Cleanrooms are among the most controlled environments in the world. These facilities follow strict protocols to control airborne particles, microbial contaminants, and electrostatic buildup, which can compromise sensitive manufacturing processes.
Among these, electrostatic buildup is a particularly serious concern because it can lead to Electrostatic Discharge (ESD), a phenomenon capable of damaging delicate electronic components and precision instruments.
Even an ESD of as low as 10 to 20 volts has the potential to damage delicate electronic components and compromise precision instruments. Humans can only perceive ESD when it reaches 3,000 volts, making these damaging discharges virtually undetectable.
Cleanrooms manufacture semiconductors, circuit boards, aerospace sensors and control systems, satellite components, and other expensive high-precision equipment. This is why organizations follow cleanroom ESD requirements meticulously; ESD-related failures could result in the loss of millions of dollars and safety hazards that can have devastating consequences.
Here’s everything you need to know about ESD, including protection requirements, ESD standards, and control measures.
What Is Electrostatic Discharge?
Electrostatic Discharge (ESD) is the sudden and momentary transfer of electric current between two electrically charged objects. It’s the static shock you experience after walking across a carpet or touching a metal doorknob after removing a wool sweater.
Small electrostatic discharges don’t usually cause harm to humans and typically require around 3,000 to 5,000 volts to even be felt. The same can’t be said for electrical and industrial components, which can get damaged by discharges as low as 10 to 20 volts.
The consequences of ESD damage can be quite significant.
In cleanrooms, a minor ESD event can ruin multi-million dollar equipment like semiconductors and photolithography masks. Large-scale ESD failures are even more disastrous, with some igniting fuel vapors in surrounding areas and others compromising critical control systems in aerospace, manufacturing, and energy production.
ESD control procedures prevent these potentially disastrous events by reducing the risk of equipment malfunctions, product damage, and operational failures.
What Causes Electrostatic Discharge?
Electrostatic Discharge is caused by tribocharging (friction) and electrostatic induction (charge redistribution due to a nearby electric field).
Normally, objects contain an equal number of electrons and protons.
Tribocharging occurs when objects with different electrical potentials (one more positively charged and the other more negatively charged) come in contact and then separate, creating a buildup of static electricity.
The static electricity discharges rapidly, releasing concentrated energy that can be damaging to sensitive electronic components.
Electrostatic induction, on the other hand, occurs when a charged object is brought near a neutral conductor, causing the charges in the conductor to rearrange. No physical contact is needed—the effect happens because of the electric field of the charged object.
At a micro-level, an ESD is nothing more than a tiny electric arc or spark that is oftentimes invisible to the eye. Micro-level ESD discharges electricity as low as 10 volts. For reference, humans perceive ESD only when they reach 3,000 volts and feel it at 5,000 volts.
Conversely, large-scale ESD events involve thousands to millions of volts and can potentially result in explosions.
Here’s a table comparing the voltage levels of various ESD events:
| ESD Event | Voltage Level | Result |
| Micro-ESD (Small-scale) | < 100 volts | Can damage sensitive electronics but is undetectable to humans. |
| Typical Human ESD | 3,000 volts to 10,000 volts | Felt like a small shock when touching an ESD-prone material (i.e., a metal doorknob). |
| Industrial ESD Events | >10,000 volts | Can damage electronic components in factories or cleanrooms. |
| Large-Scale ESD | 100 million to 1 billion volts | Capable of massive destruction, like explosions |
ESD Cleanroom – Why is ESD Control Important?
A cleanroom is a controlled environment free of pollutants and airborne microbes like dust, pollen, and other contaminants. This environment is often used for research or the manufacture of highly sensitive electrical components, like rechargeable batteries, semiconductors, and pharmaceutical products.
ESD Control is a set of guidelines and procedures that eliminate the build-up of static electricity when working on ESD-sensitive equipment.
Since cleanrooms often manufacture expensive and potentially dangerous parts, strict ESD control measures are necessary to prevent costly damage and safety hazards.
Even a minor electrostatic discharge of 10 to 50 volts—300 times lower than the amount a human can perceive—can compromise the functionality of electronic equipment. These devices are extremely sensitive and need to be manufactured in a highly controlled environment like cleanrooms to ensure product reliability and functionality.
