wait until the machine is finished and only then think about how to extract dust or add shielding.

At that point it is usually a patch-up fix — costly and ugly.

5. The biggest dust source is usually the moving mechanism

A stationary machine generates little dust.

A machine becomes dangerous when there is motion.

Common dust sources:

Linear guide
Ball screw
Bearing
Timing belt
Pulley
Gear
Cable carrier
Cable robot
Air cylinder
Seal
Plastic-to-metal sliding mechanisms
Friction clamping assemblies
Stop, stopper, cam, latch assemblies

Wherever there is friction, there is the potential for dust.

Wherever there is grease, there is the potential for grease to fling off or outgas.

Wherever plastic flexes repeatedly, there is the potential for wear and particle generation.

So when designing a clean-room machine, do not just choose actuators by force, speed and stroke like an ordinary machine.

You also need to look at:

Are there clean-room specifications?
Is there low-dust grease?
Is there vacuum suction inside the actuator body?
Does the seal generate a lot of dust?
Is the cable carrier a low-dust type?
Is the cable suitable for motion in a clean room?
Can the mechanism be placed away from the product area?

A machine that runs in a workshop does not necessarily run in a clean room.

6. Material: stainless steel is basic, but not the answer to everything

Talking about clean-room machines, many people think immediately of stainless steel.

It is true that stainless steel is used a lot.

The reasons are:

Low rust
Easy to clean
Stable surface
Peels less than paint
Suits many clean environments

But it does not mean that for a clean room the whole machine must be stainless steel.

Choose according to position and requirement.

For example:

Position	Materials often considered
Frame, cover near the product	SUS304, SUS316, electropolished stainless if high requirement
Parts contacting chemicals	SUS316, chemical-resistant plastic, ceramic as needed
Parts needing insulation	PEEK, PPS, PEI, epoxy glass, ceramic
Special sliding parts	PEEK sliding grade, PTFE, UHMW-PE, dedicated materials
Light covers, not near a strict area	Anodised aluminium, thin stainless, suitable panels

SUS304 is usually enough for many ordinary machines.

SUS316 is used when better corrosion resistance is needed, for example an environment with chemicals or higher humidity.

Anodised aluminium can be used in some positions, but needs care if there is friction, scratching or a strict particle requirement.

Engineering plastics such as PEEK can be very useful, but should not be overused because of the high cost.

The important point is:

The material must suit the position of use, not just suit the word "clean room."

7. The easier to wipe, the better

In a clean room, the machine surface does not only need to look nice.

It needs to be easy to clean and hard for dust to stick to.

Common shape mistakes:

Horizontal surfaces that are too large
Deep pockets
Sharp internal corners
Small grooves
Gaps between two covers
Many exposed screw heads
Exposed threads
Wiring placed where it is hard to wipe
Brackets stacked in many layers creating gaps

All of these are places where dust easily settles.

So when designing, prioritise:

Reducing horizontal surfaces
Giving covers a slight slope if needed
Rounding internal corners
Avoiding narrow gaps that cannot be wiped
Reducing the number of auxiliary brackets
Hiding or covering threads
Using easier-to-clean screw heads if the area is high-requirement
Avoiding a tangle of wiring around the product area

There is a very practical way to check:

Imagine you are the person who has to wipe the machine every day.

If there is a spot the hand cannot reach, the cloth cannot wipe, dust is visible but cannot be removed, then that design is not yet good for a clean room.

A clean-room machine does not only need to be clean at handover.

It has to be easy to keep clean during operation.

8. What is electropolished stainless for?

For high-requirement areas, stainless steel can be electropolished (in Japanese, denkai kenma).

Electropolishing makes the surface smoother at the microscopic level.

The main benefits:

Less particle adhesion
Easier to wipe
Better corrosion resistance
Fewer tiny dust-holding points on the surface
A surface that looks cleaner and is more stable

But electropolishing is not automatically good everywhere.

It increases cost.

And if the design has sharp corners, narrow gaps or an overly complex surface, the effect is not as hoped.

Electropolishing should be seen as part of the overall design.

It is not the case that you design carelessly and then electropolishing solves everything.

To get a clean surface, first the shape has to be reasonable.

Only then comes the surface treatment.

9. Timing belt is a dust source to be careful with

A timing belt is very convenient in an automated machine.

Cheap, easy to design, easy to replace, good for transmitting over a distance.

But in a clean room, a timing belt is a part to consider carefully.

Because a belt works by bending, meshing and rubbing against the pulley. After a while it can generate rubber debris or plastic dust.

If the belt is far from the product, the cleanliness requirement is not too high, and there is reasonable shielding and extraction, it can still be used in some cases.

But if the belt is near a clean product, especially above the product, you have to be very careful.

