Is ULPA mandatory for ISO Level 5 projects?

When selecting filters for ISO Class 5 projects, there is often a default judgment: ULPA must be used for Class 100 filters. This statement is not accurate. ISO 5 describes the air particle concentration in a specified area, specified particle size and occupancy state. It does not directly specify a certain filter material or efficiency level. Whether to use ULPA depends on process-sensitive particle size, background load, equipment structure, system resistance and verification requirements.

If ULPA is specified only by grade name, two problems may occur: the sensitive particle size of the product does not require such a high grade, but the fan cannot move due to increased resistance; or the tiny particles that really need to be controlled at key locations are not individually identified, and upgrading the filter alone does not solve the problem. The following begins with the steps of classification definition, process requirements, system matching, and on-site verification.

ISO classification is not a list of filter models

ISO air cleanliness classification describes the particle concentration in an area and does not directly correspond to a certain filter model. For the same ISO 5 level, different filtering solutions may be used in different projects. The reason is:

• Process sensitive particle sizes are different;

• Background air loads vary;

• Equipment structures and airflow paths are different;

• Allows for varying particle levels and detection capabilities;

• System resistance and fan margin are different.

If you are still unclear about the difference between space rating and filter efficiency, you can read What is the difference between cleanliness level and filtration efficiency? First, distinguish these two concepts. The cleanliness level must also indicate the measured particle size. For specific reasons, please refer to Why must the particle size be indicated in the cleanliness grade?。

First confirm the process sensitive particle size

Whether to use ULPA, the first step is to confirm which particle size the product is most sensitive to. When ISO 5 is compared based on the concentration of particles not less than 0.5μm, it may be achieved with a suitable HEPA solution combined with sealing and airflow; but if the process is sensitive to smaller particles or has special surface requirements, the control indicators need to be listed separately before determining whether ULPA is required.

For specific judgment, please refer to How do HEPA and ULPA match cleanliness goals? , first confirm the sensitive particle size and allowable level, and then fall to the specific grade. To choose between H13, H14 and U15, please refer to How to choose between H13, H14 and U15? , the efficiency requirements and resistance conditions of the three levels are different.

Address upgrade needs to specific risks

If critical processes are indeed more sensitive to tiny particles, additional control indicators and detection capabilities should be confirmed, and HEPA and ULPA configurations should be compared. You cannot judge based on industry names or habits alone, nor can you omit installation leakage verification.

Things that need to be confirmed include:

• The level of particles allowed on the product surface;

• Whether the detection instrument can cover the target particle size;

• Whether the test particle size in the filter efficiency report corresponds;

• Whether the background load is stable;

• Are there any sources of dust inside the equipment?

How to read the filter efficiency report can be found in How to read the test particle size in the filter efficiency report? , to avoid direct comparison of data of different calibers.

Background load and equipment structure impact plan

For the same ISO 5 level, the background load is different, and the filtering scheme may be different. If the background air particle concentration is high, or there is ongoing dust production inside the equipment, a higher efficiency filter or a more complete seal may be needed; if the background load is low and the product exposure time is short, a suitable HEPA solution may also meet the requirements.

Device architecture also affects filtering choices. The airflow path, opening position and exhaust relationship in the closed equipment cavity are different, and ULPA is not the only solution. For details, please refer to How to plan clean air supply for closed equipment cavities? , first confirm the protection boundary and air flow path, and then determine the filtration level.

Check the working point of the whole machine after replacing ULPA

Higher efficiency filters tend to have higher resistance. After switching to ULPA, if the fan operating point remains unchanged, the actual air volume may decrease, resulting in insufficient terminal wind speed. At this time, even if the efficiency of the filter material is improved, the workstation protection may become worse.

When selecting, you should check:

• ULPA’s initial resistance and final resistance at the target air volume;

• The working point of the fan under corresponding resistance;

• Whether the input power and noise of the whole machine are still within the allowable range;

• Whether the installation space and maintenance conditions match.

Please refer to the working point reading method Why should we look at the complete performance curve when selecting FFU? , the test configuration of nominal air volume can refer to Is FFU's nominal air volume tested with a filter? . If the filter area is insufficient, the fan may require higher pressure to maintain flow. For details, please refer to How does insufficient filter area affect fan selection?。

Sealing and installation leak detection cannot be omitted

If the high-efficiency filter is not properly installed and sealed, bypass leakage will allow unfiltered air to enter the clean side. At this time, upgrading ULPA cannot achieve the expected results. After installation, the frame seal, installation interface and leak detection conditions should be checked.

If there are abnormal particles on site but the filter efficiency is acceptable, priority should be given to checking the sealed bypass and airflow short circuit. Can be referenced Does higher filtration efficiency necessarily lead to improved site ratings? and What particle problems can airflow short circuits cause?。

Initial resistance and final resistance are used for different judgments

The initial resistance of ULPA is usually higher than that of HEPA of the same size, and the final resistance should also be judged based on project requirements. The final resistance is not the only life criterion. Damage, moisture, process risks and actual air supply capacity must also be considered. For details, please refer to What are the initial resistance and final resistance used to judge?。

On-site verification is the final judgment

Regardless of whether you choose HEPA or ULPA, it must ultimately be confirmed through on-site verification. Verification should include:

• Filter installation, sealing and leak detection;

• Wind speed and airflow direction at key locations;

• Particle detection with specified particle size and sampling location;

• Dynamic verification under actual operating conditions;

• Exception recovery time records.

The sampling point layout should cover the actual product exposure location, rather than just under the air supply outlet. Related methods can be found in Why can’t the sampling point be located just below the air supply outlet?。

Scenario judgment: different project plans may be different

ISO 5 is also written in the ordinary background area and inside the precision equipment, but the process-sensitive particle sizes are different, and the filter selection may be different, and the technical conditions should be formed separately.

The wafer exposure point inside a certain equipment is sensitive to tiny particles, so ULPA is used and the fan working point is checked; the background room uses H14 with sealing and airflow organization to meet ISO 5 requirements. The two areas are verified separately and do not apply to each other.

Another project was directly configured according to the '100-level ULPA' unified configuration, and the terminal wind speed dropped after installation. Adjustment method: retain ULPA in key areas and increase fan capacity, and use H14 in background areas. After adjustment, the system resistance is controllable and the key areas meet the requirements.

These two situations illustrate that whether to use ULPA for ISO Level 5 projects must be comprehensively judged based on process particle size, background load, system resistance and verification requirements.

Key points for selection and acceptance inspection

Aili industrial equipment supporting support

Whether an ISO Level 5 project should be admitted to ULPA should not just look at the level name. Aili Industrial also handles air filters, fans, motors, control systems and complete machine assembly. It can check the process-sensitive particle size, background load, filter efficiency, initial and final resistance, and complete machine working points in the same configuration to help determine whether HEPA sealing and airflow organization are sufficient, or whether it is necessary to partially adopt ULPA and adjust the fan capacity accordingly. Specific filter parameters can be viewed HEPA and ULPA filters , the complete machine package can be viewed FFU clean air supply products and EFU equipment side fan filter unit。