ESD Environment & Humidity Control
Higher humidity levels are a key component of ESD control.
Low humidity increases the susceptibility of static build-up in materials like plastic, synthetic fibers, and other insulative surfaces due to reduced surface conductivity (also known as decreased surface resistivity).
To mitigate this risk, cleanrooms use climate-controlled HVAC systems with real-time monitoring to maintain relative humidity levels of between 40% and 60%.
The moisture content in the air creates a vaguely conductive film over an insulating surface, greatly reducing the risk of a sudden ESD.
For reference, air-conditioned offices and homes usually maintain humidity around 30% to 50% for comfort. At 40% humidity, the air feels dry but not uncomfortably so. At 60%, it feels more humid, but not in a muggy or oppressive way. In other words, it’s a decently comfortable environment to work in.
This isn’t to say that moisture outright prevents ESD; it just absorbs it better. What happens is that instead of releasing the static in the surrounding air, it’s released to the water in the air. ESD still occurs but is spread across multiple water droplets or molecules rather than being concentrated in one place.
ESD Requirements for Cleanrooms
Alongside humidity control, cleanrooms have several other ESD requirements to minimize static buildup and discharge. Below is a breakdown of ESD protection measures and standards.
Electrostatic Discharge Protection Measures
Cleanrooms implement a combination of environmental control, grounding systems, and ESD-safe materials to prevent ESD-related damage. These include:
Proper Handling Techniques
Employees are trained to follow strict ESD handling controls, such as avoiding rapid movements that generate static and making sure sensitive materials are transported in ESD-safe packaging.
Actions like walking around or repairing certain equipment naturally generate several thousand volts of electrostatic charge on the human body, which is why employees must be mindful of their movements.
The same is said with mobile equipment like carts, trolleys, or other wheeled items as they can transfer the static created to the products being transported on the equipment.
Employees are often asked to plan activities far in advance and limit how often they enter and exit the cleanroom. They’re also trained to minimize direct contact with surfaces and tools when using electro-sensitive equipment like forceps or tweezers.
Use of Designated Entryways
Employees are required to enter and exit through specific doors to maintain controlled airflow and reduce contamination risks. These entryways often include airlocks, gowning rooms, and pass-through chambers that limit static buildup and airborne particles.
Implementation of Ionization Technology
Cleanrooms often use ionization technology to control electrostatic discharge and minimize particle contamination.
Ionization technology introduces positive and negative ions in the air that neutralize static electricity. These particles either attract or repel charges, effectively preventing the buildup of electrostatic energy on surfaces, equipment, and personnel.
Remember that static electricity often results from an imbalance of positive and negative charges. Ionization neutralizes these charges by introducing an equal number of positive and negative ions, balancing the charge.
Alternating Current (AC) ionizers, steady-state Direct Current (DC) ionizers, and pulsed DC ionizers are common technologies used for static control and are typically implemented through air blowers, ionizing bars, and overhead ionizers.
Electrostatic Discharge Standards
Cleanrooms are expected to follow a number of ESD standards to ensure compliance with industry regulations. Other than equipment failures, product defects, and costly recalls, non-compliance may result in fines, legal liabilities, and damage to a company’s reputation.
The ESD Association has published a lengthy article containing all these standards which you can read on the official website. They fall into several categories, including those that provide guidance or controlled factory environments, procedures like grounding and packaging, and standardized test methods to evaluate the materials used in ESD environments.
Here are some of the most widely recognized ESD standards:
- ANSI/ESD S20.20: Defines ESD control program requirements for protecting electronic components.
- IEC 61340-5-1: Outlines ESD protection measures for manufacturing and handling sensitive devices.
- MIL-STD-1686: Lists ESD control methods for defense and aerospace applications, typically for military use.
- JEDEC JESD625: ESD-safe handling procedures for industries that produce semiconductors.
- DIN EN 61340-5-1: European standard that outlines requirements for managing electrostatic charges industries where sensitive components are handled, like cleanrooms.
