
20 Aug ESD Control in Cleanrooms: A Simple Guide
Believe it or not, a tiny spark can cost thousands of dollars. In many manufacturing industries, controlling electrostatic discharge (ESD) is an important part of creating quality goods. The most obvious example of this is in semiconductors, where tight controls are necessary in many stages of the manufacturing process. In this article, we’ll guide you through the basics of ESD in cleanrooms, explaining what ESD is, how it causes problems, and finally, how to prevent damage from it.
Please note that this is a simple guide, and we will not dive too deep into the physics of ESD, as it requires an in-depth understanding of electromagnetic theory.
What is Electrostatic Discharge?
Electrostatic discharge is an event that occurs when two oppositely charged objects come into contact or are brought close enough together, causing a sudden release of electricity. Examples of ESD include the shock you feel when touching a metal doorknob after dragging your feet over carpet, the spark that occurs when removing clothes from a dryer, or even lightning. In a cleanroom context, ESD is important because such discharges can damage electric parts, equipment, and also affect the cleanliness of a space.
Why is Electrostatic Discharge an Issue in Cleanrooms?
As we just mentioned, ESD is an important concern in cleanrooms because it can hurt electronic parts and equipment, as well as contribute to overall contamination.
As the size of electrical parts becomes smaller, they require less energy for ESD to cause significant harm. As a result, it is becoming more necessary than ever for cleanrooms to ramp up ESD protection.
Similarly, ESD events can cause malfunctions in cleanroom equipment (such as photolithography masks in semiconductor cleanrooms). A result of all these problems is reduced manufacturing yields, and so cleanroom design must prevent ESD sources as much as possible.
Let’s take a closer look at the ways that ESD can cause problems in cleanrooms.
Impact on Electronic Parts
As we mentioned already, the reduction in the sizes of electronic components means that they are more vulnerable to ESD. Industries like semiconductor fabrication are especially at risk because damages from ESD can occur at extremely low voltages.
Particle Contamination
Strangely enough, ESD events can also cause particulate contamination. For example, when static charges build up and are discharged, particles can be pushed into the air in different directions, which of course reduces control over the environment.
A different yet related concern is the buildup of static electricity in general, which can make it difficult to clean surfaces. Static charge on surfaces makes the removal of sub-micron particles extremely difficult. Without going too far into the physics, electrostatic forces can cause tiny particles to stick tightly to them, which makes them harder to remove/clean.
Equipment Malfunctions
Further, ESD not only affects the manufactured products but also the equipment used to make them. As equipment like photolithography tools and microprocessors become more advanced and operate at higher speeds, they become increasingly vulnerable to ESD-related malfunctions. As you might expect, this can cause major problems and disruptions for businesses, and this only underscores the need for ESD control.
How Do You Control ESD within Cleanrooms?
We’ve already established how ESD and electrostatic forces can be a real problem in some industries. Luckily, there are many methods and tools for mitigating their influence as much as possible. Here are some of the main ways that cleanrooms can combat it.
Conductive and Dissipative Materials
When creating a cleanroom, you need to be mindful of the materials that are used. Though “conductive” and “dissipative” sound like big and complicated words, it is actually quite simple.
Conductive materials prevent static charge buildup by quickly dissipating electricity. All this means is that it gives the forces somewhere else to move to (away from the important parts and equipment). They are often used in floors, work surfaces, and tools.
Dissipative materials cause static charges to drain away slowly, which lowers the risk of sudden discharges. For example, some materials, like certain plastics, can hold onto static charges (which is not ideal). Cleanrooms often use static-dissipative plastics instead.
The important takeaway is that both types of materials reduce the damage caused by ESD.
Grounding Techniques
Grounding is another tool in the box for controlling ESD. It involves connecting people, equipment, and workstations to the ground so that any static electricity created can safely flow away, typically through special flooring (such as static-dissipative materials). Some tools for grounding personnel may include wrist straps, heel straps, and special mats.
Ionization
Furthermore, ionizers are often used when grounding techniques cannot, for whatever reason, be used. What these systems do essentially is neutralize static charges by releasing ions into the air. These ions attach to charged particles (and neutralize them) to prevent ESD events.
ESD-Safe Clothing
Selecting certain types of clothing worn in cleanrooms is yet another measure that can be taken to reduce ESD. Such special gowning is often made from static-dissipative materials, and these fabrics often include continuous threads of conducting material woven into the fabric.
Humidity Control
Finally, cleanrooms may control humidity to reduce static charge buildup. This is a widely used technique because humidity levels directly influence the likelihood of ESD. Without getting needlessly complicated, when humidity is too low (below 40%), static electricity tends to accumulate and cause problems; as a result, within cleanrooms it is often maintained around 40-60%. (At this level, static charges dissipate more easily.)
ESD Control in Cleanrooms: The Bottom Line
Controlling ESD in cleanrooms is necessary in many cleanroom applications, mainly to protect electronics, equipment, and overall cleanliness. A cleanroom that is designed to reduce ESD as much as possible may use conductive and dissipative materials, grounding techniques, ionization systems, ESD-safe clothing, and humidity control. When designing a cleanroom where products are affected by static electricity, it is always important to prioritize ESD control measures.
Are you looking to build a cleanroom designed to lower ESD-related damage as much as possible? Contact the experts at Allied Cleanrooms today to get a free quote on a custom buildout.
FAQs about ESD Control in Cleanrooms
1. Can ESD damage occur even in well-maintained cleanrooms?
Unfortunately, yes. Damage can still occur if controls are not implemented well or maintained. This is why regular audits in cleanrooms are so important to preventing damage.
2. What industries benefit most from ESD control in cleanrooms?
The most obvious example of an industry that benefits from ESD control is the electronics/semiconductor industry. However, there are many others that benefit from it as well, such as aerospace, pharmaceuticals, and medical device manufacturing.
3. How frequently should ESD controls be audited in cleanrooms?
ESD controls should be audited often and regularly, but the frequency will depend on what industry the cleanroom is in and also what regulations it is governed by.
4. What are the main standards governing ESD control in cleanrooms?
ANSI/ESD S20.20 and IEC 61340 are the primary standards that have guidelines for ESD control where electronics are handled, including cleanrooms. These standards cover materials, grounding, ionization, and more.