3 Biggest Threats to Semiconductor Cleanrooms

3 Biggest Threats to Semiconductor Cleanrooms

Work involving semiconductors requires sensitive processes and a highly controlled environment. While the right cleanroom can help achieve this control and minimize risks, there are still a number of factors that threaten semiconductor cleanrooms

Let’s take a look at how these factors affect the semiconductor industry and how to design cleanrooms to defend against them.

 

3 Biggest Threats to Semiconductor Cleanrooms

 

Humidity, static electricity, and human contamination. Although they may seem harmless when encountered in day-to-day life, in semiconductor cleanrooms, these three factors can pose significant threats to productivity, products, and staff.

 

#1 Humidity in Semiconductor Cleanrooms

 

Many products developed, manufactured, and tested in semiconductor cleanrooms are sensitive to moisture, so control of relative humidity (RH) is crucial. Most semiconductor cleanrooms must maintain RH at 35-65% in addition to temperatures at 70 degrees Fahrenheit or lower.

Even within that range, fluctuating humidity can present many threats — both to productivity and product quality — from inconsistent bake-out times, evaporation of solvents, surface swelling and corrosion, and generally control during production.

To control and maintain RH, semiconductor cleanrooms require powerful HVAC systems to treat the air before it’s filtered into the space. These HVAC systems are often independently dedicated to the cleanroom to minimize risk of contamination.

 

#2 Static Electricity in Semiconductor Cleanrooms

 

Static electricity on a microscopic level is a leading cause for defects of silicon wafers and semiconductors. Static corrupts materials by drawing and adhering fine particles to the products’ surface, which can cause product rejection or failure.

Electrostatic discharge (ESD) can also pose a serious threat to worker safety. When static charges are allowed to build up, they can release suddenly in an uncontrolled manner and harm employees — either through electric shock or involuntary movement. 

Preventing static buildup starts with cleanroom design. Conductive materials are often more effective than insulative materials in sensitive applications like semiconductor cleanrooms. Conductive materials allow electrons to flow quickly away from areas where they could build up and direct them safely to ground.

 

#3 Human Contamination in Semiconductor Cleanrooms

 

Maybe the biggest threat to semiconductor cleanrooms is the human factor. From generating ESD to the tendency to shed contaminating particles, controlling humans in the cleanroom is one of the most challenging aspects of cleanroom design, yet also one of the most essential.

Gowns, gloves, hearing protection, and other PPE work to protect semiconductor processes from the human element, but they also protect workers from dangers in the cleanroom setting in accordance with ANSI and OSHA requirements. These threats include chemical exposure, fumes, static charges, and more. 

Even with a thorough gowning protocol, semiconductor cleanrooms require extra protection against airborne contamination. In addition to powerful HEPA filters in ceiling units, semiconductor cleanrooms may require ULPA filters to capture more and smaller particles, as well as the placement of filters in the make-up air handler and return air handler.

 

Semiconductor Cleanroom Design Considerations

 

The manufacturing and development of semiconductors and related products is highly sensitive and requires every system in the cleanroom to work together in order to comply with strict standards of cleanliness. Most semiconductor cleanrooms fall within ISO Class 5 or cleaner requirements, which means they have some of the most stringent particle count requirements of any other industry.

As factors like humidity, static electricity, and human contamination continue to threaten cleanroom processes and personnel, semiconductor cleanroom design must be able to address each one: using a powerful HVAC system, multi-stage filtration system, and antistatic and conductive materials. 

No matter the environmental factors you need to control, Angstrom Technology can engineer the ideal cleanroom for your application. Let us use our extensive industry experience to guide you through the design process. We can deliver the turnkey cleanroom solution you’ve been searching for. Give our team a call to get started.

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Importance of Cleanroom Airflow Uniformity

Importance of Cleanroom Airflow Uniformity

Cleanrooms are designed to maintain strict control over environmental factors, but they’re only effective if they have an expertly designed airflow pattern to help them reach the desired cleanliness level and ISO classification standard. ISO document 14644-4 describes airflow patterns to be used in cleanrooms at the different classification levels in order to maintain strict airborne particle counts and cleanliness. 

Cleanroom airflow must allow the air within the cleanroom to be completely changed to remove particles and potential contaminants before they can settle. In order to do this properly, the airflow pattern must be uniform — ensuring every part of the space can be reached with clean, filtered air.

To break down the importance of cleanroom airflow uniformity, we need to start by looking at the three main types of airflow in cleanrooms.

 

3 Types of Cleanroom Airflow Patterns

 

Cleanroom airflow can be unidirectional, non-unidirectional, or mixed — a combination of both. The best cleanroom airflow type will depend on the cleanroom classification. Generally, cleanrooms of an ISO Class 6 or greater can use a mixed or non-unidirectional airflow pattern, while ISO Class 5 (or cleaner) cleanrooms rely on unidirectional airflow.