- NASA-STD-8739.7: Specifies ESD control requirements in NASA environments.
ESD Control Measures & Equipment
ESD-controlled environments use specialized equipment to minimize static build-up. This primarily comes in the form of ESD-safe flooring, ESD-safe clothing, and ESD-safe tools.
Electrostatic Discharge Flooring & ESD Grounding
Electrostatic discharge floorings are specifically designed to safely dissipate electric charges to the ground, preventing buildup on equipment and personnel.
ESD flooring must produce less than 100 volts in a standard voltage to be considered ESD safe, according to ANSI/ESD STM97.2.
ESD flooring materials that fall into this category include:
- Conductive vinyl
- Conductive Rubber
- Low KV carpet tile
- ESD Epoxy and Polyurethane
ESD-Safe Mats
ESD-safe mats can include two layers of static dissipative rubber, a 100% nitrile fire-resistant rubber compound, or a conductive layer sandwiched between two dissipative layers. Some mats also feature a single homogenous conductive layer. These mats are used on tabletops, workbenches, and floors to prevent static buildup.
Electrostatic Discharge Wrist Strap
According to the ESD Association, ESD wrist straps are the primary means of grounding personnel. The wrist straps are connected to an ESD-safe ground point (grounded workstation, mat, earth bonding plug, etc.) and safely dissipate static electricity from a person’s body.
ESD-Safe Clothing
Some clothing materials, like those made of synthetic fabrics, generate electrostatic charges that transfer into electro-sensitive equipment.
To mitigate this risk, personnel are required to wear ESD-safe clothing made from anti-static materials like cotton, polypropylene, and polyester with conductive fibers like carbon, metal, or conductive thread.
ESD Gloves and ESD Shoes
Along with ESD clothing, personnel are required to wear ESD gloves and ESD shoes.
ESD gloves are made with nylon, polyester with carbon, nitrile with anti-static coating, or vinyl. Meanwhile, ESD-safe shoes are made with conductive leather and often feature carbon-loaded rubber soles.
ESD-Safe Tools
When handling or working on ESD-sensitive equipment, all electrical tools must feature grounded (3-prong) plugs.
Non-powered hand tools (like pliers and tweezers) are grounded through the ESD work surface and the person working on the item. These tools are commonly made with conductive materials like stainless steel, coated alloys, or titanium.
Conversely, ESD-safe power tools—like electric screwdrivers, soldering irons, and heat guns—are designed with conductive or static-dissipative housings. These tools need to be ESD-certified and properly grounded to avoid accidental electrostatic discharge.
Plastic tools are a big no-go unless they’re specifically designed with anti-static properties.
ESD-Safe Walls
ESD-sensitive facilities often use walls coated with aluminum-based or aluminum honeycomb materials. These specialized coatings contain conductive elements that make the surface static dissipative. Curtains are also made with static dissipative vinyl to minimize and prevent electrostatic buildup.
ESD Control Program & Testing
A well-thought-out ESD control program features seven key steps. These include:
- Research and Compliance Verification
Before implementing an ESD control program, organizations must identify applicable ESD standards and ensure compliance with industry regulations. This step involves evaluating cleanroom requirements, conducting risk assessments, and establishing control measures.
The most reliable resources for research and compliance include:
- ESD Association (ESDA): An international organization that sets the standards, guidelines, and best practices for controlling ESD in various industries and environments. It was established in 1982 and is the key publisher of ANSI/ESD S20.20, which provides a framework for ESD-safe environments.
- IPC Association (IPCA): A global trade organization dedicated to the electronics manufacturing industry, specifically OEM (Original Equipment Manufacturers), PCB (Printed Circuit Board), and EMS (Electronics Manufacturing Services), as well as wire and cable harness manufacturers and suppliers.
- ESD Training Resources: Both ESDA and IPCA provide online courses, in-person workshops, and certification projects on the proper use of ESD-safe tools and equipment, ESD fundamentals and prevention techniques, and compliance with ESD standards. You can find these resources on their respective websites.
- ESD Product Manufacturers (Desco Industries, SCS, 3M, Simco-Ion, etc.): ESD product manufacturers are valuable sources of information on ESD compliance and best practices. However, organizations must double or even triple-check the source material because some product manufacturers can be biased.
