Static electricity is a natural phenomenon familiar in our daily lives, often experienced as a “snap” when removing a sweater or opening a door. However, in manufacturing settings, it can cause issues such as the production of defective goods and injuries due to electric shocks.
Static electricity countermeasures have become essential in manufacturing processes, from plastic molding to semiconductor assembly. By installing anti-static flooring materials, it’s possible to implement static electricity countermeasures throughout an entire factory.
Let’s explain the flooring work involved in implementing static electricity countermeasures for the entire factory, as well as the flooring materials and construction methods used. We mainly explain the following points as a purchasing guide for anti-static flooring materials.
What is Anti-Static Flooring? | Electrostatic Discharge (ESD) Control Flooring Materials
In managing static electricity, floor electrostatic charge within the ESD control area is a major factor due to the static electricity generated by moving people and equipment. There are two main approaches to controlling static electricity on floors: first, the concept of “charging prevention”, which controls the charging through contact with workers, and second, the concept of “grounding”, which allows the generated charge to be discharged gently.
The former is about the idea of preventing charging, while the latter has a strong implication of grounding. However, when managing ESD for floors, it is necessary to be careful because if the footwear within the designated area is not simultaneously decided upon when creating regulations or designing standard documents, the overall management can collapse.
Unlike cleanrooms, the boundaries of ESD control areas are often unclear, and in the past, it was common for people to enter from general areas in their regular footwear. However, with the establishment of ESD management standards by organizations such as IEC and EIA, more companies are marking boundaries and signage.
As a result, it seems that there are fewer instances of workers wearing insulating soles carelessly approaching ESD-sensitive devices (ESDS).
Purpose of Anti-Static Flooring Materials
To prevent the floor from becoming charged
Materials like carpets that are insulators can cause the floor itself to become charged.
To discharge accumulated electric charges from workers who have become statically charged.
If the floor cannot dissipate the charge, the human body will remain charged even if wearing anti-static shoes.
Features of Anti-Static Flooring Materials
When static electricity is generated, it quickly escapes to the earth line. The required electrical resistance value “Ω” (ohms) for conductive mats is between 10^5 Ω and 10^9 Ω; the higher the resistance value, the harder it is for the current to flow.
Structure of Anti-Static Flooring Materials
The structure usually consists of two or more layers, made up of a high-resistance part (green) and a low-resistance part (black).
Static electricity accumulated in the high-resistance part flows to the low-resistance part. Then, it is discharged through the floor or EBP (Ground Bonding Points).
Installation Methods of Anti-Static Flooring Materials
- Clean the floor surface; any residue from tape or oil stains will reduce the adhesive strength of the tape.
- Apply conductive double-sided tape to the underside of the mat and attach it to the floor.
- Use a conductive color mat earthing plate to electrically connect each cut mat.
- Install an earth wire underneath the conductive color mat.
Floor Material Grades Used in Anti-Static Flooring Construction
For anti-static flooring construction, various grades of flooring materials are used, such as conductive grades and static dissipative grades. Both have the characteristic of not accumulating static electricity, but when carrying out flooring work, it is necessary to select the appropriate type according to the application.
Conductive Grade
The property of allowing electrical current to pass through is known as “conductivity.” Conductive grades use conductive resins and have the characteristic of slowly discharging electricity to the ground. They are ideal for locations that require protection against electrostatic interference.
Examples of Applications for Conductive Grades:
- Semiconductor and electronic equipment assembly factories
- Cleanrooms in pharmaceutical plants
- Hospitals and aseptic rooms
Static Dissipative Grade
The term “charging” refers to the state in which a material holds an electrical charge, which can lead to the accumulation of static electricity. Static dissipative grades prevent charging and, thus, the buildup of static electricity.
Examples of Applications for Static Dissipative Grades:
- Electronic equipment assembly factories
- Computer rooms
- Data centers for banks
- Offices
What Is the Difference Between Conductive and Static Dissipative Grades?
The difference between conductive and static dissipative grades lies in their resistance values. When comparing vinyl flooring, conductive grades like CD (Conductive) and CDR (Conductive Rubber) have resistance values between 10^6 and 10^7 ohms. In contrast, static dissipative grades like LS (Lonstat) and LSR (Lonstat Rubber) have resistance values around 10^8 ohms.
The higher the electrical resistance value, the more likely it is for static electricity to generate and accumulate, creating an environment prone to static charge. Therefore, if the goal is to select flooring material that minimizes the generation of static electricity, conductive grades are recommended.
