How to divide the work between device-side EFU and room FFU?

In clean systems, FFU and EFU are often discussed together, but their tasks are different. The room FFU mainly participates in the background environment air supply to maintain the air cleanliness of the room or area; the equipment-side EFU mainly protects the interior of the designated equipment or local operating areas and solves particle control problems in equipment cavities, workstations or critical paths.

The two can be used synergistically, but cannot replace each other. If the room FFU is used as the internal protection of the equipment, or the EFU is used as the air supply for the whole room, unclear protection boundaries, air flow interference, or acceptance disputes may arise. Let’s start with several practical aspects.

First clarify the protection boundary: room level or equipment level

The protection object of room FFU is a room or area, and the evaluation scope is usually determined based on the entire room boundary, particle size, and occupancy status. The protection objects of the equipment-side EFU are the inside of the equipment, the cavity or local workstations. The evaluation scope is smaller, but it is more affected by mechanism blocking, door opening actions and exhaust switching.

If the protection object is an open workstation or a key operating point, you can refer to What are the prerequisites for purifying only key workstations? , first confirm whether the boundaries of sensitive links and the forward and backward transfer are controllable. If it is a closed equipment cavity, it needs to be planned separately according to the air flow path inside the cavity. For specific methods, please refer to How to plan clean air supply for closed equipment cavities?。

Unclear boundaries can lead to misaligned equipment selection. For example, the room requires ISO 7, but a certain wafer exposure point inside the equipment requires higher protection. In this case, you cannot rely solely on the room FFU, nor can you directly apply the room level to the inside of the equipment.

The relationship between the air intake source and the exhaust air is different

Room FFU usually takes air from above the ceiling, filters it and sends it into the room, and then circulates it through the return air or exhaust path. Its intake air source, return air resistance and room pressure differential are part of the system design.

The air intake source of the equipment-side EFU is more complex. It may take air from the room where the equipment is located, or it may take air from the internal circulation of the equipment, or it may be connected to an independent air duct. Depending on the source of air intake, the EFU's filter life, contamination risk and system resistance will vary.

If the EFU takes air from the room, and the room itself has particle fluctuations, the inlet load of the EFU will increase; if the EFU takes air from inside the equipment, the internal dust may directly enter the EFU inlet. Therefore, the air inlet location and pollution path of the EFU must be clearly defined, and the air inside the equipment cannot be assumed to be suitable for circulation.

The exhaust relationship is also critical. There needs to be a balance between equipment exhaust, process exhaust and EFU air supply. If the exhaust air volume is greater than the supplemental air volume, the cavity may form a negative pressure and suck background air through the gaps; if the EFU air supply volume is too large, it may interfere with the exhaust air collection effect. For specific pressure differences and airflow paths, please refer to How to plan clean air supply for closed equipment cavities?。

Avoid two sets of airflows interfering with each other

When room FFU and EFU are running at the same time, the two sets of air flows may interact with each other at equipment openings, door gaps or maintenance channels. Frequently asked questions include:

• The EFU entrance is affected by room air supply, resulting in changes in inlet air volume or direction;

• The exhaust air of the equipment draws away the EFU protective airflow, causing insufficient wind speed in key areas;

• The lateral airflow of the room FFU interferes with the local protective boundary of the EFU;

• When the equipment is shut down or the door is opened, background air enters the inside of the equipment through the openings.

The operational status of the room and equipment should be checked at the same time during verification. If you only measure the wind speed on the EFU outlet surface, it cannot tell whether the internal protection of the equipment is effective; if you only measure the particles in the room, it cannot tell whether the key locations inside the equipment meet the standards.

The sampling points should be arranged to cover sensitive locations inside the equipment, 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?。

Control linkage: separate settings or unified management

Room FFU and EFU usually require different control logic. The room FFU may operate in different zones according to duty, work, and energy-saving modes; the EFU may need to be linked to equipment start and stop, door opening, and exhaust switching.

If the two systems need to be managed uniformly, they can be combined The FFU group control system configures operation strategies according to regions and time periods. However, the linkage logic must be clear: who starts and stops first, whether the EFU slows down or alarms when the door is opened, how the EFU responds when the exhaust air is switched, and how to recover after maintenance.

Control addresses and partition rules should be unified in the early stage to avoid different batches of equipment being unable to access the same system later. This is especially important when modular expansion, please refer to What are the expansion conditions for using independent modules in clean systems?。

Equipment selection: FFU and EFU parameters cannot be mixed.

When selecting room FFU, check the working point with filter, external static pressure, installation dimensions, sealing method and maintenance direction. For specific judgment, please refer to Why should we look at the complete performance curve when selecting FFU? and Is FFU's nominal air volume tested with a filter?。

The equipment-side EFU selection also requires additional consideration of the internal space of the equipment, mechanism shielding, air inlet interface and exhaust relationship. Can be referenced EFU equipment end fan filter unit , check the applicable conditions of different structures.

Filter selection should correspond to target particle size and actual resistance.The HEPA and ULPA filter pages have parameters for different levels of products. When selecting, check the efficiency of the specific model at the target air volume. 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?。

The installation location should be away from obstructions and should be convenient for filter element replacement and maintenance. Insufficient maintenance channels will increase subsequent expenditures. This is reflected in what later expenses will be increased due to insufficient maintenance channels . There is a more specific cost analysis in

Project judgment example

In a semiconductor equipment project, the room uses FFU to maintain background cleanliness, and the wafer transmission path inside the equipment uses EFU to protect it. During debugging, it was found that after the equipment exhaust was started, the wind speed in the EFU protection area dropped. The investigation found that the exhaust air volume was greater than the supplementary air volume, and the negative pressure in the cavity sucked background air through the door crack. Adjustment method: Rebalance the exhaust air and supplementary air, and increase the door opening linkage instead of replacing the EFU filter with a higher efficiency.

Another project installed the FFU above the open workstation, while the EFU was installed on the side of the equipment. During operation, it was found that the lateral airflow of the FFU interfered with the local protective boundary of the EFU. Adjustment method: adjust the FFU air outlet direction, add baffles, and re-measure the wind speed at key positions of the workstation. After adjustment, the two sets of airflows resume synergy.

These two situations illustrate that the division of labor between EFU and FFU not only involves different equipment locations, but also involves the air inlet source, exhaust relationship, control linkage and verification scope. This must be confirmed together during the design phase.

Key points for selection and acceptance inspection

Aili industrial equipment supporting support

Aili Industry covers motor manufacturing, independent research and development and production of fans, control system development, sheet metal processing, air filter manufacturing and complete machine assembly. For EFU and FFU collaborative projects, equipment-side EFU, room FFU, HEPA/ULPA filters, group control systems, air volume, static pressure, and installation interfaces can be uniformly checked to connect equipment configuration with on-site evaluation boundaries and reduce the disconnect between component parameters and the working conditions of the entire machine.

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