 

#1 Unidirectional Cleanroom Airflow

 

This type of cleanroom air moves in one direction across the room, either horizontally or vertically from fan filter units to the exhaust system that removes “dirty” air. Unidirectional flow requires as little disturbance as possible to maintain a uniform pattern.

 

#2 Non-Unidirectional Cleanroom Airflow

 

In a non-unidirectional airflow pattern, air enters the cleanroom from filter units located in multiple locations,  either spaced throughout the room or grouped together. There are still planned entrance and exit points for air to flow along more than one path.

Although air quality is less critical compared to unidirectional airflow cleanrooms, special attention should be paid to make sure air is changed thoroughly, minimizing the potential for “dead zones” within the cleanroom. 

Dead zones are areas where air is turbulent or not being changed and may result in deposited particles or a buildup of contaminants.

 

#3 Mixed Cleanroom Airflow

 

Mixed airflow combines both unidirectional and non-unidirectional airflow. Unidirectional airflow may be used in specific areas to boost protection around working areas or more sensitive materials, while non-unidirectional airflow still circulates clean, filtered air throughout the rest of the room.

mixed cleanroom airflow

 

Why Cleanroom Airflow Uniformity Matters

 

Whether a cleanroom airflow is unidirectional, non-unidirectional, or mixed, having a uniform cleanroom airflow pattern matters. Cleanrooms are meant to be controlled environments where all systems should work to prevent areas where buildup of contaminants can occur — via dead zones or turbulence. 

 

What is Turbulent Air?

 

Turbulent air, or chaotic air, in a cleanroom is a serious threat to cleanliness. Turbulent air occurs when the airflow pattern is not uniform.

Think of a current moving through water. If the flow was uniform, all of the water would move steadily at the same speed. Obstructions or varying speeds, like rocks or rapids, impede the uniformity of the flowing water. Similarly, when you sweep your hand through water and see eddies and whirlpools form to the side of the current, that’s turbulence. 

Eddies in water may be harmless, but turbulence in cleanroom airflow can cause the uncontrolled movement of contaminating particles — or dead zones where no air is moving at all, where contaminants can build up and threaten sensitive processes in the cleanroom.

 

What Causes Turbulent Air in Cleanrooms? 

 

Turbulence in cleanroom airflow can be caused by non-uniform speeds of air entering the room or obstructions in the path of incoming or outgoing air. Airflow uniformity is about preventing unnecessary turbulent air so the cleanroom can perform at peak efficiency.

 

Minimizing Turbulence in Cleanrooms

 

You can minimize turbulence by designing the cleanroom airflow pattern to work with your layout, equipment, furniture, and personnel. The cleanroom should be removing air at the same or similar speed as it enters. This gives air a clear path to flow to prevent turbulence and dead zones.

Obstructions can also cause turbulent air, so make sure that no large furniture or equipment is blocking fan filter units or exhaust. Adjust equipment with aerodynamic attachments or design features to facilitate airflow, use perforated cleanroom tables to allow air to pass through uninhibited, or modify behavior of personnel to not block or impede airflow within critical zones.

Minimizing Turbulence in Cleanrooms

 

Cleanroom Airflow and Pressurization

 

Another way to minimize contamination using a uniform airflow pattern to establish positive or negative air pressure. Cleanroom pressurization creates a natural barrier to protect or isolate cleaner or less clean zones, respectively. Using negative and positive pressure can be especially useful for sensitive applications such as the manufacturing of healthcare products, medical research, microelectronics, and more.

 

Custom Cleanroom Airflow Design

 

Cleanroom airflow patterns should be designed to work with each unique cleanroom layout and all the furniture, systems, and personnel in the cleanroom for optimal cleanliness during operation. 

A cleanroom engineer uses computational fluid dynamics to map out the cleanroom and place fan filter units and outlets appropriately to meet your classification requirements. This system allows the designer to visualize the pattern of air and make adjustments for cleanroom systems, equipment, and personnel in order to achieve uniformity. It also allows you to anticipate your energy requirements and make your facility as efficient as possible. 

As your ISO cleanroom classification gets lower, having an expertly designed airflow pattern becomes more and more crucial. Work with an expert to make sure your cleanroom airflow is as uniform as possible for your application.

 

Trust the Angstrom Technology Cleanroom Airflow Design Experts

Designing your cleanroom and need a little help establishing an efficient, uniform airflow pattern? Call the experts at Angstrom Technology. From cleanroom airflow design to HVAC and filtration maintenance, we can help you make the best choices for your budget and your classification. 

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