- Identify ESD-Sensitive Work Areas
All ESD-sensitive work areas must be properly identified and labeled. Engineering and testing areas, assembly and packaging stations, laboratories, and areas that handle unshielded products or components fall into this category.
- Select a Grounding or Equipotential Bonding System
ANSI/ESD S20.20-2014 section 8.1 states the following: “ESDS items, personnel, and any other conductors that come into contact with ESDS items must use grounding/equipotential bonding systems that are at the same electrical potential.”
This can be achieved via an equipment grounding conductor, an auxiliary ground, or equipotential bonding.
Equipment grounding conductors are dedicated electrical paths that safely direct unwanted static charges away from ESD-sensitive devices. It connects all conductive items, including workstations, flooring, and personnel grounding devices, to a common electrical ground.
Meanwhile, an auxiliary ground acts as a secondary grounding system that provides an independent path for electrostatic discharge, separate from the main electrical ground.
If a ground facility isn’t available, ESD protection can be achieved through equipotential bonding, which connects conductive objects with a protective bonding conductor.
- Determine the Grounding Method for Personnel
Organizations must provide employees with grounding methods to reduce the risk of electrical discharge. Two common grounding methods include a wrist strap and a flooring system.
Wrist straps must be worn whenever seated personnel work on electro-sensitive equipment and products. Standing or mobile workers, on the other hand, require ESD footwear such as heel straps or ESD-safe shoes to maintain a neutral electrical charge.
- Develop a Plan for Tasks, Activities, and Procedures
Personnel who work in ESD-sensitive environments must follow a set of guidelines and procedures to ensure electrostatic discharge is controlled and minimized at all times.
Ideally, employees must undergo extensive ESD awareness training and understand proper handling procedures before working on sensitive components.
- Invest in Proper Environmental Controls
Environmental controls, such as a climate-controlled HVAC system with real-time monitoring and various ionization technologies, are a must in an ESD-sensitive environment. Cleanrooms and similar facilities must maintain humidity levels between 40% and 60% to reduce electrostatic buildup.
- Regular Maintenance and Testing
ESD devices like wrist straps, heel straps, and grounding equipment tend to lose their effectiveness over time, so regular testing and calibration are essential to maintain their reliability.
One of the most reliable ways to test the functionality of ESD equipment is to use a static charge meter.
ESD equipment and surfaces must display a static charge of less than 100 volts, depending on the sensitivity and size of the product. We’ll go more into detail about ESD testing in the upcoming sections.
It’s likewise a good idea to invest in anti-static vacuum cleaners, which minimizes the chance of damaging ESD-prone equipment like radars, GPS units, computers, file servers, and copiers.
Anti-static vacuums feature conductive/dissipative hoses, allowing them to neutralize electrostatic charges when the power cord is properly grounded through an electrical outlet ground prong.
What Does “ESD Safe” Mean?
ESD safe is a product or material designed to minimize or prevent electrostatic discharge. These products meet the requirements and industry standards noted in ANSI/ESD S-20.20-2014, which include:
- Grounding with a low resistance of under 2 ohms between the tip and ground.
- Maintaining a voltage difference of no more than 2 millivolts between the tip and ground.
- Being made from ESD-safe materials with a surface resistivity below 10¹¹ ohms/square and passing standard static decay tests.
ESD Testing
ESD Testing verifies a product’s ability to withstand or protect itself against electrostatic discharge. It involves subjecting the equipment under test (EUT) to controlled ESD events, typically simulating real-world static electricity scenarios.
In other words, it measures how well an item dissipates static charge, how much voltage it can withstand, and whether it generates static electricity itself.
ESD tests are divided into device-level tests and system-level tests.
Device-level tests include ESD immunity tests on a machine model (MM), a human body (HBM), and a charged device model (CDM).
On the other hand, system-level tests ensure that the equipment doesn’t get damaged or destroyed by ESD that occurs in daily life (like when a strike occurs when the device is plugged into a USB port).
These tests typically target the device’s touch sensors, connectors, and antennas.