How to configure ULPA for static-sensitive equipment?

Static-sensitive devices—semiconductors, precision electronics, sensor packaging, optical devices—have strict control requirements for electrostatic discharge (ESD). When configuring ULPA, many people will ask in passing: Is this filter anti-static?

The premise of this problem needs to be clarified first. ULPA's job is to control particles, not static electricity. It does not actively generate static electricity by itself, nor can it replace the equipment's grounding system and electrostatic protection design. However, in actual operation, frictional charging may occur when the air flows through the filter material. If the filter material and structural materials are insulated, charges may accumulate. Whether these charges will affect downstream sensitive devices depends on the overall electrostatic protection system of the equipment.

Therefore, when configuring ULPA, the answer is not 'Can this filter be anti-static?', but: In the electrostatic protection system of this equipment, will the material and structure of the filter become a problem and whether special treatment is required.

First separate the static control and filtration control

This is the starting point for configuration.

Filtration control focuses on particle penetration rate, sealing integrity, and air volume resistance. The goal is to make the particle concentration in the supply air meet the process requirements.

Static control focuses on charge generation, accumulation, and discharge pathways. The goal is to avoid electrostatic discharge from damaging sensitive components or attracting particles.

The evaluation standards, testing methods, and responsible departments of the two are different. The efficiency rating of a filter and the level of electrostatic protection are not the same thing. A U16 rated product may fully meet particle control requirements but require additional grounding or material handling in the static control system. On the other hand, the filtration efficiency of a product with anti-static design may not necessarily meet the process requirements. For specific grade selection, please refer to the relevant instructions of U15, U16, and U17.

They must be confirmed separately when configuring and cannot replace each other. Filtration performance is supported by filter data, and electrostatic protection is supported by equipment grounding design and material testing.

Where static electricity may come from

When a ULPA is operating in a system, several locations may generate or accumulate charges.

The air flow rubs against the filter material. When air passes through the filter material, the friction between particles in the airflow and the surface of the filter material may generate charges. The amount of charge depends on the air flow rate, particle concentration and material properties. In low-humidity environments, this frictional charge is more likely to accumulate.

Insulating material surface. If insulating materials are used in the filter media, sealing gasket or outer frame, the generated charge may not be discharged through the material itself, but will accumulate on the surface. After accumulation to a certain extent, it may be released through discharge.

Install structural isolation. If there is no conductive connection between the filter element and the equipment frame, the charge may not be discharged to the equipment grounding system, even if the metal frame itself is conductive.

Maintenance operations are introduced. When replacing the filter element, the operator, tools or packaging materials may be electrostatically charged. If the filter element is not adequately connected to the grounding system, these charges may be introduced into the system. Device-side applications such as The EFU equipment-end fan filter unit has a compact internal space, and the contact state between the filter element and surrounding structures requires more attention during installation and replacement.

How to match materials and structures

The core idea of ​​​​static control is: either reduce the generation of charge, or allow the generated charge to have a controllable discharge path.

Reduce charge generation. Choosing materials with a low propensity for air flow friction to charge can reduce charge generation at the source. However, this effect is greatly affected by working conditions and is difficult to completely eliminate.

Provide a drain path. It is more reliable to have the conductive parts of the filter connected to the equipment grounding system. If the outer frame is made of metal and has a reliable electrical connection with the installation frame, the charge can be discharged through the outer frame to the device ground. If the outer frame is made of insulating material, or the connection path is discontinuous, this relief path will not be established.

Ground continuity must be confirmed, not just whether there is a ground wire. The contact surface between the outer frame and the mounting frame, the conductivity of the fasteners, and whether there is an insulating coating or gasket blocking the path will all affect the grounding effect. After installation, it is recommended to measure the connection resistance at key points to confirm that the leakage path is effective. For specific frame material selection, please refer to the relevant instructions on the comparison between aluminum alloy and stainless steel.

Material matching should be considered as a whole. The filter media, gasket, outer frame and mounting structure each have different conductivities. By treating only one component, a complete relief path may not be created. For specific configuration plans, please refer to HEPA/ULPA air filters . Product information for

What information should be confirmed when configuring

If the equipment has clear electrostatic protection requirements, it is recommended to provide the following information to the supplier when configuring ULPA.

Static control objectives. Is it to control surface resistance, volume resistance or discharge voltage? Different indicators correspond to different materials and testing methods.