Alternatives to consider:

Direct drive
Linear motor
Clean-type ball screw
Clean-room-grade actuators
Motor placed away from the clean area, driving through a sealed mechanism
Shielding and dust extraction at the source

It is not that a clean room absolutely forbids timing belts.

But you must not use a belt out of habit as in an ordinary machine.

You need to look at the belt position, the airflow direction, the cleanliness requirement and the risk if the belt wears.

10. Linear guide and ball screw must be the right type

Linear guides and ball screws are very common mechanisms.

But in a clean room, they are also dust sources.

Because inside there are rolling balls, contact, grease and seals.

When choosing, look at:

Is there a stainless type?
Is there a low-dust type?
Is there a suitable seal?
Is there a self-lubrication unit?
What grease is the default?
Can low-dust grease be used?
Is dust extraction or vacuum suction required?

For ball screws, grease is a very important point.

Grease can be flung off when running at high speed.

If the grease is not suitable, it can become a contamination source.

So do not just write "apply grease" vaguely.

For a clean-room machine, the grease type must be clearly defined.

If using an off-the-shelf actuator, you must check in the catalogue whether it is really a clean-room type, or just an ordinary actuator with a cover.

11. Not all low-dust greases are the same

Grease used in a clean room must be chosen carefully.

It does not only need to lubricate well.

It must also:

Generate little dust
Fling off little
Evaporate little
Outgas little
Suit the temperature
Suit the load
Suit the seal material
Suit the environment of use

Linear-guide and ball-screw makers usually have their own clean-room or low-dust greases.

When designing, avoid writing too vaguely like:

Grease: standard

or:

Apply grease

For a clean-room machine, that kind of note easily causes mistakes during assembly or maintenance.

Write the grease type, maker, part number, or an equivalent requirement.

For example:

Low-dust grease for clean application

If the customer specifies a grease, follow the specification exactly.

A real fault is a machine that initially uses the correct grease, but after maintenance is wrongly greased with ordinary grease.

The machine still runs, but dust generation increases.

So the design has to account for future maintenance too.

12. Air cylinders and exhaust air are also an issue

Many people think an air cylinder is clean because it only uses compressed air.

But in a clean room, the exhaust air from valves and cylinders needs a careful look.

Compressed air can carry:

Oil
Water
Small dust particles
Debris from the seal
Contaminants in the piping

If exhausted straight into the clean room, it can cause contamination.

So when using compressed air in a clean room, look at:

Is the supply air clean enough?
Is there a suitable filter?
Is there oil mist?
Where does the valve exhaust go?
Is an exhaust cleaner needed?
Does the exhaust need to be collected and sent outside?
Is a clean-room-type cylinder needed?

In some cases, a dedicated exhaust filter can clean the exhaust air before releasing it into the environment.

But a filter clogs over time.

When it clogs, the cylinder speed can change.

So if you use an exhaust filter, plan for its replacement and inspection, and do not put it in a hard-to-maintain position.

13. A cable carrier can also generate dust

A cable carrier is a part that is very easily underestimated.

But it has a great deal of repeated motion.

The links rub against each other. The cables inside rub against each other. The air tubes rub against the wall. All of these can generate particles.

In a clean room, do not default to using an ordinary cable carrier.

Look at:

Is there a low-dust type?
Is there a clean-room type?
Is the cable inside suitable for motion?
Is a fluororesin cable jacket needed?
Is there a separator so the cables do not rub against each other?
Is the bend radius large enough?
Is the carrier above the product area?

If you only change the carrier but the cable inside is still ordinary PVC, the problem is not necessarily solved.

The wiring is also part of the dust-generating system.

For high-requirement areas, you may need cables that generate little dust, flex well, wear little on the surface and outgas little.

This point should be confirmed with the cable or actuator supplier from the start.

14. A fan is something to avoid in a clean room

In an ordinary machine, when it gets hot, you add a fan.

In a clean room, this way of thinking is very dangerous.

A fan can cause many problems:

Generate dust itself from the motor or bearing
Suck dust from elsewhere and blow it toward the product area
Disturb the room's clean airflow
Create uncontrolled airflow
Make particles fly back off the machine surface

So a clean-room machine usually prioritises a fanless design.

If cooling is needed, you can consider:

Increasing the heat-dissipation area
Placing the heat source away from the clean area
Using an easy-to-wipe heat sink
Conducting heat outward
Using water cooling if needed
Moving the control box outside the clean room if the layout allows

For motors, drivers and power supplies, plan for heat from the start.

Do not wait until the machine gets hot to add a fan.

In a clean room, adding a fan at the end is usually a sign that the initial design was not sound.

15. Static electricity is invisible but very dangerous

A clean room is not only about dust.

Static electricity is also a big issue.

Static electricity can cause two faults:

The first is ESD — an electrostatic discharge that damages electronic components.

The second is ESA — an electrostatic attraction force that pulls dust onto the product surface or machine parts.