Types of Anti-Static Flooring Materials | Static Electricity Elimination Floor Sheets
There are various types of anti-static flooring materials, and depending on how they are classified, there can be dozens of types. In ESD (Electrostatic Discharge) management, classification is not only based on characteristics but also on material, lifespan, etc. Compared to other ESD control products, it seems more common to classify based on material, composition, and lifespan rather than ESD control characteristics such as surface resistance, volume resistance, and triboelectric charging.
Here, we will explain the classification of floors into two types: ① permanent and ② temporary solutions.
Permanent Anti-Static Flooring Materials | Static Electricity Elimination Floor Tiles
This generally refers to all the common types, but in the context of ESD, this includes consideration of wear, weight, aging, and so-called physical changes as well as chemical durability.
Therefore, the most common materials include rubber or vinyl tiles and sheets, high-pressure laminate materials, powder-flow materials such as epoxy, and other polymer materials, conductive paints, etc. These materials are often seamless in their material and structure, allowing for water drainage, and are quite effective in high humidity environments where the difference in humidity between indoor and outdoor can be problematic.
Among the synthetic resin products, there are some that contain materials that could potentially be problematic when disposed of in the future, which is an important consideration in design and is expected to become a future issue. In terms of force-pet, aside from some office use, its benefits are limited and it is not widely used in production processes.
Temporary Anti-Static Flooring Materials | Charge Prevention Conductive Coatings
In the early ’80s, floor finishers and general antistatic agents were used on P-tiles and normal epoxy floors, but there were problems such as the floor becoming slippery and the coatings being easily removed by water or chemical solvents. These issues have been improved in recent years, and traditional materials have become less common. In fact, the antistatic materials currently used for floor finishes are similar to paints or powder-flowers in forming a similar surface layer.
Those classified as floor finishers are used like general waxes and have grown in the market along with the spread of general building maintenance.
Initially, some of these could easily lose their effect with water or alcohol, but dedicated treatment agents have been developed since the ’80s. Among these, some formed a very strong hardened coating on the floor surface, but due to the potential for inducing contamination of conductivity or antistatic properties, there has been a shift towards products that take into account peeling and wear.
Generally, floor materials can greatly change their characteristics due to the installation process, so ESD management cannot be considered complete just by selecting the right material. Monitoring using indicators such as resistance is necessary at all times, including during and after installation. Additionally, the same precautions that apply to the procurement of general flooring materials, such as safety, non-ESD physical properties, and costs, are needless to say necessary.
How to Choose and Use Anti-Static Flooring?
Next, we will discuss anti-static measures for main flooring materials such as carpets, floor mats, and tiles. The table below compares anti-static flooring materials and their structural characteristics and advantages.
Anti-Static Carpet
Carpets are used in computer rooms and such for their beauty and comfort, but they do not have an anti-static effect for strict environments like IC manufacturing.
Anti-Static Floor Mat
Suitable for localized anti-static management. It is mainly used around workbenches and in inspection rooms where anti-static flooring materials have not been applied. The materials include rubber containing conductive carbon, vinyl, polyolefin, and a two-layer structure of nitrile polymers. Although relatively easy to install, mats can have disadvantages such as getting dirty, material deterioration, and a tendency to curl up.
Anti-Static Coating Floor | Urethane Resin Coating
There are three types of anti-static coating floors: conductive coatings, coating-type anti-static agents, and floor coating-type anti-static agents.
Conductive coatings, mixed with conductive carbon fibers or metal fibers, are very user-friendly and have good anti-static properties, making them suitable for wide factory-wide anti-static applications. However, they are not suitable for clean rooms due to dust generation and durability issues. Coating-type anti-static agents are not originally intended for floors and have issues with durability and re-treatment life (life). The advantage is that they are inexpensive.
Floor coating-type anti-static agents mainly involve a three-liquid process that cleans the floor surface after removing waxes and other coatings and then applies an anti-static agent. While the initial cost is relatively low and the characteristics are good, there are products whose performance maintenance depends on humidity and external factors, and the cost of re-treatment by contractors may be higher than expected.
Anti-Static Laid Flooring Materials
Anti-static laid flooring materials include tiles and sheet types of conductive vinyl materials, as well as carpet types mixed with metal fiber fibers. Tiles and sheet types have good anti-static properties and durability due to the conductive materials distributed throughout the tile, making them suitable for static electricity management. However, the cost can be very high.