"GEEX – ACEX – CAEX – SOEX – precisely monitor demanding exhaust air volumes in semiconductor cleanrooms"

Fig. 1: Different air qualities are separately maintained in semiconductor cleanrooms. (Photo: Luftmeister GmbH)

Fig. 2: Luftmeister "Freiburg 1-inch", the special flow measurement sensor coated with Halar. (Photo: Luftmeister GmbH)

Fig. 3: Overview of the calibration points in a specific project (4 air types with 5 measuring devices). (Source: Luftmeister GmbH)

Fig. 4: Air volume flow calibration stand of Luftmeister GmbH. Here, with the highest precision, between 25 and 36,000 m³/h, various Luftmeister measurement solutions are calibrated. (Photo: Luftmeister GmbH)

Indoor environments are often characterized by a high-purity supply air facing a heavily contaminated exhaust air. For example, in semiconductor production with its wet chemical manufacturing steps, aggressive exhaust air qualities are generated.

To prevent chemical reactions between different types of exhaust air, but also to distinguish cleanly between explosion-proof zones (Ex zones) and non-Ex zones, it has proven effective here to separate the following types of exhaust air (see also Fig. 1):

– GEEX – General exhaust – this is the (largely) unpolluted, "normal" exhaust air without Ex requirements, which also does not demand special precautions regarding the chemical resistance of the materials used.
– ACEX – Acid exhaust – this acid-containing exhaust air is highly corrosive. For this reason, the corresponding pipelines are usually coated internally, for example with E-CTFE, the so-called "Halar".
– CAEX – Caustic exhaust – caustic exhaust air, usually based on alkaline substances, which in aqueous solution is corrosive and can destroy living tissue. These pipelines are also often coated depending on the concentration.
– SOEX – Solvent exhaust – solvent-containing exhaust air, which is generally less aggressive but must be operated in Ex zones to prevent explosions caused by sparking.

Operators of such exhaust systems are faced not only with the task of sensibly separating these air types from each other. Furthermore, it must be ensured that neither too much nor too little exhaust air is extracted. "Too much" exhaust air corresponds to unnecessary waste, as it results in higher fan power consumption, more frequent filter changes, and other avoidable costs.

On the other hand, "too little" exhaust air can have even more serious consequences:

– Semiconductor production equipment (e.g., wafers) is very expensive. To maintain flawless operation within the defined range, a minimum exhaust volume must be extracted to prevent contamination or corrosion. In this regard, the (verifiable) extraction of a certain minimum exhaust volume is often a fundamental requirement for maintaining process safety and warranty commitments.
– Occupational safety also applies: if too little exhaust air is extracted, personnel may be endangered. This is especially true if individual processes are not hermetically sealed and backflow into the work area can occur.

But how can these pipelines be professionally monitored regarding their exhaust flow? Luftmeister GmbH from Kirchzarten near Freiburg, a specialist in air flow and air heat flow, has developed very specific measurement solutions for this purpose.

A measurement solution tailored precisely to the application (see Fig. 2) has been created,
– whose process adaptation (probe installation) is constructed precisely to fit the type of connection present at the customer's site in the pipelines, e.g., via a 1" connection or a special clamp flange connection. This eliminates the need for modifications to install the measurement solution.
– whose media-contacting parts for ACEX and CAEX are fully coated with E-CTFE (Halar), ensuring high durability even in demanding exhaust air conditions.
– which distinguishes, depending on the air type, between Ex- and non-Ex transmitters (see table in Fig. 3). The highly precise transmitter Luftmeister VS 48 is used.
– which has been calibrated and adjusted at 11 calibration points in the Luftmeister GmbH's air volume flow laboratory (see table values in Fig. 3 and calibration device in Fig. 4).

The calibration process ensures that the measuring device already has its accuracy confirmed upon delivery, so it no longer needs to be calibrated on-site. This provides higher accuracy and eliminates the need for handheld measurement devices in contaminated air, which would be required for local calibration.