There are spots that look very clean, but because they are charged, dust keeps sticking.

For machines used in electronics, semiconductors, film, thin plastics and small components, check ESD from the start.

Common measures:

Ground the frame correctly
Use ESD materials where the product is contacted
Use an ionizer if needed
Avoid strongly charging insulating materials near the product
Check the surface resistance of jigs, trays, guides
Control humidity if the process allows

But do not install an ionizer by feel either.

An ionizer also needs the right position, blow direction, discharge-pin maintenance and ion-balance control.

If installed wrongly, the effect is low or it disturbs the airflow.

16. Outgas: a clean material is not just dust-free

Outgas is gas or volatile matter released from a material.

Outgas sources can come from:

Plastic
Rubber
Adhesive
Paint
Grease
Wiring
Seals
Tape
3D-printed material
Some coatings

In some industries, outgas can settle on the product, lens, wafer or a sensitive surface.

The awkward thing is that outgas is not visible like dust.

The machine looks clean, is wiped clean, but can still cause defects if the material is unsuitable.

So for high-requirement environments, check:

Is the material low-outgas?
Is adhesive used near the product?
Is there ordinary rubber in the clean area?
Is the wiring suitable?
Does the grease evaporate?
Does the customer require outgas data?

A fairly common fault is using convenient materials from an ordinary machine — adhesive, rubber, sponge, tape, soft tube — that are not suitable in a clean room.

For a clean room, the auxiliary materials are as important as the main materials.

17. Maintenance must be designed in advance too

A clean-room machine does not only need to be clean when newly delivered.

It has to be clean after 6 months, 1 year, 3 years of operation.

For that, maintenance must be easy and generate little dirt.

When designing, ask yourself:

Is filter replacement easy?
Does adding grease require removing many covers?
Does replacing an actuator require opening the clean area?
Can a module be taken outside the clean room for repair?
Is there a spot where you have to reach your hand in very deep?
Are too many small screws used in an area that needs cleaning?
Is a special tool required inside the clean room?

Every time you open a cover, dismantle the machine, or use a tool is one more chance of contamination.

So a clean-room machine should be designed toward:

Easy access
Easy wiping
Easy module replacement
Little disassembly in the clean area
Maintenance positions outside the product area if possible
Maintenance instructions clearly stating grease, consumables, filters

Good design is not only running well on the acceptance day.

Good design is the maintenance person later not cursing you.

18. A quick checklist when designing a clean-room machine

Before finalising the design, do a quick check of the following points.

About the requirement

What is the cleanliness class?
Is the product sensitive to particles?
Is there an ESD requirement?
Is there a low-outgas requirement?
Are there chemicals, heat, steam or solvents?
Has the customer specified materials or grease?

About layout and airflow

Is the main airflow direction known?
Is a dust source placed above the product?
Does the cover block the downflow?
Is there a dead-air zone?
Is local exhaust needed?
Where does the compressed-air exhaust go?

About the moving mechanism

Is there a timing belt near the product?
Do the linear guide and ball screw have clean-room specifications?
Is the actuator a clean-room type?
Is vacuum suction provided for the actuator if needed?
Is the cable carrier a low-dust type?
Are the wiring and tubing suitable for motion in a clean room?

About material and surface

Is the stainless steel SUS304 or SUS316?
Is electropolishing needed?
Is anodised aluminium used in the right position?
Is the plastic low-outgas or ESD if needed?
Is there unsuitable rubber, sponge, adhesive or tape?
Is the surface easy to wipe?

About maintenance

Which grease is used?
Is the grease clearly noted on the drawing or maintenance document?
Is the exhaust-air filter easy to replace?
Can a module be replaced without opening too many covers?
Is there a spot where dust easily settles but is hard to clean?
Does the operator know the correct replacement consumables?

This checklist does not replace the customer's standard.

But it helps avoid very basic mistakes before sending the drawing or ordering components.

Conclusion

Designing a machine for a clean room is not just about switching the material to stainless steel.

Nor is covering the machine up tightly enough to make it clean.

The important point is to control contamination from the start.

Does the machine generate dust itself? Does the dust it generates fly onto the product? Is the clean airflow blocked? Is there anywhere dust easily settles? Does the material outgas? Is the grease suitable? Have the wiring, cable carrier, exhaust air and static electricity been looked at? Will future maintenance dirty the clean room?

With an ordinary machine, you mainly care that it runs correctly, is rigid enough, accurate enough and safe enough.

With a clean-room machine, besides those points, there is one more question to care about:

Can this machine maintain a clean environment while it is actually running?

That is the hard part.

Good clean-room design is not making everything very expensive.

Good design is knowing which area needs to be strict, which area can be simple, where the dust source is, and dealing with it from within the drawing — not waiting until the machine runs to fix it.

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