Grounding method. How are equipment racks grounded? Which parts of the filter element need to be connected to the grounding system? Where are the connection points?

environmental conditions. What is the humidity range? Low humidity environments have a more obvious impact on static electricity accumulation. Temperature, air velocity, and particle concentration also need to be specified.

Test methods. If the project requires electrostatic testing of the filter or installation status, the test standards, measuring points, and judgment conditions need to be clarified.

Filtration performance requirements. While meeting the requirements for static electricity control, filtration indicators such as efficiency level, air volume, resistance, and sealing method must also be explained. The two cannot be substituted for each other. involving The selection of ULPA ultra-high efficiency filter can be checked in conjunction with the overall protection requirements of the equipment.

Verify that it covers both filtration and electrostatic dimensions

After the configuration is completed, the verification must be divided into two lines.

Filter side verification. Conduct on-site leak detection according to project requirements to confirm sealing integrity; measure air volume and surface wind speed to confirm air supply conditions; conduct regional particle testing as needed. This part is the same as the regular ULPA project. For the specific acceptance sequence, please refer to the relevant instructions on whether to adjust the air volume first or check for leaks first.

Static side verification. According to the requirements of the equipment's electrostatic protection system, check the connection status of the filter element and the grounding system to confirm that the discharge path is effective. If necessary, measure resistance or discharge voltage at critical points. This part is usually performed by the equipment party or ESD specialist, and the filter supplier provides material and structural information support.

The two sets of records are kept separately. The filter leak detection records and electrostatic test records correspond to their respective product numbers and installation locations. During subsequent maintenance or troubleshooting, they can be traced separately. Supporting FFU fan filter unit system, unit parameters and filter element data must also be recorded.

What to pay attention to during maintenance

Static electricity control is ongoing and maintenance operations must also be managed.

Verify the ground connection when replacing the filter element. After the new filter element is installed, not only confirm that it is installed in place and sealed, but also confirm that the grounding path has been restored. During disassembly and assembly, connections may be loosened or insulation may be introduced.

Check material aging. After aging of gaskets, colloids or surface treatments, material properties may change, affecting grounding continuity or electrification tendencies. Check regularly during the replacement cycle. For specific colloid inspection methods, please refer to the relevant instructions for sealants.

Document maintenance changes. If the filter element is replaced with a different model, the installation structure is adjusted, or the seal is replaced, the impact on static control needs to be evaluated. It cannot be assumed that 'passed filtering means qualified electrostatic protection'.

Project judgment example

A certain precision electronic equipment project requires ULPA filters inside the equipment and has clear requirements for electrostatic protection.

The preliminary plan uses conventional ULPA and a metal frame, which should be fixed in the normal way during installation. During the ESD test of the equipment, it was found that the surface potential of a certain measuring point was relatively high. The investigation found that an insulating gasket was used between the outer frame of the filter element and the installation frame, and the grounding path was discontinuous.

Adjustment method: Replace with a conductive sealing gasket, confirm that there is a reliable electrical connection between the outer frame and the installation frame, and measure the connection resistance after installation. There is no change in filtration performance, but a static discharge path is established. After the equipment was retested, the surface potential returned to the acceptable range.

The key point in this case is: the metal frame itself does not mean that the grounding is effective. Every link along the connection path—gaskets, coatings, contact surface condition—needs to be verified. involving When selecting HEPA/ULPA air filters , static control requirements should be included in the planning phase and evaluated.

Selection and Acceptance Checklist

About Aili Industrial’s static electricity control package

The core of the ULPA configuration of electrostatic-sensitive equipment is to treat filtration performance and static control separately, and then find a matching solution in terms of materials and structure. These two lines do not cross, but they need to be met at the same time.

Aili Industry has independent manufacturing capabilities in filters, fans, control systems and sheet metal processing, and can provide ULPA ultra high efficiency filter、HEPA high-efficiency filter and supporting air supply equipment. For projects with electrostatic protection requirements, we can assist in checking the filter element outer frame material, seal conductivity, and installation coordination method based on equipment grounding methods, material requirements, and installation conditions. When the filter is matched with equipment such as FFU and EFU, the grounding design of the whole machine and the filter element interface can be confirmed together during the planning stage.

Providing static control objectives, grounding methods, environmental conditions, and filtration requirements when inquiring will help confirm the appropriate configuration plan. The specific selection is subject to the technical documents and test results confirmed by the project.